Stopping not on demand, or Why did the wine stop fermenting, did not ferment, or does it ferment poorly? Changing the composition of the wort during fermentation

Page 4 of 6

It is noted that some wines with residual sugar easily and spontaneously become a medium in which secondary fermentation develops. In other cases, on the contrary, the completion of the transformation of sugar is slow and difficult even after massive inoculation with yeast, aeration and the addition of ammonium salts.
In this connection it is appropriate to report a laboratory experiment which shows well the importance of anaerobiosis in relation to the difficulties of re-fermentation. High-sugar grape must (285 g/l) was fermented in air (in vials closed with cotton swabs) and without air (in vials closed with pointed tubes) at three different temperatures. In table. 3.12 shows the course of fermentation, which in all cases stops prematurely, leaving more or less unfermented sugar.
But the purpose of this experiment was to investigate the fermentability of the medium obtained after the first fermentation in order to clarify the role of anaerobiosis and temperature in these different stops of fermentation. The wines obtained in different bottles were diluted with water and brought to the same concentration (8° Baumé and 8% alcohol by volume). Thus, these different environments were made comparable. Ammonium phosphate was added to the media, filtered and sterilized at 80°C, then inoculated with a yeast distribution prepared from the same race as in the first experiment, closed with a pointed tube, and placed in a thermostat at 23°C. After that, the rate of sugar fermentation and yeast growth was compared in these different media, as well as in a medium prepared from the same wort, having the same sugar content and alcohol content, but not subjected to fermentation (control).

Table 3.12
Results of must fermentation depending on anaerobiosis conditions and temperature

batch number	Aeration conditions	Temperature, °C	Days when fermentation stopped	Number of yeast cells at the time of fermentation stop (1000 cells per 1 mm3)	Fermented sugar at the time of fermentation stop, g/l
	On air


	Without air access

					205

In table. 3.13 shows the results of after-fermentation. From this table it can be seen that the media under consideration can be divided into two categories: a) those that ferment at a rate of the same order as the control (I, II, III, VI), i.e. for which the first fermentation was carried out in air or without access to air, but at elevated temperature; b) those that ferment much more slowly than the control (IV, V), i.e. those that have undergone the first fermentation without air and at a low temperature. In the first case, the main factor limiting fermentation and causing it to stop was temperature, in the second case, anaerobiosis.

Table 3.13
Results of post-fermentation of media already subjected to the first fermentation

option number	Number of yeast cells (1000 cells per 1 mm3)	Fermented sugar, g/l
option number






Control

In conclusion, it can be said that the growth of yeast in a medium with residual sugar and the development of a new fermentation proceed much more slowly when the first fermentation occurs under conditions of complete anaerobiosis; at the same time they do not depend on the temperature (from 17 to 25°C) realized during the first fermentation. A high temperature under anaerobic or aerobic conditions, which quickly and abruptly stops fermentation with a large amount of residual sugar, creates a normally fermentable environment.
From the point of view of theory, the difference in the behavior of yeast during the after-fermentation of the medium, which was subjected to the first fermentation under different conditions, is a sign of a change in the medium due to the disappearance of growth substances or the formation of antibiotics. This hypothesis, formulated many years ago, requires experimental confirmation.

Sugar content and fermentation cessation

A study was made of the effect of sugar and alcohol content on the fermentation process of three types of media prepared from the same wort as in previous experiments. Fermentation was carried out at the same temperature (25°C) under conditions of complete anaerobiosis. Comparative results are given in table. 3.14.
Effect of sugar and alcohol content on must fermentation
Table 3.14

The initial alcohol ness, % about.	Initial sugar, g/l	Final number of yeast (1000 cells per 1 im3)	Fermented sugar, g/l	Final alcohol content, % vol.
The initial alcohol ness, % about.	Initial sugar, g/l			Final alcohol content, % vol.
	226 (cont. role)

In all three environments, fermentation ceased approximately on the 16th day. From Table. 3.14 shows the profound effect of alcohol and sugar on yeast reproduction from the very beginning, so that in the medium where sugar was added, the amount of sugar that the yeast can ferment is less than that fermented in the control medium. Here, sugar acts as a limiting factor, no less important than alcohol.
In addition, in the experiment on the secondary fermentation or in the comparative experiment on fermentation, carried out, like the previous experiment, in musts with the addition of sugar and alcohol, the secondary fermentation proceeded more difficult than in the control sample. Approximately the same effect of sugar and alcohol was observed in other experiments.
To this it should be added that other reasons can contribute to stopping fermentation. In some cases, fermentation stops were noted at a very high concentration of coloring substances. According to the authors' observations, the addition of activated charcoal (from 10 to 20 g/hl) often also activates the post-fermentation of white wines with stopped fermentation.

A stalled or stuck fermentation is a real problem in winemaking that even the most experienced winemakers face. There is almost always a solution. So, in this article, we will figure out why homemade wine has stopped fermenting, why it can ferment poorly, and also what to do about it.

If an experienced winemaker who has been making wines constantly and for many years tells you that he has never had problems with fermentation, then most likely he is lying to you or not telling you something. There are a number of basic rules that need to be taken into account when setting up any wine for fermentation. By following them, the likelihood of problems with fermentation is reduced to a minimum, but there are always force majeure circumstances. And if an experienced winemaker is well acquainted with the basic rules and always observes them, then he is powerless against force majeure.

To better understand the fermentation process and you and I did not have a misunderstanding, first read the articles with recipes and wines, where all winemaking processes are described in great detail.

Experienced winemakers are not frequent guests on our site. For decades, smart books, specialized sites and communities have existed for them. We do not grab stars from the sky - we are amateurs and we write exclusively for amateurs. Therefore, this article will begin with an analysis of the basic rules for good fermentation, possible problems and ways to solve them. More extravagant causes of "stuck" fermentation, which happen extremely rarely and are mainly associated with wine diseases, we will consider sometime in another article.

Go through this list and read each item carefully. Here are the most common causes of "stuck" fermentation. Some problems and ways to solve them will be described not only for wild yeasts, which beginner winemakers often work with, but also for pure yeast cultures (hereinafter referred to as CKD).

Fermentation hasn't started yet

Do not expect active fermentation, with foam and dancing, to begin 10 minutes after extraction of juice or addition of CKD. This usually takes from 3 hours if some strains of CKD are used (in most cases with cultural yeasts, the wine starts to ferment immediately) or up to 2-3 days if it is wild yeast. Yeast, once in a favorable environment for life, the first thing they begin to multiply and only after that they break into the absorption of sugar. This can take a long time if something interferes with it. Therefore, the start of fermentation is highly dependent on the ambient temperature, the raw materials used, the sugar and acid content.

What to do?

Wait 3-4 hours if CKD was added, or up to 3-4 days if fermented with wild yeast. If fermentation does not start, then something is wrong with the yeast or wort, which means you first need to analyze the juice (find out its sugar content and acidity) and add fresh yeast or yeast starter from raisins, raspberries, etc. Read the article further.

Too little oxygen during primary fermentation

As mentioned earlier, the first couple of days, the yeast spends all its energy on reproduction, and only after their number has reached a certain mass, they begin to think about food. At this stage, yeast cells use oxygen for their replication. If during the period of wine fermentation or immediately after adding CKD to the must, a water seal is installed on the fermentation tank, the yeast will receive less oxygen and their reproduction will be greatly delayed. Such wine ferments sluggishly and there is a high risk of contamination of the must.

What to do?

In the early days, do not install a water seal on the fermentation tank. It is better to close the neck of the container with gauze or cloth. It will also be useful to “ventilate” the wine before putting it into fermentation under a water seal. To do this, the wort cleared of pulp can be poured several times from one vessel to another, preferably from a great height, so that it is saturated with oxygen.

Temperature difference between wort and sourdough

Before adding CKD to the wort, they must be prepared (popularly “fermented”). To do this, mix a glass of water or wort, a tablespoon of sugar, sometimes orange juice for feeding. Yeast is added to this artificial medium and wait 15-40 minutes for it to activate. After that, the starter is poured into the main wort. But if the starter temperature deviates from the temperature of the wort by at least 5-7 o C, the yeast experiences a temperature shock and, as a rule, dies. The difference in temperature can also cause a long start of fermentation.

What to do?

Check that the temperature of the wort and yeast starter is the same. To do this, it is enough to keep them in the same place for 15-30 minutes.

Yeast added early after sulfites

It is advisable to treat all wines with sulfites (sodium bisulfite, Campden tablets, or, more simply, sulfur, SO2) before adding CKD. Sulfites sterilize the wort, destroying all third-party microorganisms. Sulfur begins to dissipate in the air as a gas and gradually leaves the juice. This takes about 18-24 hours. After that, you can safely add CKD and start making wine from scratch.

What to do?

After using sulfur to sterilize the juice, wait the prescribed 24 hours and only then add the yeast. At this time, the container with wine does not need to be closed, because the sulfur should come out of the juice completely. It is better to do with gauze or a clean cloth.

Yeast needs nutrients

In addition to sugar, yeast, for its vital activity and replication, needs nitrogenous food, amino acids and vitamins. In grape juice, as a rule, all these substances are present in sufficient quantities. But the same cannot be said about fruit and berry juice. Always add liquor store yeast feed first if possible. You can also get by with some drugs from the pharmacy.

What to do?

In the primary fermentation, add yeast feed from the liquor store to the wort containing nitrogen (diammonium phosphate), vitamins, minerals, fatty acids, and more. Carefully follow the instructions on the package. In the late stages of fermentation, when the wine has suddenly stopped fermenting, it is better not to add such complexes, as they can become beneficial food for unwanted bacteria. It is better to get by with a pure source of diammonium phosphate (usually 1g/l). You can also add thiamine hydrochloride (25 ml per 3.5-4 liters of wine, mix well) - you can find it in pharmacies.

The wine stopped fermenting in the late stages (after a week)

The water seal is not sealed

Without a water seal, as they say, you can’t brew wine. It is necessary for the unimpeded removal of carbon dioxide from the fermentation tank and not for oxygen to enter it. The carbon dioxide released during fermentation must be removed, since its high concentration negatively affects the vital activity of the yeast, and can also create serious pressure inside the closed container. The constant supply of oxygen can cause the development of pathogenic microorganisms that will turn your drink into vinegar or, worse, cause the wine to become sick.

A good factory water seal is a guarantee of stable fermentation.

A hermetic water seal is an indicator and guarantor of proper fermentation. The air bubbles released by him indicate that fermentation is proceeding normally. The same thing happens with a rubber glove (an undesirable alternative to a water seal) - if it is inflated, then everything is in order. If the tightness is broken, then the glove will not inflate, and the airlock will not blow bubbles, and you will decide that something is wrong with the fermentation process. In addition, a leaky water seal late in fermentation will allow oxygen to enter, which will cause more serious problems.

What to do?

Check the water seal for leaks. If necessary, cover the joints with silicone, plasticine or any other sealant. Remove the water seal only if necessary. Do not install an airlock during the first few days of fermentation (read previous points).

The temperature regime is not observed

Yeast needs a constant temperature within a certain range to survive. If the ambient temperature drops below 10 ° C, the yeast goes into suspended animation and fermentation slows down or stops altogether. If the temperature exceeds 30°C, the wild yeast will die (some types of CKD can handle higher temperatures). The optimum temperature for the fermentation of any wine, grape or fruit, is 18-24 o C.

Temperature fluctuations are a very common problem. If the temperature of the wort changes by 5-7°C in a short period of time, most of the yeast will die. Even larger drops can destroy the entire colony. Especially dangerous are temperature drops in the late stages of fermentation, when the concentration of alcohol already causes inconvenience to yeast cells.

What to do?

Provide wine with a constant temperature in the range of 18-24 ° C. If the fermentation process has slowed down a lot, then it is advisable to maintain the temperature in the region of 21 ° C. If the temperature has exceeded 30 ° C and the yeast has died, restart the fermentation.

Too much sugar

This is the scourge of the novice winemaker and is one of the most common problems today. Yes, yeast converts sugar into alcohol. Yes, sugar is their main food source. But as soon as its concentration exceeds a certain maximum, the yeast reduces its activity. Sugar in this case plays the role of a preservative. When the sugar content of the wort reaches 20% (according to the hydrometer 1080-1090 g / dm 3), fermentation practically stops. For the same reason, wine often stops fermenting after adding sugar. The optimal sugar content for normal wine fermentation is 10-15%.

Buy a hydrometer and always measure the sugar content of the must - this will save you the most common mistake novice winemakers make.

What to do?

If the sugar content of the wort exceeds 20%, it is necessary to dilute it with clean water (you can start with 15% of the total wort volume). The same should be done with too dense wort. If necessary, restart the fermentation. If you are preparing dessert or liqueur wine, always add sugar in portions, on the 2nd, 4th, 7th, 10th day of fermentation in equal parts, dissolving it in a small amount of fermenting wine.

The acidity of the wort is too high or too low

Grape juice, as a rule, contains the optimal amount of acids and nutrients necessary for the normal functioning of yeast cultures. The same cannot be said about other fruits and berries, the juice of which should be prepared before fermentation. The most difficult thing for a novice winemaker is to cope with the acidity of the must. It is believed that the optimal acidity of grape must should range from 3.5 to 5.5 pH, ideally around 4 pH. If the acidity of the must is below 3.5 pH, fermentation is severely inhibited or may stop altogether. If this value is above 4 pH, there is a risk of wine disease due to other microorganisms.

What to do?

Get a pH meter. If the acidity is below the required level (pH>4), add the juice of 1-2 lemons per 3-4 liters of wine or use tartaric acid from the store. Apple wines are best acidified with malic acid. Pear cider, the recipe of which is described in the article, cannot be acidified with citric acid. Otherwise, when the acidity is above the prescribed level (pH<3,5), вино нужно разбавлять чистой водой, пока его кислотность не достигнет нужного уровня.

Too much alcohol

It should be understood that alcohol is also a preservative. With an increase in its concentration in the wort, the activity of the yeast decreases markedly. When the must strength reaches 12-14%, wild yeast falls into suspended animation or dies, settling to the bottom of the container in the form of a dense sediment. Determining the alcohol content of wine after rapid fermentation is quite problematic if you do not have a hydrometer and you did not measure sugar at the beginning. However, 12-14% alcohol in the drink is felt when tasting. Before adding sugar, always calculate how much alcohol will come out of it. At least according to the average: 1 g of sugar \u003d 0.5-0.6 ml of absolute alcohol.

What to do?

Proceed to the next step: clarify the wine, age and bottle. If you want to continue experimenting and increase the strength of the wine, add alcohol-resistant CCDs.

Fermentation is over

If homemade wine isn't fermenting, it might just be ready. On average fermentation with wild yeast takes between 20 and 30 days to ferment vigorously, with CFD fermentation can be much faster depending on the strain of yeast. However, elevated ambient temperatures during fermentation, as well as sufficient nutrients for the yeast, can greatly speed up the process. Under ideal conditions, fermentation can be completed within 2 weeks, and CKD can process all the sugar in 5-7 days.

What to do?

Proceed to the next step: drain the wine from the sediment, put it on a quiet fermentation in a cool room, and then bottle it. But before that, you need to make sure that the fermentation is really over. Taste your wine and if it is bittersweet, sugar is not felt in it, then this is a sure sign of the end of fermentation. A hydrometer will also help. If the specific gravity of the wine is 998-1010 g/dm 3 , the wine is ready for clarification and bottling.

Pathogenic microorganisms have developed in the wort

Diseases of wine is a complex topic that requires a separate capacious material. The wort may become moldy, acetic or other undesirable fermentation may be activated in it. In such cases, it is difficult to do anything and the wine is often simply poured out. Always use sterile equipment and wash your hands before handling wine material. If signs of the disease were detected at the first stage, the wort can be sterilized by heating or, after which ChKD or yeast starter can be added.

A typical picture of homemade wine disease.

Restart fermentation

If all the recommendations described above did not help, then the yeast died or was initially dead, and a priori fermentation could not start. In such cases, only restarting the fermentation with yeast sourdough or CKD will help. And since something went wrong with wild yeast initially, it’s better to go to a liquor store and get cultured yeast. That will be more reliable.

In most cases, when the wine suddenly stopped fermenting, and there were no prerequisites for this, it is enough to introduce the so-called killer yeast, which quickly replicate, displace other strains, but at the same time make good wine. These yeasts definitely include Red Star Premier Cuvee, Red Star Champagne and Lalvin EC-1118. Also, Lalvin K1-V1116 yeast (Montpellier) proved to be excellent for restarting fermentation.

Before pitching the yeast, the wort still needs to be corrected if one of the problems described above has been noticed. For example, if the wort is too sweet - dilute with water, not sour enough - add acid.

Before adding yeast to restart fermentation, it must be prepared. To make everything go like clockwork, it’s better to work according to this algorithm:

Prepare CKD yeast starter (strain recommendations above)

sterilize a half liter jar
add 250 ml of pure water to it at a temperature of 27 ° C
add 1 teaspoon of sugar
5-10 ml lemon or orange juice
a pinch of yeast nutrients*
1 heaping teaspoon of yeast
seal the neck of the jar with a cotton plug
leave the jar in a warm place

* instead of nutrients, you can add 0.5 teaspoon of thiamine hydrochloride, which acts as an antidepressant for yeast.

Wait 6 hours for the yeast to get stronger and ready to be added to the wort.
Pour the yeast into a large container and add 250 of wine that has stopped fermenting to it.
Wait another 6 hours and add 500 ml of wine.
Every 6 hours, double the amount of wine added until all the must is in the container.

This method of restarting fermentation in almost 100% of cases shows a good result, because the yeast gradually gets used to the must and easily adapts to it. If fermentation did not start after 3-6 hours, then one of the problems described above takes place. Read the article again!

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Fermentation of grape must , the biochemical process of converting grape must into an alcoholic product under the action of an enzyme complex of wine yeast, leading to the breakdown of carbohydrates into ethyl alcohol, carbon dioxide and the formation of secondary and by-products. The process of grape must fermentation has been known and used since ancient times. L. Pasteur was the first to create a biological theory of fermentation and established the role of yeast in alcohol fermentation. Scientists made a great contribution to the disclosure of biochemical features and the development of optimal modes of fermentation of grape must: the French J. Ribero-Gayon, P. Ribero-Gayon, E. Peino, the Italian M.A. Joslin, Russian V. I. Nilov, M. A. Gerasimov, G. G. Valuiko, and others. Fermentation of grape must can be carried out in various ways at different temperatures. Existing methods for fermentation of grape must are divided into periodic and continuous. Periodic fermentation of grape must is carried out in barrels, vats, bottles, reinforced concrete, metal and other tanks (see), at atmospheric or excess pressure (see). The wort for batch fermentation can be fed simultaneously or in stages. In the latter case, the fermentation of grape must is carried out by topping up in all types of tanks. Continuous fermentation of grape must is carried out on a special. installations consisting of one or more tanks interconnected by pipelines. Temperature Fermentation of grape must is selected depending on the type of end product and the characteristics of the technological process in different countries. In the CIS countries, the optimum fermentation temperature for high-quality white table and champagne wine materials is 14°-18°C. Ordinary dry wine materials are prepared Fermentation of grape must at a temperature of 24°-26°C. Fermentation of grape must in barrels. After clarification, the must is pumped into barrels for fermentation. Simultaneously with the wort, a distribution of pure yeast cultures arrives. Barrels are filled with 65-75% wort in order to prevent the wort from overflowing through the tongue. The upper tongue-and-groove hole of the barrel is closed with a hydraulic fermentation tongue. Fermentation of grape must in barrels with a capacity of 35-50 dal, as a rule, proceeds at a temperature of 15°-24°C, i.e. at an optimal level for dry white wine materials, due to the natural heat exchange of the must with the environment. The fermentation of grape must proceeds normally at a temperature in the fermentation shops of 14°-16°C. Wine materials prepared by fermentation of grape must in barrels have high organoleptic qualities. However, this method of fermentation is laborious, requires large capital costs, and therefore has a limited distribution.

Fermentation in large tanks.

In a tank with a capacity of 1-2 thousand decalitres or more, a distribution of pure yeast cultures is fed in an amount of 2.5-3% of its volume. Then comes the clarified wort in the amount of 75% of the capacity of the tank. The fermentation temperature is regulated with the help of various types of remote tubular coolers, coolers located in fermentation tanks, irrigation of the tanks with water, as well as with the help of water or other refrigerants circulating through the cooling jackets of the tanks. Fermentation is carried out at a temperature of 14°-26°C for 5-6 days, depending on the type of wine materials. The automatic temperature control system for fermentation in tanks with a capacity of 15-50 thousand dal consists of coolers, centrifugal pumps and thermostats. When producing table wine materials, fermentation is carried out at a temperature of 12°-16°C for 20 or more days. It is possible to ferment the wort at temperatures up to 26°C, however, the tanks must be equipped with defoamers. Fermentation in large tanks with a capacity of 15-50 thousand decalitres with automatic temperature control is used in Moldova and Azerbaijan at primary winemaking plants with a processing capacity of 40 thousand tons of grapes per season. Abroad, fermentation in large tanks with a capacity of 10-25 thousand deciliters is widely practiced at wineries in the USA, France, and Spain.

Top-up (fractional, stepped) fermentation methods.

The topping-up fermentation of grape must is used for the preparation of dry wine materials in metal and reinforced concrete tanks with a capacity of 1-2 thousand deciliters. First, a distribution of pure yeast culture is introduced into reinforced concrete tanks, and the tank is filled by 30% with clarified wort. After 2 days, when the stage of rapid fermentation begins and the temperature of the fermenting wort rises to ~26°C, another 30% of the clarified wort is added with a temperature of 16°-20°C. After topping up the second portion, the temperature of the fermenting wort is reduced to 22°-24°C. When the temperature of the fermenting wort rises to ~26°C (after 2-3 days), another 20% of the wort is added. In metal enameled tanks Fermentation of grape must by topping up is carried out as follows. First, the tank is filled to 50% with clarified wort, and a pure yeast culture is added. After 2 days, clarified wort is supplied in the amount of 25% of the tank capacity, after 4 days - another 12-13%, and the fourth portion of the tank is topped up almost to the top. In large metal tanks with a capacity of 15-50 thousand dal Fermentation of grape must by topping up becomes more difficult due to a decrease in specific surface area to 0.7-1.0 m 2 /m 3 . The number of added portions of clarified wort increases to 5-12. The volume of portions of the added wort and their temperature depend on many factors, therefore, under specific conditions, nomograms are proposed to determine them (Fig. 1 and 2).

The process of fermentation of grape must is carried out as follows. Clarified wort is initially supplied to the tank at a temperature of 10°-12°C in the amount of 15-20% of the total volume of the tank and the distribution of pure yeast culture in the amount of 2-4% of the wort volume. After fermentation of the fermentation mixture to a residual sugar content of 1-2 g/100 cm 3, clarified wort is supplied for fermentation daily in the amount of 12-28% of the fermenting wort volume, depending on the average daily temperature and sugar content of the wort. Fermentation continues for 6-12 days at a temperature of 24°-26°C. For thermally insulated large tanks Fermentation of grape must by the topping method is proposed to be carried out continuously at a dilution rate when the process is carried out at a close to stationary phase of yeast growth under conditions of a high concentration of ethyl alcohol in the medium. Fermentation of grape must in a continuous flow has a number of advantages over batch fermentation. With continuous fermentation, the fermentation period is eliminated due to the fact that fresh wort is fed in small volumes into a rapidly fermenting wort with a high concentration of yeast cells. The period of fermentation of residual sugar is also excluded, because. continuous fermentation plants produce wine material containing 2-3 g/100 cm 3 of sugar. The exclusion of periods of fermentation and after-fermentation leads to an increase in the productivity of a continuous installation compared to the fermentation of grape must in a periodic way in tanks of the same capacity. Fermentation of grape must in a continuous flow allows you to fully mechanize and automate the process. In a continuous stream, the wort is fermented at an alcohol content of St. 4% vol., which allows the process to be carried out only on wine yeast of the Saccharomyces vini species and, accordingly, to obtain higher quality wine materials (see). Fermentation of grape must in a continuous way allows you to regulate the chemical composition of wine materials in terms of nitrogenous substances, ethyl alcohol, sugar, higher alcohols, aldehydes, glycerin, to a wider range, to obtain high quality wines. Installations for continuous fermentation of wort in a stream have been developed: BA-1 (for the preparation of white table dry wine materials), VBU-4N (for the preparation of white dry, semi-dry, semi-sweet, strong and dessert wine materials), "Ukrainian", "Moldavian", etc. .

Microbiological conversion of sugars (glucose and fructose) into ethyl alcohol by wine yeast. This is the main process in winemaking. All others are auxiliary. As fermentation goes on, we will get such wine.

In the production of dry wines - sugar must ferment completely.
In the production of semi-sweet and semi-dry - partially.

The situation becomes a little more complicated in the production of fortified (with the addition of alcohol) and dessert (special technology) wines. It is impossible to achieve high alcohol (14-17%) here by natural fermentation. At 17% alcohol, the wort self-preserves and the yeast dies. Moreover, 14-17% sugar should be present in the wine. Therefore, fermentation is carried out until the necessary sugar remains in the must, and then alcohol is added, bringing its content in the wine material to the required level. That is, fermentation is interrupted by alcoholization. According to the correct technology of fortified wines, natural alcohol should be at least 3% out of 14%.

There is another type of fermentation that occurs in winemaking. it bacterialmalolactic fermentation . It is produced by lactic acid bacteria, the same bacteria that cause milk to go sour. They decompose malic acid into lactic and carbon dioxide, at the same time "grabbing" other organic compounds. If such a process occurs spontaneously and is not planned by the winemaker, then it can lead to damage to the wine material. There are preparations from cultural strains of lactic acid bacteria. They are used to improve the taste of highly acidic wines. But to start such a biological acid reduction, first it is necessary to carry out a partial deoxidation of the wort with chalk, then add this drug, raise t to +20 C and stop the process by sulfitation in time. At home, this is all poorly acceptable and irrelevant.

For the processing of highly acidic wort, a special acid-reducing yeast called acidodevoratus, which in Latin means "acid scavengers", is better suited. During normal alcoholic fermentation, they convert malic acid into alcohol and carbon dioxide by-products. Therefore, this type of fermentation is called apple-ethanol . It is used to make dry wines from raw materials with excessive acidity.

Some important information about alcoholic fermentation.

At temperatures below +10 C, fermentation stops.

At temperatures from +10 C to +27 C, the fermentation rate increases in direct proportion, that is, the warmer - the faster.

From 1 gram of sugar during fermentation is formed:
- ethyl alcohol 0.6 ml. or 0.51 gr
- carbon dioxide 247 cubic cm or 0.49 gr.
- heat dissipated into the atmosphere 0.14 kcal

Sugars are actively assimilated by yeast, with the sugar content in the wort ranging from 3% to 20%.

As soon as the concentration of alcohol in the must reaches 18%, then all wine yeasts die. There are some types of cultural yeast that die already at an alcohol content of 14%. These are used to make wines with residual sugar.

The carbon dioxide released by the yeast cells in the wort slows them down. A bubble of gas, while it is small, "sticks" to the wall of the yeast cell and prevents the flow of nutrients to it. This situation continues until the cell "inflates" this same bubble to a certain size. Then the bubble floats up and drags the yeast cell with it up to the surface of the fermenting liquid. There it bursts, and the cell sinks to the bottom of the fermentation tank. This process is conventionally called "boiling", and is considered a waste of time in the process.

Types of yeast.

Fermentation can be carried out on wild yeast that live naturally on the grape bush, or on cultural yeast bred and selected by man in the laboratory.

The choice of yeast depends on the will of the winemaker.

Wild yeast and spontaneous fermentation- live on berries of grapes and a grape bush. When processing grapes for wine, other microflora also enters the must. In freshly squeezed grape juice, on average, mold fungi are contained in a share of 75 to 90%, and various types of wine yeast 10-20%. Some of the microorganisms already at the first stage die in the wort due to the high acidity of the juice and sugar content. Some try to compete with wine yeast and begin to multiply, but they soon die as well, so the supply of dissolved oxygen in the must ends. Wine yeast by this time reaches a high concentration (about 2 million cells per cubic cm of wort), they switch to an anaerobic, without oxygen, type of sugar processing. And, thus, they get at their disposal the entire volume of the wort as a whole.

While it is small, the greatest number is developed in the red juice of Hanseniaspora apiculata (apiculatus or spiky), in the juice of white grapes - Torulopsis bacillaris.

After the accumulation of about 4% alcohol, both species die off. From the "carcasses" of dead yeast, nitrogenous substances begin to flow into the wort. After that, active reproduction of yeast of the genus Saccharomyces, mainly of the ellipsoideus species, in Russian - ellipsoid yeast, becomes possible. They carry out both the main fermentation and the second fermentation. The last interesting thing happens, again, after the appearance of nitrogenous substances in the wort from the dead cells of fellow species.

With the accumulation of 16% alcohol, ellipsoidal yeasts die. The final fermentation is carried out by alcohol-resistant yeast oviformis (egg-shaped). But they also fall out at 18% alcohol. Now the wine material is practically sterile. Only the oxygen in the air can spoil it.

Fermentation with wild yeasts can produce high quality wines with a wide range of flavors and aromas. After all, several types of yeast that replace each other take part in their creation. But there is a significant risk of getting unfermented or low-alcohol wine if the relay race of yeast fungi is interrupted at some stage.

Cultural yeast and fermentation in pure cultures- cultural yeast is obtained as the offspring of a single yeast progenitor cell in the conditions of the microbiological industry. Therefore, the wort is populated with only one type of yeast fungus with exactly the same properties. There should not be any other microorganisms in it. In this case, it is possible to choose exactly those yeasts that will give us the product of the desired properties, for example, sherry yeast, champagne yeast, yeast for red wines, sulfite-resistant races, races with a high alcohol yield, heat-resistant, cold-resistant, acid-resistant, and so on. Competition between microflora will be excluded, and the product will most likely turn out exactly the one that the winemaker was counting on.

The wort, before the start of fermentation on pure cultures, must be freed from wild microflora. First of all, you can wash the berries in warm water with a temperature of +35 C or hold the berries over hot steam. This mode will destroy a lot of microorganisms on the skin of the berries. After draining the water, cool the raw material to +10 C, crush and get the wort in the usual way, then spend clarification . It is useless to populate the already fermented wort with cultural yeast. Wild yeast live in nature, are constantly tempered in the struggle for existence, and it will not be difficult for them to deal with cultural sissies. For the same reason, in order to give cultural yeast a head start in the struggle for the development of wort, it is better to introduce them in the form yeast wiring. They do it this way: they take about 0.5 liters of grape juice immediately after pressing. It is heated to a temperature of 80 C, poured into a sterilized glass liter jar, cooled under a sterile lid to + 25 C, and dry yeast is added. Stir with a clean spoon, cover again (without corking). Further, in the distributing tank (as our jar is now called), vigorous fermentation should occur. The optimum temperature for it is +23 C. As soon as it starts to decline, it is believed that the number of yeast cells has reached its maximum peak and it is time to place them in the wort prepared for this.

It should be noted that after numerous experiments, the modern wine industry has come to the conclusion that pure yeast cultures can be used to a limited extent, if the raw material has some drawbacks or it is not possible to maintain the correct temperature during the fermentation process.

Fermentation speed.

The best fermentation is slow fermentation. At high temperatures, the yeast so actively process the sugars of grape must that the bubbling bubbles of the resulting carbon dioxide carry aromatic, flavoring substances and even alcohol vapors into the atmosphere. The wine turns out flat, with unexpressed taste qualities, and loses its degree.

Optimum fermenting wort temperature:
- white delicate and special, champagnes - 14-18 C;
- red, pink, plain white - 18-22 C;
Also, in this range, separation of tartar from the must is better, which improves the taste of wine and the benefits of the drink.

For example, white dry ferments:
at t +10 C - 20 days,
at t +15 C - 10 days,
at t +20 C - 5 days

At temperatures from +25 to +30 there is excessive fermentation. Yeast multiply quickly and die off quickly, nitrogenous substances constantly enter the wine material, which are formed during the decomposition of dead cells, and this increases the risk of turbidity, disease, and overoxidation.

At t above +30 ° C, the yeast dies, and sugar (non-ferment) remains in the wort. In such a nutrient medium, foreign bacteria immediately begin to multiply and product spoilage occurs.

stages of fermentation.

The entire fermentation period is conditionally divided into three phases:
fermentation, violent fermentation, quiet fermentation.

fermentation- the initial period when the yeast adapts to the conditions in the fermentation tank and begins to multiply;

violent fermentation- the period when the yeast multiplied, occupied the entire volume of the wort and switched to an anaerobic way of feeding with the release of alcohol and other substances into the surrounding liquid, their number is growing;

silent fermentation- the main sugar is converted into alcohol, the number of yeast cells is reduced.

This diagram displays stationary fermentation method. It is important here that the container is filled with fermenting wort by no more than 2/3 of the volume. Otherwise, with foam in the middle phase, the contents will be thrown out. This leads to irrational use of fermentation tanks and instability of processes inside it.

Fermentation is more stable when top-up fermentation. True, this technology can only be used for the manufacture of dry wines. It is done like this:
1. First, the container is filled with 30% of the total volume with wort and yeast wiring is added to it in full; After 2 days, fermentation will go into the stage of rapid, and the wort will warm up.

2. on the third day, another 30% of prepared fresh wort is added;

3. After another 4 days, another 30% of fresh wort is poured into the tank.

The fermentation tank is thus filled almost to the top, and the fermentation process itself occurs without sharp peaks and jerks in the number of yeast and their metabolic products. And this is good for the quality of the future wine.

Fermentation "over four" - supercar.

Proposed by the French winemaker Semichon.
The main feature is that before the start of fermentation, alcohol is added to the must or pulp in the amount of 5 volume percent. This amount of alcohol is enough for all unwanted microflora in the wort to die. At the same time, the saccharomyces yeasts necessary for fermentation do not suffer at all, but continue their work in the "cleared field". But the addition of alcohol to the must is prohibited by the laws of most wine-producing countries. Winemakers go around and modify the supercart method: first, dry wine material with an alcohol content of about 10% is obtained using the supercart method, then it is added to the bulk of the must in the proportion required for this method.

Fermentation on the pulp.

It is used in the production of red wines and some fortified white highly extractive (saturated) wines. Here, during fermentation, the task is to obtain not only alcohol, but also to remove coloring, aromatic tannins and other substances from the skin and seeds.

Fermentation of pulp is always difficult. After all, it is a heterogeneous, solid and viscous mass. In addition, in order to release the necessary substances from the skin and seeds, a temperature of at least +28, and preferably +30 C is required. But at +36 C, the yeast loses activity, and at +39 C they die.
That is, a narrow temperature range remains for fermentation on the pulp.
from +28 to +32 C.

Fermentation on the pulp with a floating cap. It is carried out in vats or open containers . The wort is sulphated at the rate of 100 mg/1 kg. They fill the container with 4/5 of the volume, add the yeast layout. Stir.

After a while, violent fermentation begins. The released carbon dioxide drags all particles (flakes of pulp, skin, pieces of ridges and stalks) to the surface and keeps them afloat there. The pulp is stratified into liquid and a "cap" of the solid fraction, floating on the surface, and most often protruding above it. The upper side of the "cap" for several hours is populated by acetic bacteria, fruit flies and oxidized by air. That is, the initial stage of wine spoilage occurs - acetic acid souring. To prevent this phenomenon and improve the extraction of dyes, it is necessary to mix the contents of the container 5-8 times a day for 5 days.
As soon as the wort acquires a rich color, it is drained, the pulp is pressed and both liquids are combined and kept until the end of fermentation. This method produces the most beautifully colored and full-bodied wines.

Fermentation on the pulp with a submerged cap- in order to reduce the amount of mixing with the "floating cap" method, a simplified "dipped cap" method was invented. The "cap" is heated to a depth of about 30 cm using a grate. The number of stirrings with a submerged hat may be less, but the color of the wine will correspondingly be worse.

Both types fermentation on the pulp can also be carried out in closed containers. In this case, a layer of carbon dioxide is formed above the cap, which to some extent resists acetic acid souring and simplifies the process.

The main feature of fermentation in large tanks is an excessive increase in the temperature of the fermenting wort due to the heat released during this. A gram-molecule of sugar (180 g) releases 23.5 kcal of heat.

The relatively poor thermal conductivity of reinforced concrete, the large mass of the fermenting liquid, the close arrangement of the tanks - all this leads to weak heat radiation and heating of the fermenting must.

The negative effect of elevated temperature is as follows. Grapes and grape must contain essential oils, which later form the basis of the bouquet of wine. During fermentation, bubbles of carbon dioxide (CO 2), passing through a layer of liquid, are saturated with vapors of essential oils and carry them out into the atmosphere. From 1 liter of wort, up to 50 liters of CO 2 are released during fermentation. The higher the temperature, the greater the amount of aromatic substances is carried into the atmosphere with CO 2 . Lowering the fermentation temperature helps preserve the aromatics in the wine.

EN Datunashvili developed a method for capturing and using essential oils carried out with carbon dioxide. During the fermentation of the wort in large containers, adsorbers filled with activated carbon are installed on the communication that removes carbon dioxide in order to capture essential oils.

Essential oils eluted from coal with rectified alcohol can be used to improve the bouquet of table, strong, dessert and semi-sweet wines. For essential oils from each grape variety, it is necessary to select the appropriate wine material in order to achieve the greatest harmony. Essential oils released during fermentation are used in amounts from 0.007 to 0.03% (based on pure oils) depending on the type of wine.

With an increase in the fermentation temperature, the loss of alcohol increases, since it is also carried out with carbon dioxide.

When the temperature of the fermenting wort is up to 30°C and above, a mass death of yeast cells occurs, and at 37-40°C, fermentation stops. Sometimes even the introduction of fresh yeast wiring does not cause post-fermentation. It turns out malnutrition with a high sugar content, which in the future is a fertile ground for the development of pathogens and yeast.

Pathogenic bacteria, in particular mannitol, develop freely at elevated temperatures, enrich the wine with volatile acids and give it a peculiar foreign taste.

At elevated fermentation temperatures, dead yeast cells are more likely to undergo autolysis, as a result of which the wine material is unnecessarily enriched with nitrogenous substances.

This causes an increase in the tendency of wines to protein turbidity, to microbial diseases and the appearance of "madera" and other tones of overoxidation.

Fermentation temperature has a significant impact on the rate of fermentation of sugars, the chemical composition of the resulting wine and its quality.

With slow fermentation carried out at low temperatures, the wines are distinguished by a fresh and pure varietal aroma, harmonious delicate taste.

According to V. M. Maltabar et al., with an increase in the fermentation temperature in the range of 15-35 ° C, the content of volatile acids in wine increases from 0.25 to 1.02 g / l, the amount of aldehydes increases and the content of higher alcohols and total esters decreases . This is especially clear when determining the volatile substances of raw alcohol obtained during the distillation of wine materials fermented at different temperatures. With an increase in the fermentation temperature from 15 to 35°C, the content of ethyl acetate in raw alcohol decreases by 4 times, while acetic acid increases by 4.6 times, and isobutyric acid by 5.5 times.

In the process of fermentation, there is an intensive uptake of dissolved oxygen by the yeast and a decrease in the redox potential. According to M. A. Joslin, Eh decreases from +409 mV in the must after crushing the grapes to -10 mV at the time of rapid fermentation and to +40 mV at the end of fermentation. A. K. Rodopulo observed a decrease in Eh from 475 to 216 mV for 6 hours of fermentation.

According to Kruss, with an increase in the fermentation temperature from 7 to 20-22 ° C, an equally high alcohol content is observed in the resulting wine materials - within 16.5% vol. With a further increase in the fermentation temperature, the strength of the resulting wine materials is significantly reduced. So, if at a fermentation temperature of 25°C the alcohol content was 13.4% vol., then at 28°C - 13.1% vol., at 31°C - 11.9% vol., at 34°C - 9% vol. and at 37°C - 6.2% vol.

Prof. Krüss already in 1914 successfully fermented grape must at a temperature of 8°C. American experience shows that low temperature fermentation is more suitable for white wines. Red wines, although they are thinner in taste and have a rich bouquet, are inferior in color to wines fermented at a higher temperature.

Barret in the laboratory carried out fermentation at a temperature of 3°C for two months. He succeeded in breeding cryophilic yeast, which completes fermentation at 4°C in 45 days. In production, he carried out fermentation in vats in two stages: for a month - at a temperature of 3 ° C, then two months - at 10 ° C.

In the US, the following refrigeration fermentation scheme is now proposed: 18 days of fermentation takes place at a temperature of 4 ° C, and ends at 10 ° C. With this scheme, fermentation lasts 32 days.

Casale used for the preparation of high-quality fine wines fermentation at low temperature (3 ° C) on a special cryophilic yeast race. Fermentation at a temperature of 20°C lasted 8 days, and at 3°C - up to 30 days. The low temperature caused in the finished wines an increased alcohol content, a reduced titratable acidity and a reduced amount of volatile acids.

Kraus found that fermentation at temperatures below 6 ° C is very sluggish, and at 15 ° C - too rapidly. According to Kraus, the optimum fermentation temperature is 8-10°C.

According to Kremer's data, fermentation at 11-15°C lasted 38 days and gave an alcohol content of 12% by volume, at 6-10°C - 12-15 weeks, and at 3-5°C - 163 days, and alcohol at the end fermentation was 5% vol.

Porsche, observing the storage of fruit juices, found that yeast can ferment at 0°C and even at -3°C. The author emphasizes that carrying out alcoholic fermentation at a temperature below 15°C excludes the development of malolactic fermentation, which is very important in the production of red and highly acidic white wines.

Joslin points out that the temperature of fermentation should not exceed 27°C, and for the production of wines of the highest quality 21°C. Wine material going for distillation should not have a fermentation temperature above 30°C.

According to Gerasimov, the fermentation of the must at temperatures below 16 ° C is very sluggish. However, if it has already begun at an elevated temperature (above 20°C), lowering the temperature of the fermenting wort does not affect the vital activity of the yeast as sharply as at the beginning of fermentation. At temperatures above 35°C, the yeast experience strong inhibition, and at 40°C they completely stop their activity. The temperature optimum for the development of yeast lies in the range of 22-30°C. The minimum temperature at which yeast retains its vital activity is -8 ° C.

The maximum temperature of the fermenting wort observed in Turkmenistan was 40-42°C. This temperature inhibits the fermentation ability of yeast, which is due to changes in the intracellular structure, leading to cell death. Local Turkmen yeasts are more thermostable and easily endure temperatures up to 40°C. At 41-42°C, these yeasts can ferment sugar to the end only if the initial sugar content of the wort is not more than 20%. For normal fermentation of high-sugar wort in the conditions of Turkmenistan, the temperature should not exceed 37°C.

Moser, carrying out fermentation at temperatures below 15 ° C, found that the resulting wines are much better in organoleptic qualities and in the development of the bouquet than wines fermented at temperatures above 25 ° C. This is especially evident in highly aromatic varieties, such as Muscat.

Other researchers have successfully carried out fermentation at low temperatures.

Many experts attach particular importance to the uniformity of the fermentation temperature, that is, to such a regime in which the temperature deviates from the set temperature by no more than ± 2 ° C. However, this seems to be based on impressions and not on exact experimental data. The main point here is the behavior of yeast, i.e., the identification of the thermal parameters of their reproduction and death. In this regard, there are critical points, and a deviation from them even by 1-2°C causes a sharp change in the state of the yeast. In other temperature ranges, a deviation of even 10°C will not cause noticeable changes in the vital activity of yeast, but can dramatically affect the chemical composition of the resulting wine materials and, above all, the content of nitrogenous substances in them.

There are a number of patents on methods for automatically regulating fermentation, which is carried out either by the temperature of the fermenting wort, or by the carbon dioxide released, or by the course of sugar decomposition.

Fermentation experiments at various temperatures were carried out by A. A. Preobrazhensky and other researchers. The results of these experiments confirm the well-known data that at elevated fermentation temperatures, the yeast dies off and pedobrods can be obtained. At low temperatures, the fermentation period is delayed.

One of the main factors determining the quality of table wine is the harmonious content of grape essential oils, aldehydes, volatile acids, organic acids, nitrogenous substances, especially amine nitrogen, enzymes and some other substances.

The pH of the medium in which the yeast is cultivated, the fermentation temperature and the degree of aeration of the fermenting must have a great influence on the course of metabolism, on the production and activity of enzymes.

Volatile acids are formed by yeast in small amounts in an acidic environment. An increase in the pH of the medium leads to a more enhanced formation of volatile acids, which is the result of the action of the yeast enzyme apparatus that regulates the pH and keeps it at an optimal level for yeast development.

Yeast, reacting to a change in the environment in an unfavorable direction for their life, try to eliminate this shift. So, when the pH rises above the optimal value, they form an increased amount of acetic acid, and the more, the higher the pH.

The lowest content of volatile acids is observed at pH ranging from 3 to 4. In an alkaline environment, acetic acid is formed in significant quantities and at all stages of fermentation at an almost constant rate. It has been established that at pH 3 volatile acids contain a minimum amount, while the strength reaches a maximum. Yeast also reacts to changes in temperature and degree of aeration of the fermenting medium, forming different amounts of certain substances. The least volatile acids are obtained at a fermentation temperature of 15 to 25°C. Increasing the fermentation temperature above 25°C and lowering it below 15°C leads to an increased formation of volatile acids during the fermentation of grape must. The effect of fermentation temperature of sterile wort on the formation of volatile acids is shown in Table. 17.

In the wort, fermenting with the access of atmospheric oxygen, at all temperature options, even slightly less volatile acids are formed than in control samples fermenting under anaerobic conditions. However, the general pattern of increasing the content of volatile acids at low and high temperatures remains. This is evidenced by the data in Table. eighteen .

Must and wine are characterized by a significant content of nitrogenous substances represented by proteins and their hydrolysis products: peptones, peptides, amino acids, as well as amides and ammonia. The importance of nitrogenous compounds at the stages of formation and formation of wine is beyond doubt. On the one hand, they are essential nutrient material for yeast during alcoholic fermentation and for bacteria during malolactic fermentation; on the other hand, some substances have a direct or indirect effect on the addition of aromatic and gustatory qualities of wine in the process of its formation and maturation.

An excess of nitrogenous substances, under certain conditions, creates the preconditions for a greater tendency of wines to turbidity and microbial diseases, and in the presence of oxygen access to them - to overoxidation and maderization.

Substantiation of methods for regulating the amount of nitrogenous substances in wine materials is an important practical task.

One way to reduce the content of nitrogenous substances in the wine material is the so-called biological nitrogen reduction. But, according to E. N. Datunashvili, even sevenfold filtration with the addition of a fresh portion of yeast after each filtration does not remove all the nitrogen assimilated by the yeast. In addition, the implementation of this technique in a production environment is very difficult.

An excellent regulator of the content of nitrogenous substances in wine materials is the temperature of fermentation. Carrying out fermentation at a temperature in the range of 14-18 ° C, it is possible to obtain wine material with a minimum content of nitrogenous substances. An increase in the fermentation temperature causes an increase in the amount of nitrogenous substances and, above all, amine nitrogen as a result of the death and autolysis of yeast cells. With a decrease in the fermentation temperature (10 ° C and below), the content of nitrogenous substances also increases. And if in the first case (at high temperature) this increase in the amount of nitrogen occurs due to low molecular weight compounds - peptides and amino acids released by yeast cells as a result of autolysis, then at low temperature nitrogen is probably represented by high molecular weight compounds - polypeptides, peptones and proteins (Fig. .19 and table 19) .

Note. The fermentation of the pasteurized wort was carried out on the Steinberg 1892 yeast race.

Based on the balance of nitrogenous substances consumed by yeast and released back into the medium at different fermentation temperatures, we found that during the fermentation of grape must, the most uniform consumption of nitrogenous substances is observed at 15°C. At this temperature, throughout the entire fermentation, the release of nitrogenous substances by yeast cells is not analytically detected. Obviously, it still occurs, but the consumption of nitrogenous substances by yeast significantly prevails over their excretion (Fig. 20).

When the temperature of the fermenting medium is 25-30°C, the consumption of wort nitrogen by yeast is more intensive, since due to favorable conditions, the yeast multiply intensively and their number increases over a certain period. At the end of fermentation, even in the presence of residual sugar, the yeast begins to release nitrogen to the same extent into the fermenting medium due to the autolysis process that has begun.

At low fermentation temperatures, yeast consumes significantly less than the initial must nitrogen, since the conditions for yeast reproduction at 5-10°C are unfavorable and their mass is less. And this mass of yeast takes a smaller amount of nitrogenous substances from the wort to build their cells. Therefore, after fermentation at low temperatures in the wine material, the content of nitrogenous substances increases due to the underutilized nitrogen of the must.

As mentioned, the regulation of the fermentation temperature and the establishment of accurate thermal parameters for the fermentation of certain types of wines allow you to increase or decrease the concentration of nitrogenous substances in the wine material by 2 times or more. It was also found that light aeration in the first half of fermentation can significantly reduce the amount of nitrogenous substances in wine materials. The dependence of the content of nitrogenous substances in the wine material on the degree of aeration of the fermenting must (initial must nitrogen, mg / l: total - 552, amine - 324, protein - 102) is shown in Table. twenty.

Notes: 1. Fermentation of pasteurized wort was carried out on the Feodosia I-19 race. 2. Initial nitrogen of the must: total - 552 mg/l, amine - 324 mg/l, protein - 102 mg/l.

On the basis of the data obtained, a method for regulating the content of nitrogenous substances in the wine material was proposed by regulating the temperature of fermentation and aeration of the fermenting must. This method makes it possible to regulate the nitrogen content in the wine material both quantitatively and qualitatively. For example, at a fermentation temperature of 15°C and light aeration, wines containing about 100 mg/l of total and about 50 mg/l of amine nitrogen can be obtained, and at high and low temperatures without aeration - 200-250 mg/l of total nitrogen, and at 10°C, these will be mainly high-molecular nitrogenous compounds, and at high temperature, amino acids and peptides.

The titratable acidity of young wine materials depends on the fermentation temperature. The lower the fermentation temperature, the lower the titratable acidity, and vice versa.

The titratable acidity of the wine material is also influenced by the race of yeast on which fermentation is carried out. In the first half of fermentation, an increase in the titratable acidity of the must is observed. At low and high temperatures in the second half of fermentation, there is a gradual decrease in the titratable acidity of the fermenting medium. At 15°C, the titratable acidity in the second half of fermentation hardly changes.

Such a difference in the content of titratable acidity in wine materials obtained at different temperatures is probably due to the fact that the bulk of organic acids that occur during fermentation are formed by young yeast.

It has been established that at 15°C yeast multiplies throughout the fermentation, and consequently, new acids are formed all the time.

At 10°C, along with the fact that throughout the fermentation there is a multiplication of yeast and new formation of acids, there is an increased precipitation of cream of tartar caused by low temperature.

At 25°C, in the second half of fermentation, the reproduction of yeast is sharply reduced, the death of yeast cells and their autolysis begins. The purine bases and basic amino acids released as a result of autolysis may also reduce the titratable acidity (most amino acids, as amphoteric compounds, play the role of bases in wine).

When wine is clarified after fermentation, the titratable acidity of young wine material decreases at all aging temperatures.

When fermented in reinforced concrete tanks without special coatings, wine materials have a titratable acidity lower than wine materials fermented in barrels. This is due to the fact that tartar settles better on the rough surface of the tank walls.

For fermentation of vintage white table and champagne wine materials, a temperature regime of 14-18 ° C is recommended. At these fermentation temperatures, the minimum content of nitrogenous substances and, above all, amine nitrogen is obtained in wine materials.

One of the significant reasons for the decline in the quality of table wines is their tendency to overoxidize, i.e., to acquire specific shades of wine in taste, bouquet and color. Free oxygen cannot have such an effect, only its interaction with some other substances leads to over-oxidation of wine.

V. I. Nilov believes that as a result of the interaction of oxygen with the components of wine, and especially with nitrogenous substances, in particular with amino acids, on the one hand, aldehydes are formed, which, depending on the composition of the amino acids, can determine the tone of maderization and its various shades, with on the other hand, in the course of deamination of amino acids, ammonia is formed, the salts of which, at a certain concentration, impart disorder and roughness to the wine.

How the chemical process proceeds can be seen from the following formula:

First, the amino acid, losing two hydrogen atoms, passes into an imino acid, which, decomposing and releasing CO 2, forms aldimine, the latter, when saponified, gives ammonia and aldehyde, containing one carbon less in its molecule than the original amino acid. This process can occur with the participation of catalysts (Fe .., Cu . , Mn ..) and with particular intensity at elevated temperatures. As a result, the main products that determine the tone of overoxidation are aldehydes and ammonia.

At a fermentation temperature of 14-18°C, the least amount of volatile acids is obtained in wine materials, which is not organoleptically noted, but, of course, this will have a positive effect in the future when the wine matures.

At relatively low temperatures of 14-18°C, 2-3 times less aldehydes are formed than at high temperatures, which is especially important in the manufacture of champagne wine materials.

The duration of fermentation increases slightly and is 9-10 days instead of 5-6, while at a temperature of 10 ° C, the fermentation period increases to 20 days, and sometimes more.

The consumption of cold to maintain the temperature regime of fermentation 14-18°C is relatively small (125-150 kcal/dal wort). To maintain the temperature regime of fermentation of 9-12 ° C cold, it is required to spend 2 times more.

In production experiments conducted by us for 4 years on grapes of different varieties, there has never been a noticeable improvement in the quality of wine materials fermented at 10°C compared to wine materials fermented at 14-18°C. Quality improvement by 0.1-0.2 points does not justify the cost of maintaining this mode. However, it is impossible to completely abandon the fermentation regimes at 10 ° C and below. The fact that at these fermentation temperatures, together with CO 2, the least aromatic substances are removed and the most aromatic wines are obtained, makes it necessary to carefully study the behavior of grapes of individual varieties at a fermentation temperature of 10 ° C and below.

With complete fermentation of 1 liter of wort with different sugar content, the following amount of heat is released:

A significant part of the heat is lost through the walls of the fermentation tanks and carried away with CO 2 . The size of heat loss depends on the surface, the thermal conductivity of the material from which the container is made (for steel it is 39, and for wood - about 0.2), container volume, ambient temperature, fermentation intensity and other factors.

According to A. M. Frolov-Bagreev, during fermentation on pulp in a vat with a capacity of 600 dal, the heat loss is 60% of the heat released during the fermentation process, and for vats with a capacity of 3000 dal - only 25%.

In barrels with a capacity of 20 dal, the fermentation temperature can rise at an ambient temperature of 15 ° C by 3 °, in barrels of 25 dal - by 4 ° and in barrels of 50 dal - by 6-8 °. At higher ambient temperatures, the temperature of the fermenting wort will be even higher.

Heat loss will be the greater, the smaller the capacity of the tank, the larger its surface in relation to the volume, the slower fermentation, the lower the ambient temperature, the thinner the walls of the vessels and the higher the thermal conductivity of the material. A significant part of the heat is removed with water vapor, which is carried out with fermentation carbon dioxide.

In wooden bottles per 100 dal, the temperature during fermentation can rise by 6-8 °. So, if the initial temperature of the wort is 15-18°C, then during fermentation it rises to 22-25°C. In large reinforced concrete tanks with a capacity of 3000 dal the temperature reaches 36-38°C.

Müller-Thurgau observed the following maximum fermentation temperatures in wooden butes placed in a cellar at 13°C:

In the experiments, the loss of heat during fermentation in tanks with a capacity of 3500 dl without artificial cooling ranged from 30 to 60%, depending on the rate of fermentation (from 40 to 70 h). The temperature of the fermenting wort rose respectively by 18°C (with a loss of 30% of heat) and by 9°C (with a loss of 60% of heat).

If fermentation takes place in small vessels, such as barrels, then the temperature is controlled by heat radiation through the walls of the vessel (Fig. 21).

In large reinforced concrete tanks, heat transfer will not provide a normal fermentation temperature. The larger the tank capacity, the higher the fermentation temperature will be.

There is the following dependence of the fermentation temperature on the size of the reservoir (Table 21).

Therefore, it is absolutely necessary to carry out the cooling of the fermenting wort during fermentation in large containers.