Types of yeast, features of working with them, tips for working with yeast and all sorts of tricks
Yeast are unicellular organisms belonging to the fungi family.
"Wild" yeast is everywhere, including in the air. They feed, produce energy, produce by-products, reproduce. Yeast feeds on sugars, and in their absence, they break down starches. by-product The vital activity of yeast is carbon dioxide, which is released in the form of tiny bubbles. These bubbles "get stuck" in the gluten framework, and give us the mesh structure of the dough when baking.
When gas accumulates (or when heated), the bubbles increase in size and rise to the top. Together with them, the dough also rises. This is what is meant when they say that the dough is suitable.
Yeast operates under both aerobic and anaerobic conditions. Aerobic conditions require access to oxygen. In the process of aerobic respiration, yeast produces a lot of energy, releases carbon dioxide and reproduces. Under anaerobic conditions, access to oxygen is minimal, so the yeast produces much less energy, emits much less carbon dioxide, and produces alcohol and various acids. With a small amount of oxygen, yeast reproduction is also minimal. This process is called fermentation.
The dough is a closed system in which yeast lives, feeds, reproduces and dies. Their rate of reproduction depends on the temperature and the amount of food (sugars) available. At high temperatures (30–35 degrees and above), the reproduction rate increases, at low temperatures it decreases. Another factor that slows down the rate of yeast reproduction is the salinity of the environment. In addition, the waste products of yeast (carbon dioxide, alcohol, etc.) also slow down the rate of their reproduction.
Yeast reproduces by cell division. One cell is capable of dividing 20–25 times, that is, creating from 20 to 25 new cells. The lifespan of one generation ranges from one to seven hours, depending on the environment and the age of the mother cell.
Dough proofing
The purpose of dough proofing is to stretch the web of gluten with the help of bubbles of carbon dioxide released by the yeast. Thanks to these bubbles, which increase in size and try to rise to the top, the dough “swells” in volume and becomes elastic. Smell and taste also depend on this process.
First proofing
Yeast activity in dough is subject to rapid change. Initially, during the first kneading and first proofing, the yeast is in an aerobic state, there is a lot of oxygen and nutrients around it, and there is relatively little yeast. They multiply at a fast pace (this depends mainly on the initial amount of yeast, salt and sugar in the dough and temperature). The dough can be baked after the first proofing, but then it will be inelastic, and its pores will be inhomogeneous.
Second proofing
Over time, conditions change: there are fewer nutrients and oxygen - oxygen is displaced by carbon dioxide, which slows down the process of yeast reproduction. True, there are now many more of them in the test, but they do not multiply. In order to cause a second fermentation (i.e., so that the dough comes up a second time), it is necessary to recreate the conditions for aerobic activity. To do this, carbon dioxide should be removed from the risen dough, replacing it with fresh oxygen. To achieve this, the dough is kneaded with hands starting from the center and passing over the entire surface. The goal is to allow fresh oxygen to enter the dough so that the yeast can continue its activity and spread evenly throughout the dough. In addition, thanks to this action, the gluten network remains tense and elastic.
As a rule, the second proofing is faster, because the dough has a lot more yeast and a much higher amount of carbon dioxide released. The dough, which is baked after the second proofing, has an elastic structure and a richer taste and aroma. Its pores are uniform, and their size depends on the amount of water added to the dough.
It's important to know
Increasing the yeast content in the dough (say, twice) will not lead to the same increase in the rate of fermentation - both due to the competition of yeast for available resources (oxygen and sugars), and because the more yeast, the more carbon dioxide they produce, and it slows down their activity.
Water speeds up yeast activity. It helps them move freely through the dough, dissolves nutrients and promotes their enzymatic activity. If there is a lot of water in the dough, it activates the yeast, and then the dough fits better, and its pores become larger and more beautiful. When fats or sugar are added to the dough, and in order to compensate for changes in its texture, the amount of water is reduced, this interferes with the activity of yeast.
A change in temperature can speed up or slow down the rate of fermentation (outside of yeast propagation, which requires the presence of oxygen). Fermentation rate at 30 degrees is three times faster than at 20 degrees, but fermentation rate at 40 degrees is only twice as fast as at 30 degrees. At temperatures above 50 degrees, fermentation stops. At a temperature of 0 degrees, yeast activity also stops. Yeast can survive freezing, but only if it happens quickly enough. Slow freezing can damage cell structure. french bakers It is believed that the dough is best suited at 27 degrees. At this temperature, the rate of gas evolution is quite high - the dough is of excellent quality, and the bread from it is very tasty and fragrant. At a temperature of 35 degrees, the dough rises faster, but bitter components are released that affect the taste; in addition, the dough becomes more viscous.
Types of yeast
Baker's yeast is grown in an oxygen-rich environment, in special containers with sugar beets, nitrogen mixtures and minerals. These fungi appear as a foamy coating, which is cleaned of impurities using a centrifuge and water. Then the resulting material is dehydrated, compacted and sold in this form.
Fresh yeast (cubes)
They are an accumulation of yeast cells isolated from the culture medium, washed and compressed. This is the so-called domestic pressed yeast, familiar to many for a long time. AT retail they are available in bars weighing 50 and 100 g.
When baking bread, they are most often used, as they create perfect taste and invoice. The moisture content of fresh yeast is about 70%. Of the commercially available yeast, this type provides the strongest fermentation. Currently, you can buy imported pressed yeast in stores. They have more activity than domestic ones (the lifting force of imported yeast is 30-35 minutes, and domestic yeast is about 70 - this is the time it takes to raise the dough to 70 mm), so they need to be put into the dough 1.7-2 times less than domestically produced pressed yeast.
At room temperature such yeast is stored for no more than a day. In the refrigerator from 0 to +4°C, up to 12 days.
If fresh yeast has winded up, you can try to “reanimate” it: grind it in a spoon warm water with the addition of 1 tsp. Sahara. If after 10 minutes the yeast starts to bubble, it means that they have “come to life”. Dark dry pieces should be thrown away without regret. And at the same time, reconstituted yeast should be taken twice as much as fresh.
Dried active yeast
They are also activ dry yeast or cake yeast or compressed yeast in the form of vermicelli, granules or grains obtained by drying crushed pressed yeast. Dried yeast granules are protected from atmospheric oxygen by a natural protective layer of dead yeast cells that forms during the drying process.
Before being added to the dough, dried yeast needs to be rehydrated, i.e. they need to be dissolved in water. During the drying process, the yeast cell membrane becomes porous and vulnerable, and therefore dry yeast must be dissolved carefully and carefully, observing certain conditions, namely: 5 parts of water are added to 1 part of yeast ( optimum temperature water - 35–38°C) and let stand for 10–15 minutes, during which time the yeast is not stirred due to the risk of damaging the cell membrane, and then gently stirred. Usually active yeast require confirmation of activity. To do this, a little flour and (or) sugar is added to the yeast solution and left warm for 10-15 minutes. If the yeast is alive, they form a beautiful foam cap; if there is no cap, the yeast, alas, has lost its activity and needs to be replaced.
Dried active yeast "Saf-Levure" has a high enzymatic activity and in the dough they need 4-5 times less than domestic pressed baker's yeast or 2 times less than fresh imported ones.
Open yeast in the form of granules can be stored in the refrigerator for about six weeks at a temperature below 10 degrees.
Fast acting (or instant) yeast
Either instant yeast or fast rising / rapid rise / quick rise or bread machin yeast have been known since the late 60s, they were created based on new yeast cultures using progressive drying methods and emulsifiers. Instant yeast does not require pre-soaking and is added directly to flour or freshly kneaded dough. Instant yeast is more microbiologically pure than dry yeast and even pressed yeast. Instant yeast is added to the dough 5-6 times less than domestic pressed ones.
The required amount of yeast is usually prescribed in the recipe and depends on the following factors: the lifting power of the yeast (the higher it is, the less yeast is needed), the duration of the fermentation process (with a longer fermentation time, less yeast is required), the method of preparing the dough (spared requires less yeast, unpaired more), sugar and fat content in the dough (the higher, the more yeast is needed).
You can not mix salt directly with yeast (and also add it to the yeast solution). Relatively high concentration salt neutralizes yeast. Salt is added at the very end, when all the ingredients are already in the dough. Then its percentage is small, and this will not interfere with the yeast.
Although the packaging fresh yeast it is indicated that the recommended amount of yeast is 50 g per kilogram of flour, it is better to put them in half (25–30 g per kilogram). By doubling the portion of yeast, we will not make the dough rise twice as fast. Moreover, it can give the product an undesirable aftertaste.
Make sure you get the prescription from a trusted source. Carefully observe the proportions indicated in it. Do not add flour to the dough, even if it looks too wet and sticky. A long and vigorous kneading will allow the gluten to absorb the liquid and develop well. A large amount of water is necessary for the normal activity of the yeast. If you add flour, the dough will become denser and less tasty.
The dough is best suited at a temperature of 27 degrees. At too high a temperature, it will acquire a bitter taste.
Do not use the oven or microwave to increase the fermentation temperature, artificially forcing this process may affect the aroma and texture of the baked goods. Therefore, if there is time, the usual, "natural" process is recommended. Using an oven or microwave can bring temperatures up to 50 degrees or more in some places, causing irreparable harm yeast, and consequently - the volume and texture of bread. Room temperature is sufficient for proofing.
The dough needs to rise for at least two and a half to three hours (yeast cell division time) for the total amount of yeast in the dough to double. Yes, it is possible to increase the rate of yeast reproduction, but in the manufacture of bread, organic mixtures are also of no small importance, which form slowly and give finished product rich taste and aroma.
The first proofing of the dough (under optimal conditions) should last about an hour so that the yeast “eats” the entire supply of sugars and begins to break down the starch.
Formula for transferring different types of yeast according to the recipe
Amount of fresh yeast * 0.41 = amount of dry
Amount of dry * 2.42 = Amount of fresh
50 g fresh yeast ≈ 20 g dry (or 2 tbsp flush with the edges) ≈ 50 g granulated (4 tbsp)
What is yeast and how does it work was last modified: March 27th, 2017 by dimabuko
Which have lost their mycelial structure, because their habitats have become substrates of liquid or semi-liquid consistency, containing a large amount of organic matter. The group of yeast fungi includes 1500 species that belong to the classes of Basidiomycetes and Ascomycetes.
In nature, yeasts are widely distributed and live on substrates rich in sugars, feeding on flower nectar, plant sap, dead phytomass, etc. yeast mushrooms can live in soil and water, in the intestines of animals.
Yeasts are fungi that live during all or most of their life cycle in the form of individual single cells. Yeast cells are on average 3 to 7 microns in diameter, but there are some species whose cells can reach 40 microns. Yeast cells are immobile and have oval shape. Although yeast does not form mycelium, they have all the signs and properties of fungi. Yeast fungi are organotrophic eukaryotes with absorptive nutrition. These fungi use organic matter to obtain carbon and the energy necessary for life. Yeast needs oxygen for respiration, but in the absence of its access, many types of facultative anaerobes of yeast fungi obtain energy as a result of fermentation with the formation of alcohols. Yeast fermentation stops or stops completely if oxygen begins to flow to the fermented substrate, since respiration is a more efficient process for obtaining energy. But if the concentration of sugars in the nutrient medium is very high, then even with the access of oxygen, the processes of respiration and fermentation are carried out simultaneously. Yeast fungi are very demanding on nutritional conditions. In an anaerobic environment, yeast assimilate only glucose, while in an aerobic environment they can also use hydrocarbons, fats, aromatic compounds, organic acids, and alcohols as energy sources.
The growth and reproduction of yeast occurs at a tremendous speed, while provoking characteristic changes in the environment. So, thanks to the process of alcoholic fermentation, yeast has become widespread throughout the world. Yeast is believed to be the oldest of the plants cultivated by man. Reproduction of yeast is carried out by budding (division). Sexual reproduction is also possible. In this case, the resulting zygote is transformed into a "bag" in which 4-8 spores are enclosed. In the unicellular state, yeasts are capable of vegetative reproduction. So, spores or zygotes can bud. The division of yeast into groups (classes Ascomycetes or Basidiomycetes) is based on the methods of their sexual reproduction. There are types of yeast that do not have sexual reproduction. Their scientists included in the class of imperfect fungi (Fungi Imperfecti, or Deuteromycetes).
Certain types of yeast have been used by man since ancient times in the manufacture of wine, beer, bread, kvass, in the industrial production of alcohol, etc. Some types of yeast are used in biotechnology due to their important physiological features. In modern production, using yeast, get nutritional supplements, enzymes, xylitol, purify water from oil pollution. But there is also negative properties yeast. Some types of yeast can cause disease in humans, as they are facultative or opportunistic pathogens. Such diseases include candidiasis, cryptococcosis, pitiriasis.
The kingdom of mushrooms is one of the most unusual and impressive in the world of wildlife. The diversity of these organisms is really impressive, and their properties are worthy of careful study. People encounter some of their species every day, without even thinking about the fact that these are mushrooms. It is on such varieties that it is worth dwelling in more detail.
What are mushrooms?
This kingdom has a complex classification. Most people understand only one type of mushrooms, the main one is hat. It includes both edible and poisonous options - champignons, truffles, mushrooms, chanterelles, fly agarics, grebes and many others.
Another, even more interesting species are fungi. They are microscopic in size, due to which the fruiting bodies and mycelium are almost impossible to notice with the naked eye. But in general, it is not at all difficult to see them - just leave a piece of bread in a humid place, and soon a familiar fluffy coating will appear on it. These are mold fungi, namely saprophytes, an inedible species that often spreads through fruits, vegetables, soil and walls of damp dark rooms.
The third type is yeast. They have been known to man for a long time and are as common as mold fungi. For example, it is to them that people owe the existence of bread, beer, wine and kvass. Molds and yeasts reproduce equally well in the everyday human environment, but, unlike the former, which prefer dampness and twilight, the latter need sugar. But there is one thing in common - yeast is also impossible to see in detail without a microscope. To date, a person knows 1500 of their varieties.
yeast mushrooms
This species differs from all others in that it has lost the mycelial structure classic for the kingdom. Yeast lives in a liquid or semi-liquid medium filled with organic matter. They exist as dividing or budding cells. This structure allows them to have maximum high speed metabolism, so they can grow and multiply quickly. Although molds and yeasts seem similar due to their microscopic size, the former still have mycelium and all the characteristic features, while the latter are one cell. The history of the origin of the name of this variety is interesting. The word "yeast" refers to the trembling that can be seen in fermented wort or rising dough.
Features of mold fungi
This variety retains most of the properties of cap species. However, they are microscopic in size. Mold fungi form the thinnest branched mycelium, from which large fruiting bodies are not separated. They were the first inhabitants of the planet Earth, on which they appeared more than two hundred million years ago. The mycelium of the mold fungus develops in almost all conditions in nature, regardless of the availability of food and the characteristics of the habitat. Huge colonies instantly appear in the presence of humidity and a sufficiently high temperature.
The types of mold fungi are very numerous, but they have common features - the mycelium serves as the basis, and thin branching filaments are placed right inside the affected surface. Unlike yeast, they reproduce sexually or vegetatively. The mold cell does not make up its entire body. However, this does not prevent them from spreading at a tremendous speed.
The most famous fungi
Some of the representatives of the kingdom are more important to humanity than others. These are penicillium molds, which are green spots that grow on plant substrates and common foods. They produce an antibiotic called penicillin, which was the world's first antibacterial drug. His invention changed the world of medicine. Both molds and bacteria can be harmful to human health. But a species called penicillium can save lives, which has earned its widest fame.
Phycomycetes class
One of the most common species are Phycomycetes, or mucor molds. There are more than three hundred varieties in this family. The three most common are Mucor, Thamnidium and Rhizopus. The structure of mold fungi mukor differs in that their mycelium often consists of a single branched cell. Aerial spherical hyphae filled with many spores depart from it. The spread of mucoral occurs easily and quickly on many types of substrate, with the exception of dairy products, and stops only at temperatures below -8 degrees Celsius.
Ascomycetes class
It is to this family that penicillium fungi belong, as well as some others, for example, the genus Aspergillus. Otherwise, this class is called marsupials. While mucor molds form a primitive unicellular mycelium, ascomycetes are distinguished by a more complex structure, which quickly forms separate colonies that grow along the substrate. Spores are instantly formed on it, to which the mold owes its fluffy appearance of a grayish-green color. When studied under a microscope, the reasons for the name become obvious - the structure of molds includes long chains of conidia containing spores, which form a brush or bag. Ideal conditions for development are dampness and poor ventilation at temperatures close to 0 degrees Celsius.
Difference Aspergillus from Penicillum
Found in the same family, these molds are similar in appearance. They have a colorless mycelium with colored spherical conidia, as a rule, they are distinguished by a grayish-blue or gray-green tint, less often with a yellow undertone. However, the role of aspergillus molds is markedly different. While penicillin is an important component medicines, in a form related to penicillium, contains substances that cause spoilage of dairy or meat products.
imperfect mushrooms
This class has not been studied as extensively as those described above. Imperfect mold species reproduce by a method other than sexual reproduction, not known in detail. They are distinguished by septate mycelium with grape-like spores of dark color. Because of this, the defeat of such mushrooms forms black velvety spots. This mold develops well with low temperatures and is distinguished by a large affected area - when it appears on meat, it penetrates deep into the muscle tissue. It is these fungi that can lead to internal mold, spoil butter, cheese, egg products.
milk mold
Mushrooms of the variety Oidium lactis resemble yeast in their structure. They have a white septate mycelium with separated spores in the form of single cells. The nutrition of molds of this species includes a variety of dairy products. Their appearance is manifested in the form of a fluffy white coating, which can cover the surface of sour cream, curdled milk or cottage cheese. Mold reduces their acidity, causing the product to deteriorate. Some scientists attribute them to yeast due to the simplicity of cell chains and felt-like mycelium.
Mold that grows in the refrigerator
Several varieties of fungi can affect products that are stored at a sufficiently low temperature. First of all, this is Botrytis, which is distinguished by its creeping mycelium felt-like different kind, with colorless conidia appearing in tufts. Molds also include those that are distinguished by brown or olive conidiophores. A similar species develops in the refrigerator at temperatures below 5 degrees Celsius and affects a variety of products. Another dangerous species to eat is Alternaria. These include mushrooms with pear-shaped or pointed conidia of brown or olive color. Such mold can infect not only chilled, but also frozen meat, as well as butter and other food products.
Thomas class
These molds differ from all others in their original structure. They do not form an external mycelium and most often develop inside the substrate, which is undergoing a decay process. To reproduce, Phoma molds use short conidiophores with intertwined hyphae surrounding them like a shell.
How does mold affect the human body?
Not all types of mushrooms are as useful for humanity as penicillium. More often, the situation is quite the opposite, and the appearance of mold is an unkind sign. First of all, its spores have a very negative effect on the mucous membranes of the body, causing immune reactions. This is one of the strongest allergens, and people with certain problems in this area are guaranteed to be uncomfortable at the slightest contact with mold. And it's not just a short-term reaction - over time, everything can end in serious diseases. In houses affected by molds, eight out of ten tenants develop asthma. The number is very impressive. And this is not all possible problems.
If such a problem arises, it is necessary to think about ways to destroy mushrooms as soon as possible. To do this, you should use a special antiseptic, which can be purchased at a building materials store. It is necessary to work with it as carefully as possible, having studied the instructions for use. In addition, before starting the fight against mold, it is worth examining how deeply the surface is affected. Sometimes it is better to throw away an infected item. If the defeat is not so large-scale, you can proceed to action. First of all, pay attention to the antiseptic primer. It will not only kill the mold, but also prevent its reappearance. Using such a tool is quite simple, most often you do not even need to dilute it with water. It is only recommended to clean the surface before treatment.
If there is no opportunity or desire to look for a special remedy, you should turn to home methods. For example, great option may be bleach. The sodium hypochlorite contained in it kills not only mold, but also its spores. Bleach is ideal for when you need to clean bathroom tiles, floors or glass. But for other items, it can be dangerous - many things lose color or deteriorate from such processing. In addition, bleach is quite toxic, so you should only use it in a well-ventilated room, armed with protective rubber gloves.
Vinegar is less dangerous in such cases. It is not so toxic, so it can be used without fear. It is worth using vinegar with a spray bottle or by wetting a rag in it and wiping the surface affected by mold.
For those who do not have such a tool in their arsenal, hydrogen peroxide is suitable. It can be bought at any pharmacy, it is not dangerous to health and does not have a pungent odor. Peroxide can kill mold on a wide variety of surfaces, but be aware of its bleaching effect, which can be harmful to fabrics or paints.
For hard surfaces like tiles and glass, ammonia is also suitable. It is enough to mix it with water in equal proportions and spray the mixture over the entire infected area, and rinse it with water after a few hours.
by the most safe means becomes baking soda. It will not harm family members or pets. To combat mold, a teaspoon of soda is dissolved in a glass of water, after which the affected surfaces can be sprayed with the mixture. It is not necessary to wash off the solution - it will be a prophylactic.
Yeast is a collective group of fungi that do not have a typical mycelium and exist in the form of separate budding or dividing cells.
Yeasts are fungi that exist throughout the entire life cycle or most of it in the form of separate single cells. Due to their unicellular structure, yeasts have a higher metabolic rate than filamentous fungi due to their relatively larger area cell surfaces. Yeast grows and reproduces at a high rate, causing significant changes in the environment. Historically, yeasts have always been considered separately from other fungi, since the methods of their study are more similar to bacteriological than to mycological.
Yeast-like stages are found in various groups of fungi, not only in the Saccharomycetaceae family. Based on the method of sexual reproduction, yeast is divided into groups located in different classes of fungi - marsupial and basidial, and yeast in which the sexual cycle is not found is classified as imperfect fungi (deuteromycetes). Thus, yeast is not a taxonomic, but rather a biotechnological term. There are no phytopathogenic species in the Saccharomycetaceae family; all saccharomycete yeasts are saprotrophs.
The body of yeast is very different from that of most fungi, as it consists of only one cell and therefore does not form mycelium. For the first time they were examined under a microscope by the Dutch scientist Leeuwenhoek. However, his contemporaries did not understand the significance of this discovery, and it took about 150 years for scientists to understand the essence of these microorganisms and classify them as fungi.
Meanwhile, mankind has long used yeast to make alcoholic beverages and in bakery. Archaeological excavations in Egypt and ancient Babylon have discovered the remains of breweries and bakeries that were built almost 6 thousand years before the new era. According to ancient Greek legends, the god Dionysus gave people the art of making wine.
In many languages, the name of yeast refers to the fermentation process it causes. Them Russian name comes from the word tremble, tremble, which characterize the state of fermenting wort or rising dough.
For the first time, the connection between fermentation and yeast was scientifically explained by the founder of microbiology, L. Pasteur. He established that fermentation replaces respiration for yeast. His saying is known: "Fermentation is life without air."
Yeast reproduction is very original: a small protrusion appears on the cell, it grows (it turns out to be a kidney) and finally turns into an independent cell and can separate. This process is called yeast budding.
About 500 types of yeast are known in nature. We come across many of them in everyday life. Yeast is divided into baker's, beer and wine. In baking, for example when we bake pies. We use yeast to make the dough rise. Yeast is used in winemaking, where the fermentation process is necessary. Great importance has the use of yeast in brewing.
Yeast has always been the constant companions and friends of man.
It is interesting
About a hundred years ago, at the foot of Elbrus, in the villages of the highlanders-Karachays, there was a custom. A leather waterskin filled with milk was thrown out into the street and left to lie there for some time. Everyone who passed by had to kick the wineskin with his foot. The boys especially liked this procedure. They rolled him on the ground, kicked him, mounted him. Physical exercises were prescribed to the wineskin not by chance. In addition to milk, sourdough was also placed in it - kefir "grains". When the waterskin was kicked, the fermenting liquid was agitated. The curdled milk became homogeneous.
In those years, the world did not yet know kefir. Only the mountaineers knew. They did not disclose the secret of kefir "grains". This is what religion required. However, no secret is eternal. Little by little, information began to leak out, and gradually they got acquainted with kefir, first in Russia, and then all over the world. A craze for a fashionable drink began, which has not ended to this day.
Several stories are told related to the disclosure of the secret. There are horse racing, chasing and kidnapping beauties. It seemed to me more plausible version of the Cossack N. Sigalova from the village of Krymskaya, which she described in a small book at the end of the century.
At the insistence of doctors, Sigalova was forced to leave her native places and go to the waters in Pyatigorsk for the treatment of a severe pulmonary disease. Changing places did not bring the desired result. The unfortunate woman had already completely lost hope for healing when she met the highlanders who had come to the market in Pyatigorsk. I learned from them that in the villages they treat lung diseases with kefir. The highlanders told something, but they refused to bring a drink: it is forbidden by the Koran.
Now, if the Russian herself went to the village ...
There was no choice, and Sigalova went to Budukeevsky aul, where an old Circassian woman named Fatimat lived. She took the patient to boarding school. I drank kefir. Gradually, the women became friends, and Fatimat entrusted the guest to cook kefir herself. In the meantime, the patient began to get better. Decreased cough. Breathing became free. The sputum came out more easily. Sigalova spent several months in the village. At parting, Fatimat gave her ward several hundred kefir "grains".
Having believed in the healing power of kefir, the recovered woman began to send the leaven to doctors in different cities. Medicine has confirmed the beneficial effect of kefir on the human body. A drink from the Caucasus soon came to exhibitions in St. Petersburg, Warsaw. It was shown in Paris and Chicago. At first, the price of kefir "grains" was high. They paid ten rubles for a spoon. But after some time they began to sell bags, at a ruble per pound.
How kefir "grains" originated is still unclear. They think that they were found in an insufficiently scraped waterskin, where milk was poured for fermentation. They look like lumps rice porridge. This is a symbiosis - the peaceful coexistence of a lactic acid microbe and a yeast fungus. The microbe ferments the milk, turning it into curdled milk. yeast fermenting milk sugar. Carbon dioxide is released. It loosens the milk clot of curdled milk. It becomes uniform.
There is another type of symbiosis, where yeast fungi participate - "kombucha". In alliance with a yeast fungus, there is not a lactic acid microbe, but an acetic acid bacterium. Together they form a jellyfish-like creature that swims in the sweet tea solution. Sugar is fermented to alcohol. Alcohol - to acetic acid. Tea provides nitrogen nutrition to the fungus.
The pleasant, sour drink was spreading wider and wider, when suddenly a hail of accusations rained down. Serious concerns have been raised about the carcinogenicity of tea kvass. It was said to cause stomach cancer. Connoisseur kombucha Professor B. Barabanchik conducted a special study. It turned out that the patients confused the cause with the effect. Facts were judged. A person began to drink tea "kvass", and subsequently he was diagnosed with cancer.
In fact, a person begins to drink tea “kvass” because he already has cancer. And at the same time, the acidity of gastric juice is lowered almost to zero. And a person wants more and more sour. Here "he drinks sour and nice drink born by fungus and bacteria.
But, of course, the most important yeast is not kefir or tea, but baker's. From a human point of view, of course. Annually they require 700 thousand tons. Humanity has been using their lifting power for so long that they have already lost their wild relatives. Only cultural yeast remained. These are now shaking. Trying to create ideal conditions. Not only do they fertilize them with all kinds of salts (plants after all!), But they also add juices. Cucumber, watermelon and even pumpkin. In addition, carrots, potatoes and ... peas! Juices are especially needed when growing yeast from spores. In infancy, every organism requires special care and attention. Yeast is no exception. Then, when they grow, they need a lot of air. It is blown through from below, and then the yeast mass in the vats is agitated, like boiling borscht in a camp soldier's kitchen.
Brewer's yeast is a special article. They are useful not only because they give beer, but even more because they contain vitamins of group B. For weakened people and those who have caught a cold, brewer's yeast is prescribed first of all. The medicine is harmless, trouble-free, only requires skillful handling. Anyone who goes to the brewery for the first time does not know what trials await him on the way back. He is poured a jar of yeast at the factory. They ask: "Full or half?" “Full,” nods the cold. Request completed. With a precious burden, the poor fellow hurries home. If the matter takes place in the summer, then he soon finds that the yeast overflows. It's warm, and they have developed a vigorous activity. Carbon dioxide foams the liquid mass. And she stubbornly climbs out of the can.
Finally, the owner of the medicine catches himself thinking that it is possible to cool the treasure, and sticks the jar under the stream of water in the street column. This calms down the dispersed fungal cells. The foamy mass shrinks, decreases in volume. Now the victim is anxiously watching how much medicine will remain in the jar. Is it possible to go to the factory again?
In recent years, opinions about yeast have been divided. Some are for, others are against. Those in favor have tested the power of yeast on mice. The mice were divided into two groups. One received normal food, the other added yeast. The first ones went their way in life, meeting the usual deadlines. The second survived them almost twice. They also gave birth. So, it seems that yeast is the companion of centenarians?
Let's hear the other side now. They make no less compelling arguments. Of course, yeast treats nerves and colds. But the proteins in yeast are very unusual. Not the same as in milk and meat. Especially amino acids. In addition, there are also toxic fatty acids. Many poorly studied biologically active substances.
Biotechnology is a newfangled word, but people learned to use microorganisms for their economic needs thousands of years ago. This, of course, is about yeast, without which neither winemaking, nor brewing, nor baking would be possible. So what is yeast? How were they "domesticated"? How are produced industrial way? And is it true that yeast bread is dangerous? Let's try to figure it out.
Yeast is available in three types: traditional pressed (pictured), liquid suspension (yeast milk) and dried. From the point of view of consumer properties, there is practically no difference between them, but Russian bakeries prefer liquid and pressed yeast, while dried ones are more convenient in everyday life.
Take an unwashed plum or grape in your hand. See white coating? Many microscopic sweet tooth are on the surface of the berries. In a certain phase of life, they are able to cause fermentation: eat sugar and release alcohol and carbon dioxide. Although we buy specially produced yeast for the needs of bakery, generally speaking, these microorganisms are by no means a rare species - they exist in abundance around us.
Unrecognized life
If they were not so common, the fateful meeting of man with yeast might not have happened, and who knows how this would have affected the development of human civilization. And so, due to the fact that yeast lives on cereal crops, and on hop cones, beer has become one of the oldest food products- it was cooked, apparently, 10,000 years ago. Later, in the II millennium BC. appeared yeast dough. Both products of yeast metabolism came in very handy for mankind: alcohol became one of the oldest and most popular drugs in the world, and carbon dioxide saturated beer with bubbles and perfectly loosened the dough, giving it splendor and increasing it in volume.
As probably many people know, yeast is mushrooms, but mushrooms are unusual. Unlike fly agaric and russula, they do not form a specific vegetative body - mycelium - and exist in a single-celled form. In total, there are about 1500 types of yeast, and they belong to two large groups - ascomycetes and basidiomycetes.
The yeast cell propagation process consists of several laboratory and industrial steps. From a 10 ml tube containing a small population of yeast cells surrounded by a sterile environment, several tens of tons of yeast are obtained as a result.
Using yeast for thousands of years, until relatively recent times, by historical standards, people did not even suspect what they were actually dealing with. Yeast was able to see through a microscope Anthony van Leeuwenhoek in 1680, but did not understand that he was living organisms. Only Louis Pasteur in 1857 managed to prove the connection between alcoholic fermentation and the vital activity of microscopic fungi.
All this, however, did not prevent the improvement of yeast cultures for thousands of years by preserving successful starter cultures. Spontaneous selection was replaced by directed selection (just after Pasteur's discovery), and today laboratories of scientific institutes and food companies are working on improving yeast strains.
Mushrooms in a jar
If only a few enthusiasts are engaged in winemaking and brewing at home, then bread-making using yeast happens from time to time in almost every home, which is why baker's yeast is the most important for all of us. interesting product. PM talked to Vitaly Vysotsky, director of the Voronezh yeast plant, part of the Lesaffre group, about how baker's yeast is developed and produced, as well as about some of the myths associated with it.
“The selection and research of yeast strains is carried out by a special scientific division of the Lesaffre group,” says Vitaly Vysotsky. - Some cultures can work well, for example, with sweet dough, others - with other types of test. Yeast cell strains reproduce in pure form. This is the know-how of the company, and their samples are stored at low temperatures in a special storage bank in the city of Marc-en-Barolles. It is from this storage that the group's enterprises receive test tubes containing a chilled sterile (that is, purified from other microorganisms) medium and only a few grams of yeast cells of an accurately identified type. Yeast production consists in the fact that, through several stages of reproduction, a small population of yeast cells from a test tube gives rise to yeast in commercial quantities (hundreds of tons).”
Forced to breed
A mushroom population undergoes several stages of reproduction. The first two are carried out under sterile laboratory conditions. First, 500 ml is obtained from 10 ml. Then from 500 ml - 10 liters of medium containing yeast cells.
These 10 liters already reach the production site. First stage consists in the production of a pure culture - the so-called mother yeast, the collection of which is already several hundred kilograms. Further, during the first generation and commercial generation, the yeast mass increases to several tens of tons.
Interestingly, the process of yeast production is in a kind of antiphase with respect to their practical application. “Yeast has both aerobic and anaerobic modes of life,” explains Vitaly Vysotsky. - In the absence of oxygen (as, for example, in a dough or liquid), the body of a yeast cell is aimed at survival, and not at reproduction. It is in this phase that the cell secretes a large number of alcohol and carbon dioxide, so the anaerobic way is really good for us. However, in the production of yeast, it is necessary that the cells actively multiply, and for this they need not only nutrients, but also oxygen.”
Yeasts, in particular fungi from the Saccharomyces family, which are used in baking, reproduce vegetatively by budding. First, an outgrowth appears on the mother cell, then mitotic division of the nucleus occurs, the formation of a cell wall and separation of cells from each other. The mother cell is scarred by budding, which makes it possible to determine its age. Usually, the mother cell can form 20-30 buds.
The production process is the creation and control favorable conditions for yeast propagation. These conditions are the presence of sufficient nutrition and access to oxygen. The main food sources for yeast are easily digestible sugars, i.e. glucose, maltose, sucrose, galactose. Mineral substances and vitamins are also needed so that the cell has everything necessary for the construction of the kidney.
Therefore, for the production of yeast, it is necessary to prepare a nutrient medium, place the yeast in it, and, as the yeast absorbs substances from growth medium, add food and purge all this mass with air oxygen. When the mass fills the entire container, the process must be stopped and separation should be carried out - to separate the yeast cells from the medium. After that, only the process of forming the final product remains.
The traditional end product in Russia, and indeed in the world, is pressed yeast. As a rule, these are briquettes consisting of yeast cells, purified from the medium where they grew, and passed through special washing and filtration in vacuum filters. The briquetted yeast contains 32% yeast cells and 68% water.
Yeast is available in three types: traditional pressed (pictured), liquid suspension (yeast milk) and dried. From the point of view of consumer properties, there is practically no difference between them, but Russian bakeries prefer liquid and pressed yeast, while dried ones are more convenient in everyday life.
In the production of dried granular yeast, the propagation technology is similar, however, other strains are used - those that are more resistant to the final stage of production - drying. Drying (dehydration) is an extreme effect on the cell, and not all cultures are able to withstand it. The product goes through the stage of compressed yeast, which is then extruded through the extruder in thin "noodles". After that, they are finely chopped and sent to the dryer. There with the help of supercharged warm air yeast is dehydrated. This completes the process, the product is ready for packaging.
Yeastless mythology
The specificity of the modern information field is such that so-called horror stories are often used as a tool to attract the attention of the public. The calculation is made on the fact that fear is exactly the emotion that will make a person highlight this or that news in an endless and saturated information flow. Revelations about the dangers of certain foods are especially popular. People are scared by genetically modified vegetables and fruits, preservatives and flavorings. This series also includes ordinary baker's yeast, which allegedly damages the intestinal microflora, getting inside our body along with bakery products.
One of the myths is related to the so-called thermophilic yeast, which, they say, can survive the temperature of baking and then enter our digestive system alive. As an alternative, various types yeast-free starter cultures. As usual, the source of this kind of "hypothesis" is not biologists and production workers, but some enthusiasts " healthy eating» different professions.
Lesaffre group experts consider all these arguments unprofessional and ridiculous. First, no thermophilic yeast that can survive baking does not exist in nature. By the end of baking in the center of the crumb bakery product the temperature reaches + 96−98 ° С. At a temperature of +50°, inhibition of the vital activity of yeast cells begins, and at +55°, the protein in them is denatured and the yeast cells die.
Secondly, it is impossible to avoid getting live yeast into the body. As already mentioned, yeast is not only sold in stores, but also lives around us. Microscopic mushrooms will definitely be eaten by us along with fruits and other plant food. There is, for example, a “folk” alternative to store-bought yeast in the form of plain water infused with raisins. In fact, this alternative is imaginary, since purchased yeast is replaced by the same yeast, only of other species that inhabit the surface of dried grapes. By the way, if you simply combine flour with water, replace the dough and put it in heat, after a while yeast fermentation will still begin there, because flour contains many microorganisms, including yeast cells. Another thing is that cultural strains that have undergone directed selection will give a predictable result, but other types of yeast taken from the environment, especially in combination with other microorganisms, can give the dough undesirable taste and organoleptic qualities.
Thirdly, if we do not talk about purely chemical dough leavening agents, then the proposed biological yeast-free starter cultures are not 100% such. Indeed, in baking, for example, in the manufacture of rye bread, have long been used starter cultures based on lactic acid bacteria. But in reality, they are a symbiosis of bacteria and the same yeast cells. lactic acid bacteria by themselves cannot provide sufficient gas formation to quickly saturate the dough with carbon dioxide.
Dry or wet?
The last question we asked the director of the Voronezh Yeast Plant was probably asked by all home bakers more than once. What is the difference between pressed (wet) yeast and dried yeast, which are produced not in briquettes, but in small granules?
“From the point of view of consumer properties, there is no difference, and we produce yeast in all forms,” says Vitaly Vysotsky. But there is a technological difference. For old bakeries, pressed yeast is preferable, since it is under them that the technology of their work is built. The main disadvantage of pressed yeast is the need to store it at a low temperature - in the range from 0 to +4°C. At higher temperatures, the cells enter the active phase, vital processes begin, which leads to a further increase in the temperature of the briquette. Dried yeast has a longer shelf life, and they do not need to create conditions - they are perfectly stored at room temperature. In addition, they are usually packaged in small packages, which is much more convenient in everyday life.
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