At what temperature does brewer's yeast die? Alcoholic fermentation - the magic of turning sugar into ethyl alcohol

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Microorganisms are usually divided into three categories depending on their behavior under conditions of different temperatures, which reflects the adaptability or resistance of their enzymatic apparatus to this factor. Microorganisms are called psychrophilic, mesophilic or thermophilic, the optimal development of which occurs at temperatures below 20° C, between 20 and 45 and above 45° C, respectively. Yeast falls into the first two categories.
Temperature is important factor vital activity of all yeasts; For each of the different functions of yeast cells: respiration, fermentation, growth, there are optimal, minimum and maximum temperature conditions. In fact, these limits depend on the type of yeast and even on the race, as well as on aeration, the composition of the medium, especially the presence of alcohol, and thus determine a more or less wide zone in which the growth of yeast and the fermentation of sugar is possible.
The effect of temperature on yeast has been the subject of many studies, and precise data can be found on this subject (Uhl, 1960, 1967; Rose, 1962; Stocke, 1971). The question of the importance of temperatures in winemaking was developed by Dimotaki-Kuraku (1966).
Ug (1964, 1966) conducted an experiment to study the influence of temperatures from 10 to 33 ° C on the rate of fermentation of grape must in correlation with other factors: pH, sugar content, alcohol content, ammonium hydroxide hydrate content; The retarding effect of low pH and the presence of alcohol is enhanced by high temperature. Martini (1964) studied the yeast Sacch. pastorianus and, first of all, the duration of fermentation.
Effect of temperature on yeast metabolism
The intensity of respiration (Qc) and fermentation (QcojO) of wine yeast at various temperatures, for example from 15 to 45 ° C, can be measured using a Warburg apparatus (see Fig. 5.7). It must be recalled that this apparatus, which acts as a micromanometer, records the release of carbon dioxide (fermentation) or the absorption of oxygen (respiration) by yeast of a given mass over a short time.In this way, the instantaneous rate of these phenomena is measured (Table 7.6).It is also possible to monitor the release of gas by weighing over a longer period (Table 7.7) .

Table 7.6
Average values ​​of respiration and fermentation rates of various Saccharomyces species depending on temperature, mm 3 gas per 1 g of dry yeast per hour

Table 7.7
Fermentation speed for different yeasts depending on temperature(according to Cantarelli, 1966), g CO, per 24 hours

Effect of temperature on the formation of secondary products

The intensity of yeast respiration increases with increasing temperature to 30°C, with every 10°C the values ​​approximately double; at temperatures above 30° C, breathing decreases. As for the intensity of fermentation, its optimum temperature corresponds to a temperature of about 35 ° C, i.e., slightly higher than for the optimum respiration; up to this temperature, the level of fermentation intensity also doubles every 10 ° C; at 40°C it decreases by 15%.
It is not difficult to notice the significant influence of temperature on the metabolism of yeast, which can be expressed by the following approximate rule: “fermentation of sugar at 30 ° C occurs 2 times faster than at 20 ° C,” or “for each additional degree of temperature, yeast converts in the same time 10% more sugar."
The optimal fermentation temperature for sugar varies depending on the type of yeast, as was shown in Chapter. 5. In table. 7.7 it ranges from 30 to 39° C.
Temperature affects not only the kinetics and limit of fermentation, but also the formation of products resulting from fermentation (Lafon, 1955). During fermentation at elevated temperatures, the alcohol yield is usually lower; on the other hand, more secondary products of Neuberg's glyceropyruvic fermentation are formed (glycerol, acetoin, 2, 3-butylene glycol, acetic acid). The exception is succinic acid(Table 7.8). Pyrogratic and α-ketoglutaric acids accumulate more at high temperatures (Lafon-Lafourcade and Peynaud, 1966). Higher alcohols are by far the products that change most with temperature. Their maximum formation occurs at 20° C. It decreases as the temperature rises. At 35°C this formation is no more than 1/4 of that observed at 20°C (Paynaud and Gimberto, 1962). This is probably one of the reasons why wines produced at high temperatures have less pronounced aroma.

The influence of temperature on the rate and limit of fermentation of grape must

As a rule, the higher the temperature (between 15 and 35°C), the shorter the latent phase, the faster fermentation begins. For example, to completely ferment grape must containing 200 g/l of sugar at 10°C, it will take many weeks, at 20°C -15 days, at 30°C - from 3 to 4 days. But on the other hand, the higher the temperature, the more limited the fermentation and the more unfermented sugar remains. In table 7.9 shows the results of observations made for this purpose on very sugary must of the Sauternes variety.

Fermentation speed and fermentation limit depending on temperature

Everything happens as if the yeast gets tired, exhausted, the faster the higher its activity at elevated temperatures. Even between 30 and 35° C, temperature is the limiting factor for fermentation. The lower the temperature, the higher the number of yeast cells at the end of fermentation. At high temperatures, reproduction occurs faster, but stops earlier than usual.
This law was formulated many years ago by Müller-Thurgau; it was later confirmed by many experimenters, including Castelli (1941). In table Figure 7.10 shows the results of a fundamental experiment conducted by Müller-Thurgau. The same wort was fermented, but with different sugar contents (127, 217 and 303 g) and at different temperatures; the experiment showed both a delay caused by increased sugar content and the influence of temperature.
The limiting effect of temperature sometimes manifests itself even at alcohol content less than 10 or 11% vol., at relatively low levels, for example, below 27 ° C and, in any case, significantly below 36 ° C, i.e., a temperature that is often considered critical limit. These results have great importance, as they show how difficult it is to set an exact limit on fermentation temperature.

Alcohol content in % vol. depending on fermentation temperature(according to Müller-Thurgau)

In Fig. Figure 7.8 shows the curve of fermentation limits for various types of yeast depending on temperature. Most Saccharomyces species have an optimum at about 20°C. Non-sporogenous yeasts, in particular Brettanomyces, ferment sugar better at a temperature of about 26°C.

Rice. 7.9. Progress of fermentation of grape must with measurement of the amount of CO2 released from Sacch. baillii at temperatures (optimal 25° C) (in "C):
Graphs in Fig. Figures 7.9 and 7.10 show the evolution of fermentation for two Saccharomyces species with different sensitivities to temperature conditions. The lower the temperature of the wort, the more the fermentation curve becomes straight; at 4°C the evolution becomes almost linear, and, conversely, the higher the temperature, the larger the initial angle, the more and faster the curve tends to an asymptote. At low temperatures, it is actually the limiting factor; inhibitory effect of alcohol and exhaustion nutrients play a lesser role. On the other hand, the higher the temperature, the more alcohol, as it forms, inhibits the growth of yeast.
/ - 4; 2 - 13; 3 - 20; 4 - 25; 5 - 30; 5 - 35.

Rice. 7.10. Progress of fermentation of grape must with measurement of the amount of CO*C released
Sacch. uvarum at temperatures (optimal 13°C) (in °C):
Another important note regarding the effect of temperature on growth

Rice. 7.8. Fermentation limits measured by CO2 released for various types of yeast depending on temperature:
;-4; 2 - 20; 3 - 25; 4-13; 5 - 30; 5 - 35.
1- Kloeckera; 2- Torulopsis; 3 - Brettano myces; 4 - Saccharomycodes; 5 - Saccharomyces.

yeast: aeration, which can be practiced and recommended at the beginning of fermentation, produces a different effect depending on the temperature of the environment. The greatest acceleration is obtained at 25 ° C. At higher temperatures, the yeast does not use all the dissolved oxygen. On the other hand, aeration in the cold is ineffective; for example, aeration by overflowing at 20°C is less beneficial than at 25°C.

Temperature changes during fermentation

In Fig. Figure 7.11 shows how the fermentation proceeded. Below are some conclusions from the observations, but without the intention of providing a complete summary.
1. Heating can have the opposite effect depending on the degree and intensity of aeration. It is possible that the optimum temperature for yeast in aerobiosis and anaerobiosis is different.

Rice. 7.11. .

1. Cooling, for example, from 30 to 25 ° C accelerates fermentation with access to air and delays it in the absence of air. Lowering the temperature towards the end of fermentation, at a point when the yeast can no longer reproduce, can ultimately have the opposite effect of what is intended.
2. Under conditions without air access, the higher the initial temperature, up to 25 ° C, the faster and more complete the fermentation occurs when it is subsequently lowered to 20. This fact was already observed by Müller-Thurgau (1884). Consequently, the increased temperature initially promotes fermentation .
3. In the presence of air in a bottle covered with cotton wool, exactly the opposite phenomenon is observed, and the rate of fermentation at a given temperature was as much greater as the temperature during fermentation was lower.

This was pointed out by Saller (1953).

1. The temperature at which yeast begins to develop is decisive for the entire subsequent fermentation process. The best fermentation is achieved at a temperature that remains constant from start to finish, hence it is advantageous to use a constant temperature fermentation system.

It may seem counterintuitive that yeast can withstand a temperature of 35° C better from start to finish than a gradual increase from 25 to 35° C. To achieve good fermentation at elevated temperatures, it would generally be better to start and carry it out at this temperature. Thus, spontaneous fermentation of heated grapes was observed at temperatures much higher than those maintained under normal conditions.
It can be assumed that the enzymatic activity of yeast depends on temperature and adaptation to the initial temperature of fermentation takes place. Sensitivity to temperature variations during fermentation may be a specific property acquired by the first generations of yeast.

Even distillers with sufficient experience in making strong alcohol cannot always say how much is fermenting and what influences it. It is still impossible to determine this with an accuracy of one day, since The fermentation process depends on many factors:

• raw materials used for wort;
• maintaining proportions when adding ingredients;
• room temperature and humidity;
• compliance with brewing technology;
• Not the least of the reasons is water. Eg, boiled, deprived of oxygen, slows down this process.

In order to determine the fermentation time with the greatest probability (if all the above influence factors are correctly observed), first of all need to rely on the raw materials used.

1. The most popular - if the manufacturing technology is followed, the wort becomes ready for distillation in a time from 5 to 14 days. It is after five days that you need to look at it and check for readiness. Although, as a rule, the most optimal period is 7 – 10 days.
2. The mash, the basis for which is starch (its sources are grain, potatoes, ready-made starch), ferments much less - already from 3 – 5 days she is ready to be driven.
3. For fruit and grape mashes using yeast, it is required about two or even three weeks for maturation.
4. If yeast is not added specifically, but only wild yeast found on fruits (berries) is used, then fermentation may take longer up to 45 days. It's very It is important to use a water seal oh, otherwise the food may turn sour and you will end up with vinegar, which is also not bad, but our goal is completely different!

Peculiarities. The indicated time is relative, since much also depends on the temperature.

The process works best if the room temperature is between 20 – 22°C. It is acceptable from 18 to 28°C, but it is not advisable to go beyond these limits.

How long can you steep the mash?

A situation is possible when fermentation is already completed, and you do not have the opportunity in the coming days.

First of all, make sure that you have a truly finished product.

Fully ripened mash has strong alcohol smell, there is no release of carbon dioxide (no bubbles or hissing).

This can be checked with a lit match: if you bring it to the surface of the mash and it continues to burn, it means that carbon dioxide is not released and there is no fermentation.

And most importantly - the mash tastes bitter, without the slightest sweetness.

In order not to lose a valuable product, and fermented and acidified mash will produce moonshine with an unpleasant odor and taste, you need to take the container to the basement or just a cold room with a temperature of 10 to 0°C. This will prevent souring of the mash and besides, it takes 5 – 7 days. All that remains is to drain the sediment and distill. Most types of ready-made mash can be infused in “basement” conditions for up to a month or even more without loss of quality.

Attention! You cannot steep grain mash for a long time, even in the cold.

Acid inevitably accumulates in it (acetic acid fermentation begins) and as a result, instead of moonshine with a pleasant grainy taste, you get sour booze.

How to stop fermentation of mash?

It is possible that you will someday need to stop fermentation, because moonshine is needed urgently, and you see that the process is still ongoing. Can artificially stimulate its cessation.

Please note: if fermentation is not complete, during distillation you will get less strong moonshine than expected, since the yeast has not had time to process the sugar into alcohol.

The most suitable additive for stopping fermentation is leftover from previous distillations “tails” with a strength of about 25°. They will add alcohol to the wort and the yeast will die. In addition, this way you use the “waste” product to your advantage and will not lose in the amount of alcohol produced.

How to speed up fermentation?

But knowing in advance that you need fast-ripening sugar mash, resort to one of the suggested tricks (or even several at once).

So that if possible accelerate ripening, use these methods:

• using only the freshest yeast. Under suitable conditions, they will act more actively and quickly complete their task of converting sugar into alcohol;
• adding bread crusts to the wort accelerates ripening. You probably observed this yourself during cooking;
• pre-diluted and added tomato paste: up to 100 g per 10 liters of wort;
• peas or corn in the amount of 300 - 400 g per 10 l;

Please note. Peas, added after the fermentation process has begun, can produce a lot of foam, which is quite easily extinguished by the crumbled biscuits.

• increasing the amount of water or decreasing the amount of sugar compared to what is specified in the recipe (no more than 20%) also speeds up ripening. But be prepared for the fact that you will get less strong alcohol during distillation;
• adding unwashed raisins will speed up the process due to wild yeast on its surface;
• stirring the wort daily (several times possible). When stirring, gas bubbles are intensely released, which also speeds up ripening.

A few questions about fermenting mash

Many (especially beginners) moonshiners have accumulated questions, which we will try to answer below.

Braga has not fermented, is it possible to drive it away?

Of course, it is not advisable to do this, but in case of emergency, it is possible. Take advantage tips for stopping fermentation. But a shortage of alcohol is almost certainly guaranteed. Incomplete fermentation means that the sugar has not yet been converted into alcohol.

Carefully. During distillation, foam may be released, which will affect the quality of the product. In this case, secondary distillation helps.

Why does mash ferment for a long time?

As already noted, there are many factors that influence the duration of ripening. In addition to the quality of the ingredients, it is imperative pay attention to the room temperature. If it is below 18°C, then the vital activity of the yeast is very weak, so the process is sluggish. Above 30°C, their vital energy also decreases, and at around 40°C they die completely.

In addition, the fermentation tank should not be placed on a cold floor (tile, porcelain tile, stone). There should be a warm base underneath. Otherwise, even if the room is 22°C, the mash may be 16 degrees, which is unacceptable.

What to do if the mash runs away?

Most common reasons increased foaming:

• using baker's yeast instead of alcoholic yeast or accidentally exceeding its quantity;
• adding honey to the wort instead of sugar;
• malt and grain raw materials at the first stage of fermentation can also produce too much foam;
• exceeding the permissible volume for wort.

note: should be filled with mash to a maximum of 2/3 of the volume. And when using products that can potentially produce a lot of foam - only half.

Exceeding it risks the fact that you will have to collect the wort on the floor, wash the containers, and in this case you will also lose some of the alcohol.

But it happens to many people that the wort foams, and something urgently needs to be done about it. Therefore, we offer several options:

• The best way if foam suddenly appears is move the container to a colder room for a couple of days, and then return to comfortable conditions for mash. But do not overdo it, it is advisable that the temperature is not lower than 15°C.
• There is no such possibility then divide the wort into two containers. After a couple of days, when the violent foaming stops, drain together again.
• Crumble over the wort 1-2 cookies.
• Pour into container vegetable oil , which also extinguishes foam quite well. A couple of tablespoons is enough.
• Add some ice. This will help reduce the amount of foam, but will slow down the fermentation.

Braga has stopped fermenting, but is still sweet

Here are the main reasons:

• Not enough yeast. This is easy to fix: add and the process will resume.
• Too much sugar (the proportion is wrong: for 1 kg - 4 liters of water). Solved by adding water and yeast.
• The room is cold (hot). Bring the temperature to optimal levels for yeast activity (22 – 28°C).

Also consider possible reasons already listed above in this article.

Is it possible to put mash in an aluminum flask?

Many generations of moonshiners have used aluminum milk flasks for mash. However, research in this area does not confirm the safety of the material. According to the recommendations of scientists and doctors, even aluminum pans are not recommended for storing acidic foods: cabbage soup, borscht, solyanka.

Temperature is one of the main factors in proper moonshine brewing. Chemical reactions occurring in the mash will be slowed down or will not begin at all if you do not prepare for them optimal conditions. What temperatures are we talking about and how to maintain them correctly?

Note that rarely any reaction requires a strictly defined temperature. Typically, a spread of several degrees is assumed, for example, from 18 to 28, at which the chemical reaction proceeds qualitatively. Not everyone has laboratories at home with a bunch of thermometers, so average values ​​are taken as a basis, which can be easily maintained at home.

To measure the temperature of the mash, use a thermometer with a probe

The generally accepted indicator is temperature from 20 to 30 degrees Celsius. When such conditions are maintained, yeast of almost all types will actively work. When using baker's, dry, alcohol, wine, beer or turbo yeast, this thermal environment will be optimal.

“Cooking” yeast is much easier than “freezing” it. So try to contain the heat rather than give it in.

• At a temperature below +5 degrees, any type of yeast will die. If you accidentally froze the mash, then you need to warm it up and add the fungi again.
• From +5 to +20 the yeast exhibits extremely low activity, but continues to live. They are in a kind of hibernation. When the temperature rises, they wake up, and when the temperature drops, they die.
• From +20 to +30 you will achieve maximum fermentation efficiency. This is an ideal to strive for.
• From +30 to +42 you risk ruining the mash. The point is that the temperature environment lower than in the fermentation tank. When the process is too active, a lot of heat is released and the fungi may not withstand such “heat”.
• When increasing more than +42 degrees, all the yeast that is used in the fermentation of the mash dies. It seems that achieving such boiling water is very difficult, but in practice it is a common occurrence.

It's safer to keep the temperature a little lower. No one can say 100% how the mash will behave in a given situation.

If it “plays” very actively, then due to the heat generated, the liquid can heat up and destroy all the beneficial fungi. It is very difficult to bring it to +5, but to +50 without problems.

At what fermentation temperature is more moonshine produced?

An interesting study was carried out by measuring the efficiency of fermentation and the release of harmful substances at different temperatures. It turned out that when 30 degrees Fermentation proceeds 4 times faster, and the amount of fusel oils formed is 4 times less. The alcohol emission in this case is 10% less.

At 20 degrees"exhaust" produces more alcohol, but the mash costs longer. More harmful substances are also produced. Double distillation with separation of fractions completely solves the issue of the quality of moonshine, so if quantity is more important than speed for you, then it is better to keep fermentation at the minimum permissible temperature.

The results of the study are presented in the photo below.

What devices can maintain the optimal temperature of the mash?

There are no specialized solutions yet, so we will use the ingenuity and experience of other moonshiners. Below we will describe the three most well-known methods that will help you preserve the contents of the fermentation tank under certain conditions.

Just don't laugh, it really works effectively. We set the required degrees, lower it to the bottom of the fermentation tank and monitor the temperature of the mash itself. It will be slightly higher due to active chemical reactions, so it is better to reduce the power by 2-3 degrees.

Price from 300 to 1500 rubles. You can order on AliExpress or buy at a pet store.

Aquarium water heater with thermostat

Heating pad for belt

The operating principle is as follows: we wrap the heating pad around the fermentation tank, set the required degrees and turn it on. In a cold room, it may not solve the whole problem, but its effect will be 100%.

The price is about 1000 rubles.

Heated mat

In this case, the fermentation tank is simply placed on a heated place and the heat comes from the floor. Considering that cold sinks and heat rises, heating the liquid from below is a very correct solution.

Price from 1000 to 1500 rubles.

In order to prepare the mash correctly and get the product at the end High Quality the need to meet a number of conditions. The key issue in the cooking process is the required temperature. How to choose it correctly, and what does this choice depend on?

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Fermentation mechanism

To begin with, it’s worth remembering what mash is and what role the fermentation process plays in its production. Braga is a whole closed ecosystem. It’s not just yeast, sugar and other components mixed together haphazardly that create necessary conditions for the development of organisms that provoke fermentation. Braga is a complete environment for the appearance of microorganisms such as fungi. Due to their reproduction in the structure of the mash, complex carbohydrates are converted into alcohol.

Such fermentation products obtain their energy in a simple “human” way - by processing oxygen obtained from the environment into carbon. But this process will occur correctly provided there is access to fresh air and sunlight. Then, due to the addition of more complex carbon compounds such as glucose or sucrose, the yeast structure changes its nutrition, producing energy from sugar. This provokes the release of carbon dioxide and, most importantly for us, ethyl alcohol into the drink.

The so-called “wild” yeast, which can cause this process to occur, is also available in its natural, original form. These include most fruits and leaves. Over the course of its existence, winemaking and the production of strong alcoholic beverages have managed to transform into something unlike the works of their ancestors, but the basic principles are still unchanged.

Creating ideal conditions for the right mash?

The process of preparing a truly high-quality base for any strong drink made from mash requires compliance with many nuances:

• The required amount of resulting mash. From this volume depends utensils used.
• Its material (most importantly - not aluminum).
• The percentage of sugar contained in the original volume of the mixture.
• Yeast used and its quantity.
• Presence of a water seal.
• The room temperature of the room where the mash will be stored.
• Compliance with the correct sequence of actions during manufacturing.

What temperature conditions are needed to make mash?

We won’t bore you with long introductions. The temperature required to obtain the output mash of the highest possible quality, provided that all other parameters are observed, is in the range from 20C to 28C. A decrease or increase in one direction or another is permissible by no more than 2C.

When crossing the lower temperature limit (18C is the limit), the yeast “dies”. This entails a total reduction in the quality level of the final product. If working temperature above the maximum permissible 30 degrees, this causes excessively rapid fermentation, and as a result, the mash will not work either. Very high temperatures cause the protein to coagulate and the inevitable death of the “yeast”. This is also due to the fact that during the fermentation process, the mash, due to the constant release of heat, sometimes heats up on its own. If the temperature is within the upper permissible limits, this is sometimes decisive.

What to do in case of violation of operating temperature ranges and influence?

When fermenting mash, the most important thing is to remember one simple thing. Keeping the temperature within the recommended temperature limits does not in any way affect the quality of the product. Those. there is a minimum limit of 18-20C and a maximum of 28-30C. Temperature fluctuations within these limits do not directly affect the quality of the mash. More than this range is not possible, less is also not possible. But there is no difference between 22C and 26C. The main thing is not to cross the boundaries of permissible temperature values.

If they decrease, an excellent way to eliminate this would be to purchase an aquarium-type water heater in advance. A special thermometer, which aquarists use in their work to most accurately determine the water temperature, will also be an invaluable assistant. If searching for this unit causes you inconvenience, you can also use a regular room “thermometer”.

If the temperature of the mash has exceeded the upper range of permissible temperature values, its forced reduction is required. In particular, this applies most strongly to those cases when large-volume dishes are used as a container for mash. This is directly related to the spontaneous increase in temperature of the mixture due to the activity of yeast. The most in a simple way“To bring down the temperature” will be the most ordinary ice cubes.

Is there any other way to influence the fermentation rate?

Fermentation can always be accelerated using available means, with a minimum of effort. Here, again, it is necessary to remember that all yeast are completely living microorganisms. Like everything else on our planet, they want to reproduce. But they do this only in conditions that are comfortable for themselves. And, in addition to the correct temperature regime, when creating them you need to be guided the following rules:

• The fresher the better. Old yeast greatly inhibits the fermentation process. Therefore, you should not skimp on the time it takes to find a high-quality, specialized product. Good yeast can then be used instead of sourdough.
• When adding, add. By adding a little more yeast than the required amount, you can also speed up the process. Or you can use the following method - pour in a little ammonia, based on the calculation of 10 drops per 1 liter. If you don’t like this kind of “chemistry” as an additive, then add some grains and mix them into the mash.

Conditions and terms of storage of the finished product and what to do if you do not have a specially designated room for this?

If you are preparing mash without setting a goal large production, then it is likely that you will have a question, where to put it when it is ready? After all, most of us hardly have a specially designated cellar or a separate room for this purpose, equipped with first-class refrigerators, thermometers, electronic devices, and so on. In such a situation, the first thing you need to do is decide how much time you need?

The main thing to remember is that the lower the ambient temperature in relation to the mash, the better. At average room temperatures - from 24 to 30 C - the shelf life of the drink is extremely short. Just a few hours. During this time, the drink loses its taste and acquires an unpleasant odor. Accordingly, you cannot leave a container with finished mash near the pipe and windows, through which the sun’s rays will additionally heat the mash.

If you need to store the drink for a longer period - the best option there will be a refrigerator or a cold basement in the house (if, of course, you live in a private house and you have one). In this case, subject to maintaining a temperature of 2 C to 5 C, the “life” of the mash increases to several weeks. As a rule, the maximum period during which a drink will not significantly change its taste characteristics is 21 days. But it is still recommended to consume it within the first 7 days in order to enjoy its excellent taste to the maximum.

In conclusion, I would like to say that preparing mash in compliance with all recommendations and creating all the required conditions guarantees you a high-quality drink. You will always know how and what it is made of. And awareness of your work will also help you enjoy its amazing taste. Taking the first sip of freshly brewed mash, you will feel an incomparable taste, flavored with a pinch of pride for yourself.

Alcoholic fermentation is the basis for the preparation of any alcoholic drink. This is the simplest and affordable way get ethanol. The second method, ethylene hydration, is synthetic and is rarely used and only in the production of vodka. We'll look at the specifics and conditions of fermentation to better understand how sugar turns into alcohol. From a practical point of view, this knowledge will help create an optimal environment for yeast - correctly placing mash, wine or beer.

Alcoholic fermentation is the process of yeast converting glucose into ethyl alcohol and carbon dioxide in an anaerobic (oxygen-free) environment. The equation is as follows:

C6H12O6 → 2C2H5OH + 2CO2.

As a result, one molecule of glucose is converted into 2 molecules of ethyl alcohol and 2 molecules of carbon dioxide. In this case, energy is released, which leads to a slight increase in the temperature of the environment. Also, during the fermentation process, fusel oils are formed: butyl, amyl, isoamyl, isobutyl and other alcohols, which are by-products of amino acid metabolism. In many ways, fusel oils form the aroma and taste of the drink, but most of them are harmful to the human body, so manufacturers try to remove harmful fusel oils from alcohol, but leave the beneficial ones.

Yeast are unicellular spherical fungi (about 1,500 species), actively developing in a liquid or semi-liquid medium rich in sugars: on the surface of fruits and leaves, in the nectar of flowers, dead phytomass and even soil.

These are one of the very first organisms “tamed” by humans; yeast is mainly used for baking bread and making alcoholic beverages. Archaeologists have established that the ancient Egyptians 6000 BC. e. learned to make beer, and by 1200 BC. e. mastered baking yeast bread.

Scientific research into the nature of fermentation began in the 19th century; J. Gay-Lussac and A. Lavoisier were the first to propose the chemical formula, but the essence of the process remained unclear, and two theories arose. The German scientist Justus von Liebig assumed that fermentation is of a mechanical nature - vibrations of the molecules of living organisms are transmitted to sugar, which is broken down into alcohol and carbon dioxide. In turn, Louis Pasteur believed that the fermentation process is based on biological nature - when certain conditions are reached, yeast begins to convert sugar into alcohol. Pasteur managed to prove his hypothesis experimentally; later other scientists confirmed the biological nature of fermentation.

The Russian word “yeast” comes from the Old Church Slavonic verb “drozgati”, which means “to press” or “to knead”, and there is a clear connection with bread baking. In turn, the English name for yeast “yeast” comes from the Old English words “gist” and “gyst”, which mean “foam”, “to produce gas” and “to boil”, which is closer to distillation.

The raw materials for alcohol are sugar, sugar-containing products (mainly fruits and berries), as well as starch-containing raw materials: grain and potatoes. The problem is that yeast cannot ferment starch, so you first need to break it down into simple sugars, this is done by the enzyme amylase. Amylase is found in malt, a sprouted grain, and is activated at high temperatures (usually 60-72 °C), and the process of converting starch to simple sugars is called “saccharification.” Saccharification with malt (“hot”) can be replaced by the addition of synthetic enzymes, in which there is no need to heat the wort, which is why the method is called “cold” saccharification.

Fermentation conditions

The development of yeast and the course of fermentation are influenced by the following factors: sugar concentration, temperature and light, acidity of the environment and the presence of trace elements, alcohol content, oxygen access.

1. Sugar concentration. For most yeast races, the optimal sugar content of the wort is 10-15%. At concentrations above 20%, fermentation weakens, and at 30-35% it is almost guaranteed to stop, since sugar becomes a preservative that prevents the yeast from working.

Interestingly, when the sugar content of the medium is below 10%, fermentation also proceeds weakly, but before sweetening the wort, you need to remember the maximum concentration of alcohol (4th point) obtained during fermentation.

2. Temperature and light. For most yeast strains, the optimal fermentation temperature is 20-26 °C (bottom-fermenting brewer's yeast requires 5-10 °C). The permissible range is 18-30 °C. With more low temperatures Fermentation slows down significantly, and at values ​​​​below zero, the process stops and the yeast “falls asleep” - falls into suspended animation. To restart fermentation, it is enough to raise the temperature.

Too much heat destroys yeast. The stamina threshold depends on the strain. In general, values ​​above 30-32 °C are considered dangerous (especially for wine and beer), however, there are certain races of alcohol yeast that can withstand wort temperatures up to 60 °C. If the yeast is “cooked”, you will have to add a new batch to the wort to resume fermentation.

The fermentation process itself causes an increase in temperature by several degrees - the larger the volume of wort and the more active the yeast is, the stronger the heating. In practice, temperature correction is done if the volume is more than 20 liters - it is enough to keep the temperature below 3-4 degrees from the upper limit.

The container is left in a dark place or covered with a thick cloth. The absence of direct sunlight allows you to avoid overheating and has a positive effect on the work of yeast - fungi do not like sunlight.

3. Acidity of the environment and the presence of trace elements. An acidic environment of 4.0-4.5 pH promotes alcoholic fermentation and suppresses the development of third-party microorganisms. In an alkaline environment, glycerol and acetic acid are released. In neutral wort, fermentation proceeds normally, but pathogenic bacteria actively develop. The acidity of the wort is adjusted before adding yeast. Often, amateur distillers increase the acidity with citric acid or any sour juice, and to reduce it, they quench the wort with chalk or dilute it with water.

In addition to sugar and water, yeast requires other substances - primarily nitrogen, phosphorus and vitamins. Yeast uses these microelements for the synthesis of amino acids that make up their protein, as well as for reproduction initial stage fermentation. The problem is that at home it is impossible to accurately determine the concentration of substances, and excess acceptable values may negatively affect the taste of the drink (especially wine). Therefore, it is assumed that starchy and fruit raw materials initially contain the required amount of vitamins, nitrogen and phosphorus. Usually only pure sugar mash is fed.

4. Alcohol content. On the one hand, ethyl alcohol is a waste product of yeast, on the other hand, it is a strong toxin for yeast fungi. When the alcohol concentration in the wort is 3-4%, fermentation slows down, ethanol begins to inhibit the development of yeast, at 7-8% the yeast no longer reproduces, and at 10-14% it stops processing sugar - fermentation stops. Only certain strains of cultured yeast, bred in laboratory conditions, are tolerant of alcohol concentrations above 14% (some continue to ferment even at 18% or higher). From 1% sugar in the wort, about 0.6% alcohol is obtained. This means that to obtain 12% alcohol, a solution containing 20% ​​sugar is required (20 × 0.6 = 12).

5. Access to oxygen. In an anaerobic environment (no oxygen), yeast is focused on survival rather than reproduction. It is in this state that maximum alcohol is released, so in most cases it is necessary to protect the wort from air access and at the same time organize the removal of carbon dioxide from the container in order to avoid high blood pressure. This problem is solved by installing a water seal.

With constant contact of the wort with air, there is a danger of souring. At the very beginning, when fermentation is active, the released carbon dioxide pushes air away from the surface of the wort. But at the end, when fermentation weakens and less and less carbon dioxide appears, air enters an unclosed container with wort. Under the influence of oxygen, acetic acid bacteria are activated, which begin to process ethyl alcohol into acetic acid and water, which leads to spoilage of wine, a decrease in the yield of moonshine and the appearance of a sour taste in drinks. This is why it is so important to close the container with a water seal.

However, to multiply yeast (achieve its optimal quantity) oxygen is required. Usually, the concentration found in the water is sufficient, but for accelerated propagation, after adding the yeast, the mash is left open for several hours (with access to air) and stirred several times.