2024 Author: Jasmine Walkman | [email protected]. Last modified: 2023-12-16 08:29
Quality yeast dough or the need to prepare fermented beverages is a science. Let's get acquainted with the details of what affects the quality of yeast and fermentation.
Important factors determining the fermentation ability of yeast are the biosynthetic activity of the cells and the ability to adapt to the constantly changing environmental conditions during fermentation.
The biosynthetic activity of cells depends on the nutrition of the yeast, their age and the physicochemical conditions of the environment.
Physiologically active yeast can be obtained only in the absence of nutritional deficiency. Nutrient deficiencies increase with the use of small salt malt, insoluble grains, maltose syrup and sugar. This reduces the intensity of the yeast and their reproduction decreases with the rate of fermentation, increases the duration, reduces the final degree of fermentation of the wort. This leads to a change in the taste profile and a reduction in the removal of seed yeast and their physiological activity.
Yeast growth factors
Yeast fermentation
Yeast differ in terms of growth factors, ie. to those substances that are part of the cells but at the same time cannot synthesize them.
Growth factors for all yeast strains are biotin (vitamin B7), pantothenic acid (vitamin B3) and mesoinositol (vitamin B8). Some strains of fermented yeast also need pyridoxine (vitamin B6). In addition to these vitamins, you should pay attention to thiamine (vitamin B1), which is an activator of fermentation. Thiamine stimulates alcoholic fermentation, participates in the synthesis of biomass.
Yeast fermentation products. Practical guide
Pantothenic acid is involved in the synthesis of unsaturated fatty acids, steroids. Biotin regulates the carbohydrate, nitrogen and fat metabolism of yeast. Inositol is involved in membrane lipid synthesis, cell growth and proliferation.
The main mineral components needed for yeast growth and reproduction include nitrogen, phosphorus, potassium, sulfur and magnesium, which make up most of the ash. Cells most often contain nitrogenous substances, mainly proteins, free amino acids, nucleic acids. Amino acids in wort are most often used for their synthesis from yeast. They can also assimilate inorganic nitrogen (NH4 +), which is converted from cells to amino acids. For normal metabolism, 1 w must contain at least 140 mg of amine nitrogen.
It should be remembered that yeast do not use nitrates, nitrites and amino acids of proteins.
See grape yeast
The metabolism of phosphorus, potassium and magnesium is closely related to nitrogen metabolism. Phosphorus is part of nucleic acids, ATP, phospholipids, cell wall polymers, it can accumulate in the cell as polyphosphates.
Potassium is found in yeast in significant amounts, up to 4.3% of the CB. This is comparable only to the content of nitrogen (up to 10% of CO) and phosphorus (up to 5.5% of CO), which shows its important role in yeast metabolism.
Potassium not only acts as a coenzyme but also enters some cellular structures. It is also involved in regulating the transport of ions across the cell wall and through the mitochondrial membrane. Potassium activates about 40 different enzymes, stimulates the fermentation of maltose and maltotriose.
It is closely related to yeast growth and fermentation rate.
Dr. Yotker's yeast
Magnesium is of great importance in the energy metabolism of yeastassociated with cell growth and multiplication. Sulfur, which is involved in the synthesis of amino acids such as cysteine and methionine, is needed for normal yeast reproduction. A small amount of sulfur needed to produce sulfo and some coenzymes such as biotin, coenzyme A, lipoic acid and thiamine peridoksin.
For trace elements that are essential for yeast growth are: Ca, Mn, Fe, Co, Cu, Zn (Table 1.3). Elements that are rarely required for growth: B, Na, Al, Si, Cl, V, Cr, Ni, As, Se, Mo, Sn, I.
The need for micronutrients can increase several times when the crop is under stress, for example by raising the temperature above the optimum temperature.
Aeration of the nutrient medium is used to obtain a pure culture of yeast and at the beginning of fermentation. Air oxygen is needed for yeast for energy metabolism and synthesis of unsaturated fatty acids and ergosterol.
Quality of fermentation
The physiological state of the yeast determines the flocculation ability of the yeast; the rate and degree of fermentation of wort (fermentation activity); synthesis of fermentation by-products.
Yeast and mold under a microscope
Flocculation is a reversible aggregation of yeast cells. This property of yeast is associated with such indicators as the degree of fermentation of wort, the organoleptic properties of beer, as well as its biological and colloidal resistance.
Yeast - fermentation activity determines the length of the main fermentation, the physicochemical properties of the product, its biological and colloidal stability and sensory profile, as well as its storage stability.
As the concentration of glucose in the medium increases, the rate of fermentation of wort decreases. But this phenomenon does not always occur, as there are strains of yeast in which glucose repression does not occur.
The activity of yeast fermentation is interrelated with the speed of their reproduction, which is important for the rapid fermentation of wort. Cell growth and rapid proliferation depend on the composite balance of the wort (the content of α-amino nitrogen, growth factors and some trace elements), the presence of dissolved oxygen (more than 8 mg / dm3).
Long-used yeasts, as well as yeasts that are not well preserved, have low fermentation activity.
Effect of alcohol
Alcohol is formed during fermentation and its effect on yeast is defined as stress with ethanol. The resulting alcohol inhibits both the rate of yeast reproduction and the fermentation process.
The toxic properties of ethanol are the result of increased permeability and porosity of the cell membrane, which leads to problems with the transport of nutrients. In addition, there is a shortage of available cytoplasm from water.
When the ethanol content in the medium is above 1.2%, the specific growth rate of the yeast decreases. An alcohol concentration in the middle of 2% or more leads to a reduction in biomass yield. Full yeast growth is inhibited when there is 8-9.5% ethanol.
Ethanol also affects the duration of yeast cell generation. Increasing the ethanol concentration from 0 to 1% increases the generation time from about 2.3 to 3.5 hours and at an ethanol concentration of 3.8% already 6.9 hours.
Maya and temperature
Temperature has a significant effect on the energy and structural metabolism of cells and therefore affects the specific growth rate of yeast and the time of generation.
Cells may experience temperature stress (shock). This effect is manifested if yeast are exposed to a sufficiently high (but not higher than 37 ° C) temperature for a short period of time.
It has been found that cells that have survived the effects of high temperatures acquire not only thermal stability but also resistance to alcohol and osmosis.
The mechanical load occurs as a result of the action of high shear stresses during the mixing of the yeast, as they are pumped from one container to another with pumps. Such mechanical operations can "tear" the surface layer of the yeast cell membrane, which reduces the flocculation properties of the cells. In turn, this leads to disturbances in the fermentation process.
The vitality of yeast is understood as their activity or ability to recover after physiological stress.
Factors that reduce the physiological state of the yeast
The main reasons for the deterioration of the physiological condition of the seed yeast can be:
- late release of yeast after their deposition at the bottom of the CCT;
- increasing the shelf life of yeast;
- insufficient mixing of yeast;
- violation of the temperature during storage of yeast;
- Improper handling of yeast during storage;
- selection of storage medium, eg in water;
- mixing (excludes oxygen);
- low pressure storage of carbon dioxide.
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