What is yeast?

We explain what is yeast, alcoholic and lactic fermentation. In addition, its various uses and the types of yeast that are traded.

1. What is yeast?

A diverse set of fungi , usually microscopic and unicellular, capable of initiating the decomposition (fermentation) processes of different organic substances, particularly sugars and carbohydrates, is called yeast or ferment , obtaining as a byproduct other specific substances (such as alcohols).

Yeasts are of different types and exist in different habitats, reproducing both sexually (by spores) and asexually (by budding or sprouting). In a nutritionally favorable environment, a new litter of them is produced in just 90 minutes, since they are simple and effective organisms .

The fermentation is the process that this type of fungus carried out for energy, and generally can be of two different types, according to the product obtained:

1. Alcoholic fermentation . It is an anaerobic decomposition process (in the absence of oxygen) that converts carbohydrates carbohydrates (glucose, sucrose, fructose, etc.) into alcohol (ethanol), along with carbon dioxide (CO2) and two molecules of ATP (Adenosyntriphosphate) , according to the following chemical equation:C6H12O6 + 2Pi + 2 ADP + 2 NAD → 2CH3-CH2OH + 2 CO2 + 2 ATP + 2 NAD

2. Lactic fermentation . This type of fermentation is carried out by some organisms (protozoa) and animal tissues, also in the absence of oxygen (sometimes as a process of obtaining emergency energy in muscle tissue) and glucose breakdown (glycolysis) occurs. and reduction of pyruvate, thus obtaining less energy and byproducting lactate, as waste substance. Everything is given by the following chemical formulas:C6H12O6 + 2Pi + 2 ADP + 2 NAD → 2 C3H4O3 (pyruvate) + 2 ATP + 2NADH + 2H + + 2H2O

2 C3H4O3 + 2NADH + 2H + → 2 C3H6O3 (lactate) + 2NAD

2. What is yeast for?

Yeast is widely used by humans in various industrial and economic processes, in addition to biotechnology. For example, in the preparation of bread, in the preparation of alcoholic beverages such as beer and wine, or in the production of birch sugar.

Many types of yeasts naturally secrete antibiotics, to combat their microscopic enemies, so they are used to obtain these substances for medical and pharmaceutical purposes.

As if that were not enough, the biological simplicity of yeasts makes them ideal for experimentation in the genetic and protein field , since they are cheap, easy to reproduce and simple in their cellular functioning.

3. Types of yeast

Commercially, four types of yeast are handled (especially for bakery work), which are:

• Compressed yeast . It is also known as fresh yeast, because it must be kept cold and is pressed into blocks of pasta. It must be diluted in water before use, and is usually composed of bacteria of the Saccharomeces cerevisiae type  . 
• Dry yeast . Similar to the press, but in vacuum-sealed, dehydrated and granulated (powder) presentations, they can be added directly to the bread dough. In addition, it usually has longer expiration times.
• Natural yeast . Called “mother dough”, it should be left at rest on a piece of bread dough, before using it in the whole preparation.
• Chemical yeast . By chemical substances such as baking soda and baking powder, the same effect is achieved as with biological yeasts, by means of an artificial emulsifier that is usually incorporated in some leavening flours. It is not really a yeast, therefore.