Yeasts: what are they, types and examples

As we have just said, yeasts are not a derivative of other biological products or a mineral ingredient: yeasts are microscopic fungi , usually single-celled. Although the appearance of fungi in our food products generally makes us think that it is not good, it is not the case with yeasts, which have been used in a controlled way for thousands of years. The yeast or leaven is so important and helpful to us for its ability to carry out the decomposition of sugars and carbohydrates in a process known as fermentation. There are two types of fermentations , and in them the resulting by-products change:

• In alcoholic fermentation , which occurs only under anaerobic conditions, that is, in the absence of oxygen, yeast breaks down sugars into ATP, which is the energy it needs, in addition to CO2 and alcohol as waste products.
• In lactic fermentation , which also occurs anaerobically, lactate is produced as a waste product and lower energy is achieved. This process is sometimes seen as one of the last ways to obtain energy in muscle tissue, and it is also common in the production of many dairy products.

Thus, to give an example, when yeast causes alcoholic fermentation in, for example, a bread dough, CO2 forms gas bubbles that make the dough grow in size, a process that is also helped by the alcohol produced, which evaporates.

On a regular basis and referring to what is available to everyone, there are four main types of yeast that are used in common. At the laboratory level, many more are handled, but when we talk mainly about cooking and what can be purchased in any large surface area, these are the main types of yeasts :

Natural yeast

It is the so-called “sourdough” commonly used in the production of artisan bread. It is left to rest next to a piece of bread dough, in which it grows and develops, before adding it to the rest.

Fresh or pressed yeast

It is called fresh yeast, mainly, because its conservation must be carried out in a cold environment, such as the refrigerator, between 4ºC and 6ºC. It comes in blocks of dough or pressed dough and is made up of the single-celled fungus Saccharomeces cerevisiae . Before using it, it is necessary to dilute it in water for its correct operation.

Dry yeast

In the middle of World War II, Fleischmann developed a type of active and dry yeast to which he gave his name. This yeast, dehydrated and in granules, did not need to be kept cold and its shelf life was much longer than that of fresh yeast. Of the month that the fresh one lasts, the dry yeast extends the period to more than a year. In addition to all this, dry yeast rises or rises twice as fast when used in bakery.

Chemical yeast

This is not actually yeast, but it is so called because it is a chemical emulsifier capable of replicating the effect of yeast. These are products such as bicarbonate, which react to the heat of baking and artificially reproduce the rising effect of yeast. The baking powder only works once in the oven and does not leave the dough before.

There are a large number of yeast species. Some are used in the food industry on a regular basis, while others are more common to find in nature. Here are some examples of yeasts :

• Schizosaccharomyces
• Saccharomyces
• Kluyveromyces
• Zygosaccharomyces
• Pichia
• Debaromyces

It is known that humans have been using yeasts for thousands of years, since the ancient Egyptians began to use them in making bread and beer . It is believed that its discovery must have been made by chance, for example, by leaving a dough exposed for longer than usual before baking, and the yeast naturally present in the flour carried out the fermentation. Currently, yeast is used in the production of all kinds of bakery and pastry products , as well as in the production of fermented alcoholic beverages , such as wine and beer.

Thus, it is a key factor in the history of human nutrition, present in many of our basic products. As if this were not enough, yeast is a probiotic food of the first order, and its consumption offers a large number of benefits in the body.

If you want to learn more about fungi, such as yeasts, we recommend this other AgroCorrn article about the Fungi Kingdom: what it is, characteristics, classification and examples .