When we talk about yeast, the first thing that comes to our minds is a delicious and crisp bread. Some of you may also associate it with the production of beer, wine, cheese, yogurt, antibiotics or less pleasant things, like infections. The use of yeast is very ancient and knew how to manipulate them for our benefit even before the invention of the microscope. But, what are exactly yeasts?
First, they are unicellular microorganisms. They are eukaryotes belonging to the fungi kingdom. Fungi do not perform photosynthesis, so they require other sources of energy. They use organic compounds –sugars for example– that metabolize into simpler molecules. It is this metabolism, which is so useful to us to produce wine or bread. This was quickly understood by our ancestors.
One of the most famous yeast is Saccharomyces cerevisiae, the baking yeast. It is a yeast that makes alcoholic fermentation. This means that it metabolizes sugars to turn them into ethanol and CO2. Already since prehistory it was used to preserve drinks and food. There are archaeological records of fermented brews from 7000 BC in China and 5000 BC in Mesopotamia. Something similar happened with bread in ancient Egypt. In fact, we do not know for sure, when we began to use it in a conscious way, but we do know that this ancient process is one of the basis for current biotechnology. Moreover, during these thousands of years we have been selecting and genetically differentiating variants. Long before we fully understood what we were doing.
Thus yeasts seem to be with us from the dawn of mankind. Yeasts are at the base of our diet and who knows, maybe they are the secret ingredient of Grandma's recipe.