Q. What are yeast?

Yeasts are unicellular fungi, which are widely distributed in nature. They are somewhat larger than bacteria. The cell length is about 10μm and the diameter is about a third of this. Most yeast is spherical or ellipsoidal. Yeasts that multiply by means of ‘budding' are known as ‘true yeasts'. Yeasts grow luxuriously at a moderate temperature in a solution of sugar in plenty of water.

Under suitable conditions the sugar is converted into alcohol and carbon dioxide is evolved. This is the reason that carbon dioxide is evolved from food materials spoiled by yeasts and pushes out corks from bottles with great force. Most of them do not develop in media containing more than 66% sugar or 0.5% acetic acid. Boiling destroys the yeast cells and spores completely. Some of the yeasts, which grow on fruits, are Saccharomyces, Candida and Brettanomyces.