General English


  • noun a single-celled fungus that is used in the fermentation of alcohol and in making bread


  • A microorganism (strictly speaking a fungus) which reproduces by budding from the parent microorganism. The most important in cooking is Saccharomyces cerevisiae which has a multitude of variants used principally for converting sugars to alcohol or water and carbon dioxide as in beer, wine, and bread production. Yeasts can also excrete some enzymes which break down polysaccharides into simple sugars. Yeasts work best around 30 to 35°C and are killed above 60°C.


  • noun a fungus which is used in the fermentation of alcohol and in making bread. It is a good source of vitamin B.


  • noun a living fungus used to make bread and beer


  • a microscopic organism that causes the fermentation process to occur. Wild yeasts are present on the skins of grapes and would start the fermentation process of grape juice naturally, converting natural sugars in the juice into alcohol, but winemakers normally add cultivated yeasts to the grape juice to provide more control over the fermentation process. Yeast cannot exist when the level of alcohol is above around 16 per cent in wine, which is why alcohol such as brandy is added to a wine to stop fermentation and produce a fortified wine.

Origin & History of “yeast”

Yeast is etymologically a substance that causes ‘fermentation’. For its ultimate source is the Indo-European base *jes- ‘boil, foam, froth’, which also produced Greek zeī́n ‘boil’ (source of English eczema) and Welsh iās ‘seething’. Its Germanic descendant produced German gischt ‘yeast, froth’, Dutch gist, gest ‘yeast’, and English yeast.