A microorganism used in fermentation, baking, and brewing. The term covers both the organism itself and products containing it.
You need yeast to make bread.
Yeast is used in brewing beer.
Add yeast to the dough and mix well.
This bread is fermented using natural yeast.
If the temperature is too low, the yeast doesn't work well.
酵母 is a living microorganism (yeast) used in fermentation, while 酵素 is a chemical substance (enzyme) that catalyzes reactions; the words sound similar but refer to different things.
酵母 (yeast) is a separate microorganism used for alcoholic fermentation, while 麹 is a mold that first breaks starch down into sugar before yeast can act on it.
酵母 is counted with 株 when referring to distinct strains, as in パン酵母を三株分離した.
The kanji 酵 means 'fermentation' and 母 means 'mother', reflecting the role of yeast as a starter or agent of fermentation. The reading こうぼ is the on'yomi for both characters.
brewer's yeast; brewery yeast