Foam rising upon beer, or other malt liquors, when fermenting, and used as leaven in making bread and in brewing; yeast.

Verb: to pitch yeast. Noun: kraeusen or the foam on the top of a mug of beer.

Liquid yeast appearing as froth on fermenting beer.

the foamy yeast that appears on the top of malt liquors as they ferment; ale barm was commonly used as the yeast element in breads and batters.

a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey

The foam on the top of a fermentation tank generated by the fermentation process.

Barmhttp://etymonline.com/?search=barmy Online Etymology Dictionary (a common Teutonic word) is defined as scum formed at the top of malt liquor after fermentation; yeast used to leaven bread; or (as a verb) to set up fermentation in liquor. It is also used in the UK to describe a certain bread.