Refers to foam on the top of the beer. The foam head should be thick, dense and tight for most beer styles. Some terms for describing a beers head are; persistent, rocky, fluffy, dissipating, lingering, frothy, tight, dense, smooth
Yeast are micro-organisms, spoor fungi, which activate the fermentation process converting malt sugar to alcohol and carbon dioxide. Yeast additionally create the flavor elements which contribute to the creation of the taste of beer.