Yeast

Abstract

Hopped wort is the raw material from which beer is fermented by yeast. As a result of fermentation there is a sea change in the character of the beverage from a sweet, rather bland and satiating drink (wort) to one that has delighted humankind for millennia (beer). Four changes accrue that define this transformation; broadly they are (1) the removal of sweetness by yeast action and its replacement with alcohol; (2) the formation of acids by yeast action and removal of buffers and hence the lowering of pH; (3) carbonation caused by the formation of CO₂ by yeast action and (4) formation and release of a host of metabolic waste products, each in low concentration. In this way yeast magnificently enhances and reveals the fundamental flavor of beer derived primarily from malt and hops.