Phoenix Facts

Yeast

Two types of yeast are used in the manufacture of beer, Bottom-fermenting yeast (used for low temperature fermenting) and Top-fermenting yeast (used for higher temperature fermenting). Any yeast is a micro-organism of the fungus family and is therefore an "active" ingredient.

Yeast strain and fermentation are as critical to brewing as grape variety is to wine. Yeast is added to the cooled wort in a fermenting vessel. It feeds off the sugars and nutrients extracted from the malt, producing carbon dioxide and alcohol. When most of the sugars have been used up, the yeast becomes inactive and the fermentation is complete.

Domestic draught beers are not pasteurized, and in some instances are not filtered. Many types of wild yeast present in the air can grow on or in the tap or in the keg. These yeast are not necessarily true beer spoilers, but they can cause surface growth if the lines are not cleaned and maintained, or if the beer warms above 50 degrees.

The beer can provide an excellent food source to promote the growth of these organisms, which can exist for long periods of time in the beer lines. These lines, when used, will introduce any organisms present into the freshly tapped keg. Yeast can appear as either a heavy surface film, or as a white colored substance.