Yeast

Types

Yeast is the most important ingredient in the brew. It is a fungus which is a living microbiological organism. It lives off of the other ingredients that are put in the batch, by metabolizing and reproducing. Although there are hundreds of strains of yeast, only two main varieties are used in beer. These are:

. 1. ale yeast

. 2. lager yeast

Ale yeasts are sometimes termed "top-fermenting" yeasts. This is because they tend to flocculate at the surface of the beer in the begining of the fermentation process. Ale yeasts prosper in the temperature range of 55 to 75 degreef F.

Lager yeasts are termed "bottom fermenting" because they flocculate and then settle to the bottom of the fermenter. A temperature range of 32 to 55 degrees F best suits this type of yeast.

Life Cycle

Throughout the fermentation, yeast is going through its own life cycle. This includes:

. 1. Respiration

During this period, yeasts gain and store energy for reproduction and other activities. Yeasts can gain energy from oxygen and sugar.

. 2. Reproduction

Yeasts are single cell organisms that reproduce through budding.

. 3. Fermentation

During this part of the life cycle, yeast expends energy by converting sugars to alcohol, carbon dioxide and distinct flavor. At this time, the yeast is dispersed and in a state of suspension in order to obtain maximum contact with the liquid beer mixture.

. 4. Sedimentation

At this stage, the yeast runs out of food and energy. It gathers and then settles, essentially shutting down all activity.

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