Everything you need to know about... yeast

In the latest in our series Nigel Huddleston looks at the role yeast plays

What is yeast?

While the tangible nature of barley and hops makes their contribution to beer easier to comprehend, the role of yeast is more mysterious.

Yeast is a single-celled fungal organism which can be cultivated in laboratories but which also occurs naturally. Aside from brewing it’s a key element in baking bread, where it contributes to making bread ‘rise.’

In brewing, it is used to turn the sugars formed during the mashing process into alcohol and carbon dioxide, the process known as fermentation. As well as producing alcohol and CO2, the action of enzymes in the yeast on the sugar help to create some of the common flavour compounds found in beer.

These are known as secondary flavours as opposed to a flavour given to a beer by hops or other raw ingredients, which are primary flavours.

A yeast cell is composed of walls of cellulose surrounding living matter called protoplasm. It is capable of reproducing itself, which it does during the fermentation process, meaning that a batch of yeast can be used more than once.

Yeast has to be cultivated and carefully stored to keep it in its best condition, which is why cleanliness is paramount in breweries. Contaminated yeast has to be replaced.

Yeast banks in major brewing countries keep samples of most strains that are in use, which brewers can use to replenish stocks or buy different strains to make different styles of beer.

Yeast in brewing

Although brewers have been using yeast for centuries the science behind it .....

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By Nigel Huddleston

Section : Beer Production

Page number : 58