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The science of alcohol
The science of alcohol

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4 Conditioning and storage of beer

The very final stage in the brewing process is to consider how the beer is going to be stored prior to sale. After the initial or primary fermentation, beer is conditioned, matured or aged in one of several ways which can take from two to four weeks, several months, or several years, depending on the brewer’s intention for the beer.

The conditioning process is itself a function of the yeast. Following the primary fermentation, the majority of the wort sugars have been converted to alcohol, and a lot of the yeast goes dormant because there is no more food for it; but there is still yeast activity. The conditioning process allows time for a secondary fermentation. Here the yeast starts to use the by-products of the primary fermentation as a food source. Examples of such by-products include ketones that have buttery and honey-like flavours. These compounds are considered flaws when present in large amounts in beer and can cause stability problems during storage, leading to off flavours. Acetaldehyde is an example of a primary fermentation by-product that has a pronounced green apple smell and taste. It is an intermediate compound in the production of ethanol and is harmful. The yeast reduces compounds such as these during the secondary fermentation process, making the beer safer.

Towards the end of secondary fermentation, the suspended yeast settles out and the beer starts to clear. This process can be helped by chilling the beer, very similar to what happens in the lagering process. In the case of ales, this process is referred to as ‘cold conditioning’ and is a popular practice at most microbreweries for the production of craft beers. Cold conditioning for one week is usually sufficient.