| || ||Boiling. Hops are added to the wort which is boiled for up to two hours. Extra sugar is sometimes added at this stage depending on the type of beer required. Boiling extracts the bitter flavour from the hops, stops further enzyme activity, sterilises the wort and, according to the boiling time, controls the strength of the beer. The wort is then strained through filters and cooled to about 20 °C before being pumped into the fermenting vessels. |
Fermentation. The yeast is added to the wort where it grows and converts the sugar to alcohol and carbon dioxide. The temperature is controlled at 8 12 °C to produce lager and 12 21 °C to make ale. An ale fermentation takes 4 6 days, whereas lager production is much slower and takes up to two weeks. During fermentation the yeast population multiplies about six times. The excess is skimmed off. It can be re-used, usually after an acid wash to control any contamination by bacteria, but eventually the yeast performance drops and it is sold on to be made into yeast extract or animal feed.
Downstream processing. Some beers are run into casks where more sugar is added and a secondary fermentation takes place. Keg beer is filtered then pasteurised to kill the yeast. Bottled or canned products are usually filtered and centrifuged before packaging. Some beers are carbonated to improve their sparkle.