For hundreds of years hops have been used as the 'seasoning' in beer. Originally a wild-growing weed, the hop, a member of the cannabis family, is now intensively cultivated. Its inherent poor resistance to disease and its low tolerance of adverse weather conditions have led to the development of many new varieties bred to combat disease whilst retaining flavour and bittering power.
Hops are used for three separate purposes, besides their natural preserving properties. Firstly they impart bitterness. Secondly they combine with the malt to give the beer its flavour. Their third contribution is the wonderful bouquet associated with the finest Real Ales and Pilsners.
To obtain the maximum bitterness from hops, they must be boiled in the wort for a minimum of one hour. The alpha acids, which provide the bitterness are insoluble until they have been isomerised by the long boil. Unfortunately all of the aroma and much of the flavour is driven off with the steam. It is common practice, therefore, to add hops to the boil in stages.
At the beginning of the boil the bittering or 'copper' hops are added. Although much of the flavour disappears during boiling, each hop variety has its own characteristic bitterness. In general high alpha hops give a somewhat harsh bitterness, which could be unpleasant in a heavily hopped beer. These should be used in mildly hopped beers or in Stouts where the main flavour is derived from roasted grains. When brewing beers with a high hop profile, such as Bitters, Pilsners, Altbiers etc., only the finest aroma hops should be employed. Late in the boiling process, about 5 to 10 minutes from the end the flavour hops are added. These should always be aroma varieties. There are several methods used to create bouquet. Certainly only the freshest aroma hops should be used and these can be stirred into the wort when boiling is over and left to steep for a while. Alternatively the beer can be dry hopped after fermentation. This is conducted either in a conditioning tank (secondary fermenter) or in a keg or cask.
Hops are generally divided intro three categories...
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These varieties are usually low in alpha acids but high in essential oils. Brewers wishing to create high class, heavily hopped beers should use aroma hops for all three purposes. The bitterness imparted by aroma hops such as Goldings or Tettnang is totally different from that derived from high alpha varieties such as Northern Brewer or Target.
Some varieties, although high in alpha acids, have quite acceptable aroma properties. These can be used for boiling and late additions but are usually unsuitable for dry hopping.
Use only where low bitterness levels are required. Can be used in dark beers employing large amounts of roasted grain.
Many recipes in home brewing books have been formulated without regard for the alpha acid content of the suggested hops and rarely advise late hopping. This type of recipe will often produce a completely unbalanced beer with precious little hop flavour and aroma and should be used for guidance only. A far better way is to brew to alpha acid values as is practised commercially. The internationally recognised standard for measuring bitterness in beer is the European Bittering Unit (EBU). Most beers fall between EBU 25and EBU 65. The following is a guide to typical EBU levels for the more popular beer styles:
There is a simple formula for determining the weight of hops in grams required to brew to a specified EBU value. This formula assumes a 20% hop utilisation. Some brewers may better this utilisation so adjustments may be necessary.
EBU REQUIRED x BREW LENGTH IN LITRES
ALPHA ACID OF CHOSEN HOPS x 2
EXAMPLE: You decide to brew 25 litres of Bitter at EBU 45 using East Kent Goldings with an alpha acid content of 7.6%. The calculation is as follows.
(45 x 25) / (7.6 x 2) = 74grams
IMPORTANT. Only the 'copper hops' should be included in the above calculation as little or no bitterness will be extracted from late hops.