About Real Ale
What is beer?
Beer is produced from malted barley, yeast, water and nearly always with hops, although other ingredients such as wheat, oats, rye, fruit, honey, herbs, spices and flowers are sometimes used. The yeast ferments sugars generated from the malted barley into alcohol and carbon dioxide gas. Hops provide bitterness and characteristic aromas and tastes.
The flavour of the beer depends on many things, including the types of malt and hops used, other ingredients and the yeast strain.
What is real ale?
In the early 1970s CAMRA coined the term 'real ale' for traditional draught cask beers to distinguish them from processed and highly carbonated beers being promoted by big brewers.
CAMRA defines real ale as beer that is produced and stored in the traditional way and ferments in the dispense container to produce a reduction in gravity. It is also dispensed by a system that does not apply any gas or gas mixture to the beer other than by the traditional Scottish air pressure system.
What happens inside a cask of real ale?
Real ale finishes fermenting, conditioning and maturing in the container from which it is dispensed. For this to occur effectively, the beer must contain enough live yeast and fermentable sugar when it is put into dispense containers. This applies for casks of draught real ale and also bottle-conditioned beers, known as real ale in a bottle. Finings are usually added to casks to encourage yeast settlement, enabling clear beer to be drawn from above the sediment; however, some brewers produce unfined cask real ales, which may be served hazy.
Casks are vented to atmospheric pressure in the temperature-controlled environment of a pub cellar (ideally 12-14 degrees centigrade). This allows some carbon dioxide gas from the fermentation to escape, retaining the correct amount for a natural carbonation, or sparkle. The maturation process develops the wonderful tastes and aromas that processed beers can never provide.
As real ale is drawn from casks, usually using handpumps or sometimes direct by gravity, it is replaced by air – no other gas is applied to real ale. The shelf life of real ale, once on dispense, is limited to a few days. This is because of the ingress of air (specifically oxygen) into casks and the gradual loss of carbon dioxide from the beer. Over time the oxygen makes the beer start to taste stale and vinegary because of oxidation, and the loss of carbon dioxide makes the beer taste flat.
What is needed for fermentation in dispense containers?
Some brewers excessively limit the amount of yeast in dispense containers to reduce settling time and ease handling. But the settling time generally enhances flavour maturation and is an essential contribution to the character of real ale.
At least 0.1 million live yeast cells per millilitre of beer are needed to produce a normal amount of natural carbonation (around 2 grammes of carbon dioxide per litre, or 1.1 volumes per volume).
There also needs to be enough fermentable sugar. As sugar is broken down in fermentation, the gravity of the beer drops. A drop of 1-2 degrees of specific gravity (for example, from 1008 to 1007 or 1006) over the life of a cask is enough to demonstrate that sufficient fermentation is occurring.
So in summary, to be classed as real ale, when beer is put into dispense containers it must contain at least 0.1 million cells of live yeast per millilitre and enough fermentable sugar for a drop of 1-2 degrees of gravity.
Why isn't all beer real?
Some draught beers are not classed as real ale. Brewery-conditioned beers, including keg and most craft keg beers, are matured in the brewery and then filtered, which removes the yeast and stops fermentation. No settling time is needed in the cellar and the shelf life is longer. Some brewery-conditioned beers also undergo pasteurisation by heat treatment. Filtration and pasteurisation tend to remove much of the taste and aroma associated with real ale.
Brewery-conditioned beers are dispensed under pressure from sealed containers. There is no natural carbonation because there is no secondary fermentation in the dispense container. Carbon dioxide gas is usually added during dispense, often mixed with nitrogen. Brewery-conditioned beers are often served at lower temperatures than real ale. This, together with the elevated pressures usually involved, results in higher levels of carbonation than are normal for real ale.
Cask-conditioned beers are also sometimes dispensed with the addition of carbon dioxide and/or nitrogen to extend the shelf–life on dispense. This is also not classed as real ale.
Ale and Lager
There is a huge range of different beer styles, but each falls into one of two main categories - ale or lager.
Ales, which include bitters, milds, stouts, porters, barley wines, golden ales and old ales, use top-cropping yeast (saccharomyces cerevisiae). This forms a thick head, and the process is quite short, vigorous and carried out at higher temperatures than lager, typically 18-24 degrees centigrade. This is the traditional method of brewing British beer. Specialist yeasts, including wild yeasts, can be used to produce some styles.
Lagers are brewed with mostly very lightly kilned malt, which produces different flavour characteristics from the pale malt used in ales, specific varieties of hops and bottom-cropping yeast (saccharomyces uvarum). This does not form the thick yeast head associated with ale fermentations and fermentation takes place at a relatively low temperature (10-15 degrees centigrade). Authentic lagers then undergo a long period of cooled conditioning in tanks.
More details about the features of different beer styles are available in the CAMRA Beer Style Guidelines. These apply equally to real ales and other classes of beers.