History, culture, geography, time and marketing can all influence our perception of a style of a beer. The beer family is also large and expanding, and the home brewer and beer drinker can choose from an impressive and growing range – ales, lagers, lambics, stouts, porters and wheat beers. But it doesn’t stop there.
Beers made with herbs, spices and fruit can all be found. Some are dark, some are light, some are sweet, some are sour, some are clear, others are cloudy. The extent of the family is limited only by the imagination of the brewers.
However, the family of beer has two broad branches – lager and ale. These two extensive classes are broadly defined by the yeast strain which is likely to have been used during fermentation: Saccharomyces pastorianus, which is often called Saccharomyces carlsbergensis, is used to make lagers, while Saccharomyces cerevisiae is the yeast from which most ales are produced.
Lager is the world’s most popular beer style, though it could be argued it’s a production process rather than a style. The word ‘lager’ means to store at a cold temperature, and such beers are traditionally fermented at cooler temperatures than other beers, at between 5–9°C, and then matured or stored at close to freezing, ie 0°C – though today some brewers are using warmer fermentation temperatures for their lagers.
Lager beers are often described as bottom-fermented, but bottom-cropping would probably be a better description, as during part of its lifecycle the yeast cell feeds off the sugar in the sweet wort, producing ethanol alcohol and carbon dioxide.
The yeast ferments at all levels throughout the liquid, but once its work is done it collects at the bottom of the fermenting vessel. Once settled, the brewer can easily drain the beer away, leaving a bed of yeast, and if needed some of this can be ‘cropped’ for use in the next fermentation.
Ales are traditionally beers that depend on warmer fermentation than lager-style beers, using a yeast that rises to the top of the brewing vessel, where it can be cropped and removed, though eventually it will fall to the bottom. Members of the ale family are typically fermented at 15–25°C.
Top-fermenting (cropping) yeasts are used for brewing ales, porters, stouts, alts and kölschs, while bottom-fermenting (cropping) yeasts are used for Pilsners, Dortmunders, märzen and bocks.
Within the family of beers there’s also a third broad style – beers which are fermented after exposure to the air, which allows wild yeasts and bacteria to infect them. Some call this natural fermentation, where no selection of yeast has taken place.
The resulting flavour is dependent on the actual microorganisms but is normally quite tart and tongue-tingling. The lambic beers of Belgium are probably the best-known examples of spontaneous fermentation.
Some breweries actually use a commercially available wild yeast, like Brettanomyces Bruxellensis, to create more complex beers, often with dry, vinous and some cidery flavours and a tart sourness.
