The modern theory of beer style is largely based on the work done by the late writer Michael Jackson in his 1977 book The World Guide To Beer in which Jackson categorised a variety of beers from around the world in local style groups suggested by local customs and names. Fred Eckhardt furthered Jackson's work publishing The Essentials of Beer Style in 1989.
However, there has been differentiation of beer since around 2000 BCE, which has continued throughout history and within many different cultures. While the systematic study of beer styles is a modern phenomenon, the act of beer differentiation itself is ancient and widespread.
The study of what constitutes a beer's style can be broken down into various elements. These may include the amount of bitterness imparted to a beer from bittering agents such as hops, roasted barley, or herbs; the amount of sweetness from the sugar present in the beer; the strength of the beer from the amount of fermentable material converted into alcohol; the smoothness or viscosity of the beer in the mouth, commonly described as mouthfeel; and the appearance of the beer, including the colour.
Documents in various countries over the years reveal comments on different local brewing methods or ingredients. Pliny the Elder in his Naturalis Historia wrote about Celts brewing ale "in Gaul and Spain in a number of different ways, and under a number of different names; although the principle is the same." Anglo-Saxon laws reveal they identified three different ales, while the Normans mention cervisae (ale) and plena cervisia (full bodied ale) in the Domesday Book.
By the 1400s brewers in Germany and the Low Countries were using hops to flavour and preserve their ale – this new style of ale was called beer. When this trend came to Britain and brewers of beer in Southwark, London, started to take sales away from the traditional brewers of unhopped ale, there were complaints and protests. Various laws were passed favouring either beer or ale for a number of years, until hopped beer became the standard style throughout Europe.
Also in the 1400s, brewers in Bavaria were storing beer in cool caves during the summer months in order to stop it spoiling. The beer became known as lager from the German word lagern, meaning "to store".
Although beers using naturally-dried malt would have been pale-coloured, by the 1600s most malts in Europe would have been dried over a fire, resulting in a dark coloured beer. When coke started to be used for roasting malt in 1642, the resulting lighter coloured beers became very popular. By 1703 the term pale ale was starting to be used, though the beer it described was a lightly-hopped ale, very different from more bitter modern versions.
However, despite an awareness by commentators, law-makers, and brewers that there were different styles of beer, it wasn't until Michael Jackson's World Guide To Beer was published in 1977 that there was an attempt to group together and compare beers from around the world. Jackson's book had a particular influence in North America where the writer Fred Eckhardt was also starting to explore the nature of beer styles. The wine importing company Merchant du Vin switched to importing beers mentioned in Jackson's book. Small brewers started up, producing copies and interpretations of the beer styles Jackson described.
While North America developed beer styles into a serious study with fixed parameters of bitterness, colour, aroma, yeast, ingredients and strength, other countries continued to mainly categorise beers loosely by strength and colour, with much overlapping of naming conventions.
Many beers are transparent, but some beers, such as hefeweizen, may be cloudy due to the presence of yeast making them translucent. A third variety is the opaque or near-opaque colour that exists with stouts, porters, schwarzbiers (black beer) and other deeply coloured styles. Thickness and retention of the head and the lace it can leave on the glass, are also factors in a beer's appearance.
Original gravity, abbreviated OG, is the density of the wort before the beer has begun fermentation. Roughly, it corresponds to the amount of fermentable material in the beer and can be measured in several ways, such as the Plato scale, Baumé scale, Balling scale, Brix scale, or gravity, with Plato and gravity being the most common contemporary measures.
The original gravity of a beer was the basis for determining taxation in both the UK and Ireland from 1880 until the late 20th century, and a legacy of that system remains in the largely arbitrary division of bitter into "bitter", "best bitter", and "special bitter" substyles.
In continental Europe, the strength of a beer in degrees Plato is sometimes used by the brewery to distinguish a particular beer produced in a line. For example, Rochefort Brewery produces three beers, all dissimilar in colour, flavour, and aroma; and sells them as Rochefort 6, Rochefort 8, and Rochefort 10, the numbers referring to the original gravities of the beers. Westvleteren Brewery, meanwhile, produces three beers, and calls them Blonde, 8, and 12.
Modern strength classification for tax and regulatory purposes often discriminates by alcohol by volume, abbreviated ABV; or the directly-related measure alcohol by weight. Before the development of modern brewing practices and the understanding of the biochemistry of yeast, the final ABV of a beer could not be controlled to great precision and therefore ABV was useless as a determinant for revenue. Contemporarily, though, ABV is used in Great Britain to determine the duty on beer and cider, and sales of beer and cider above a certain ABV is restricted or prohibited; for example, in the US state of Alabama the sale of beer over 6% ABV is illegal; meanwhile, in Texas, beers below 4% ABV cannot be sold as stout regardless of other stylistic considerations.
The final measure of strength, final gravity of the beer, refers to the density of the beer when fermentation has completed. This is a function of the original gravity of the beer, the recipe of the mash and the attenuation of the yeast and determines a large portion of the feel of the beer in the mouth, particularly whether the beer is sweet or dry. The distinction between English and Irish stouts is usually drawn by this, with Irish stouts considered drier; however, absolute final gravity is not so much a determiner as is the final gravity compared to the alcohol content.
Most beers use barley malt as their primary source of fermentable sugars, and some beer styles mandate it be used exclusively, such as those German styles developed under Reinheitsgebot. Some beer styles can be considered varietals, in the same sense as wine, based on their malt bill.
Kilned pale malts form the basis of most beer styles now in production, with styles using other grains as a base, for example bock, which uses Munich malt as a base, distinguished by that. The Rauchbier and Alaskan smoked porter styles are distinguished by the use of smoked malt.
Some styles use one or more other grains as a key ingredient in the style, such as wheat beer, rye beer, or oatmeal stout. Other grains such as corn and rice make less of a flavour contribution and are used primarily as an added source of fermentable sugars.
Alcoholic beverages made from the fermentation of sugars derived from non-grain sources are generally not called "beer," despite being produced by the same yeast-based biochemical reaction. Fermented honey is called mead, fermented apple juice is called cider, fermented pear juice is called perry (sometimes, pear cider) , and fermented grape juice is called wine. Chinese jiu and Japanese sake are made using much the same process as beer with one additional step in the fermentation as well as using rice instead of primarily barley malt.
Ale is beer that is brewed using only top-fermenting yeasts, and is typically fermented at higher temperatures than lager beer (15–23°C, 60–75°F). At these temperatures, ale yeasts produce significant amounts of esters and other secondary flavours and aromas, often resembling those of apple, pear, pineapple, grass, hay, banana, plum or prune.
Principal styles of ale include Barley Wine, Belgian Trippel, Belgian Dubbel, Altbier, Bitter, Amber Ale, Brown Ale, Pale Ale, Kölsch, Porter, Stout, and Wheat beer.
Pale lagers are the most commonly consumed type of beer in the world. Lagers are of Central European origin, taking their name from the German lagern ("to store"). Lager yeast is a bottom-fermenting yeast, and typically begins fermentation at 7-12°C (45-55°F) (the "fermentation phase"), and then stored at 0-4°C (30-40°F) (the "lagering phase"). During the secondary stage, the lager clears and mellows. The cooler conditions also inhibit the natural production of esters and other byproducts, resulting in a "crisper" tasting beer.
Modern methods of producing lager were pioneered by Gabriel Sedlmayr the Younger, who perfected dark brown lagers at the Spaten Brewery in Bavaria, and Anton Dreher, who began brewing a lager, probably of amber-red colour, in Vienna, Austria, in 1840–1841. With modern improved fermentation control, most lager breweries use only short periods of cold storage, typically 1–3 weeks.
Most of today's lager is based on the original Pilsner style, pioneered in 1842 in the town of Pilsen (Plzeň), in an area of the Austrian monarchy now located in the Czech Republic. The modern pale lager that developed from Pilsner is light in colour and high in forced carbonation, with an alcohol content of 3–6% by volume. The Pilsner Urquell or Heineken brands of beer are typical examples of pale lager, with the Pilsner Urquell brand having a hop presence more associated with the pilsner style.
Principal styles of lager include American-style lager, Bock, Dunkel, Helles, Oktoberfestbier / Märzen, Pilsner, Schwarzbier and Vienna lager.
Beers of spontaneous fermentation are ales that use wild yeasts, rather than cultivated ones. All beer was once brewed this way, but by the Middle Ages brewers had learned to crop the yeast from one brew and use it in the next. Only in a few isolated regions were wild yeasts still used. The best-known region where spontaneous fermentation is still used is the Senne Valley in Belgium, where lambic is produced.
Hybrid or mixed style beers use modern techniques and materials instead of, or in addition to, traditional aspects of brewing. Although there is some variation among sources, mixed beers generally fall into the following categories: