Styles of beer

One fundamental approach to classifying beers is based on whether they are generated by 'top fermentation' or 'bottom fermentation', i.e. whether the yeast congregates at the top of the vessel or sinks to the base. In modern fermenters with their high hydrostatic pressures the distinction is blurred. Top fermentation tends to be at relatively warm tem­peratures (15-25°C) with the yeast producing higher levels of avour volatiles such as esters, affording fruity characteristics. Bottom fermentation beers are produced at much lower temperatures (e.g. 6-15°C) and frequently possess signi cant sulphury notes.
The main top fermentation beers are the ales. Alcohol content will generally be in the range 3 to 7.5% by volume (ABV), and more frequently in the bottom half of the range. The major grist material will be well-modi ed malt, kilned to relatively high temperatures to impart a copper colour. 'Mild' is a sweeter, darker product, the colour being either due to caramel or in part to a low proportion of heavily kilned malt, though not so much as to impart burnt avours. It tends to have a lower alcohol content (less than 3.5% ABV) and when bottled may be referred to as 'Brown Ale'. 'Barley wines' are fermented at very high gravities and so develop much higher alcohol contents (up to 10% by volume). They are usually sold in smaller volumes, in bottles called 'nips'.
Porters (named after the main customers in eighteenth-century London) are tradi­tionally very dark, due to the use of a proportion of roasted barley in the grist, and not overwhelmingly strong (about 5% ABV). Stouts are close relatives of porter, originating in Ireland, with intense colour and burnt, smoky avours due to the use of roasted barley adjuncts, and high bitterness. These robust avour characters are frequently mellowed by the use of nitrogen gas, which 'smoothes' the palate as well as affording the rich, white and creamy foam. Alcohol content may be between 4 and 7%, with up to 10% in Imperial stouts. Sweet stouts are a British variant, of lower alcohol content (up to 4% ABV), with less roast character (often due to the use of caramel and less roast barley as colourant). Trappist beers, from Belgium, are relatively dark, intensely bitter, acidic products of up to 12.5% alcohol by volume. Lambic and gueuze have very complex avours, owing to the use of a more complex micro ora than brewing yeast alone. They are sour (low pH) and usually hazy. Various avourants may be added, includ­ing cherries (Kriek) or raspberries (Framboise). The German wheat beers comprise a further class of top fermentation beers. Weizenbier is made from a grist of at least 50% wheat malt. The products are relatively highly carbonated, affording a refreshing nature alongside the fruity and phenolic (clove-like) characters. Often they are cloudy due to yeast, which is employed traditionally to carbonate the bottled product through 'natural conditioning'. The products are relatively lightly coloured (straw-like) and have alco­hol contents of 5-6% by volume. Weissbier ('white beer') is much weaker (e.g. 2.8% alcohol by volume), made from a grist of less than 50% wheat malt, with the addition of lactic acid bacteria to generate a low pH of 3.2-3.4. Therefore such beers are quite sour, and may be taken with raspberry or sweet woodruff syrups.
The classic style of bottom fermentation beers originated in Pilsen and is known as Pilsner. It is quite malty with typically 4.8-5.1% ABV and a pale gold colour. Particularly important is the 'late hop character', which is introduced by retaining a proportion of the hops for addition late in the kettle boil. The term 'lager' is used by many, inaccurately, as a synonym for Pilsner. Lager as a term is really an umbrella description for relatively pale beers, fermented and dispensed at low temperatures.
Malt liquor is a term used to describe alcoholic products (6-7.5% ABV) which are very pale, very lightly hopped and quite malty and sweet.
Light beers comprise the most rapidly growing segment of the beer market. 'Standard' beers retain a proportion of carbohydrate that is not fermentable by yeast, whereas a light beer has most or all of this sugar converted into alcohol. These beers therefore have fewer calories, provided that the extra alcohol is diluted to the level found in 'normal' beers.
There are many de nitions worldwide about what constitutes low-alcohol products. Perhaps the most stringent is in UK, where non- and low-alcohol beers (NAB/LABs) contain less than 0.05% or 1.2% ABV, respectively. They are produced either by remov­ing the alcohol from a full-strength brew (by techniques such as vacuum distillation or reverse osmosis), or by restricting the ability of yeast to ferment wort (either by making a wort containing very low levels of fermentable sugars or by ensuring that the contact between yeast and wort is at a very low temperature and for a relatively brief time).