In the vast majority of cases, beer falls into two broad types, determined by the time and temperature of the primary fermentation as well as where the yeast sits during fermentation. There are ales and lagers.
Ale is brewed using only top-fermenting yeasts, and is typically fermented at higher temperatures than lager (60-70°F). Ale yeasts at these temperatures produce significant other secondary flavor and aroma products, and the result is a flavorful brew with a slightly "flowery" or "fruity" aroma.
Lagers are the most commonly consumed type of brew in the world. Lagers are of Central European origin, taking their name from the German word ‘lagern’ ("to store"). Lager yeast is a bottom-fermenting yeast, and typically begins fermentation at 45-54°F (the "fermentation phase"), and then stored at 33–39°F (the "lagering phase"). During the secondary stage, the lager clears and mellows. The cooler conditions also inhibit the natural production of other byproducts, resulting in a "crisper" taste. Most of today's lager is based on the Pilsner style, pioneered in 1842 in the town of Pilsen, in an area of what is today the Czech Republic. The modern Pilsner lager is light in color and high in carbonation, with a strong hop flavor and an alcohol content of 3–6% by volume. Pilsner Urquell and Heineken brands are typical examples of pilsner.
Hybrid or mixed styles 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:
- Steam beers were invented by German immigrants living in California and are made with bottom-fermenting (lager) yeasts, but fermented at warmer (ale) temperatures. The name "steam beer" is a trademark of the Anchor Brewing Company, brewers also refer to this type as "California common".
- Fruit and vegetable brews are mixed with some kind of fermentable fruit or vegetable adjunct during the fermentation process, providing obvious yet harmonious qualities.
- Wood-aged are any traditional or experimental brew that has been aged in a wooden barrel or have been in contact with wood (in the form of chips, cubes or "beans") for a period of time (Oak is the most common). Often, the barrel or wood will be treated first with some variety of spirit or other alcoholic beverage--bourbon, scotch and sherry are common.
- Smoked beers are any brew whose malt has been smoked. A smoky aroma and flavor is usually present. The most traditional examples of this style are the Rauchbiers of Bamberg, Germany. However, many brewers outside of Germany--most notably American craft brewers--have been adding smoked malt to their brews.
True Lambics are a unique type produced only in the small Senne Valley region in Belgium. Yeast is not added directly to the wort. The vats are left open and wild yeast, which is unique to the region, is allowed to fall into the vats naturally. This process is called spontaneous fermentation. Different fruits, syrups, and spices are added to produce different styles.
There are several different styles associated with each type which are displayed below.
Charts courtesy of Drinking Beer