Lager (German: storeroom or warehouse) is a type of beer that is conditioned at low temperatures normally in cold storage at the brewery, before being delivered to the consumer. It may be pale, golden, amber, or dark.
Although the defining feature of lager beer is its maturation in cold storage, it is also distinguished by the use of bottom fermenting lager yeast. While it is possible to use lager yeast in a warm fermentation process such as with American Steam beer, the lack of a cold storage maturation phase precludes such beer from being classified as lager beer. On the other hand, German Altbier and Kölsch use traditional top-fermenting yeast and temperatures, but with a cold storage finishing stage; its classification as obergäriges lagerbier (top-fermented lager beer) may be controversial.
Up until the 19th century, the German word Lagerbierreferred to all types of bottom-fermented, cool-conditioned beer, in normal strengths. In Germany today however, the term is mainly reserved for the prevalent lager beer styles of southern Germany. In common parlance, these beers are distinguished by their colors, and referred to as a (Bavarian) "Helles" (pale), or a "Dunkel" (dark), though both words may be used as adjectives to describe other types of beer. The popular Pilsner style, which is more heavily hopped, although it is also a Pale lager, is most often known as simply "Pilsner" or "Pils", and generally is called neither a "Lagerbier" nor a "Helles". Numerous other types of lager beer styles are produced, such as Bock, Märzen, and Schwarzbier.
In the United Kingdom, the term "Lager" commonly refers specifically to pale lagers, many of which are derived from the Pilsner style. Worldwide, pale lager is the most widely consumed and commercially available style of beer. It is often known primarily by its brand name, and labeled simply as "beer". Well-known brands include Budweiser, Stella Artois, Beck's, Brahma, Corona, Snow, Tsingtao, Heineken, Carling, Foster's, and Baltika.
There are numerous lager styles so for now we have focussed the below notes on the 'American Lager' style:
History: Although German immigrants had brewed traditional Pilsner-inspired lager beer in the United States since the mid-late 1800s, the modern American lager style was heavily influenced by Prohibition and World War II. Surviving breweries consolidated, expanded distribution, and heavily promoted a beer style that was appealing to a broad range of the population. Became the dominant beer style for many decades, and spawning many international rivals who would develop similarly bland products for the mass market supported by heavy advertising.
Aroma: Low to no malt aroma, although it can be perceived as grainy, sweet or corn-like if present. Hop aroma may range from none to a light, spicy or floral hop presence. While a clean fermentation character is desirable, a light amount of yeast character (particularly a light apple character) is not a fault. Light DMS is also not a fault.
Appearance: Very pale straw to medium yellow color. White, frothy head seldom persists. Very clear.
Flavor: Relatively neutral palate with a crisp and dry finish and a moderately-low to low grainy or corn-like flavor that might be perceived as sweetness due to the low bitterness. Hop flavor ranges from none to moderately-low levels, and can have a floral, spicy, or herbal quality (although often not strong enough to distinguish). Hop bitterness at low to medium-low level. Balance may vary from slightly malty to slightly bitter, but is relatively close to even. High levels of carbonation may accentuate the crispness of the dry finish. Clean lager fermentation character.
Mouthfeel: Low to medium-low body. Very highly carbonated with slight carbonic bite on the tongue.
Overall Impression: A very pale, highly-carbonated, light-bodied, well-attenuated lager with a very neutral flavor profile and low bitterness. Served very cold, it can be a very refreshing and thirst quenching drink.
Comments: Strong flavors are a fault. Often what non-craft beer drinkers expect to be served if they order beer in the United States. May be marketed as Pilsner beers outside of Europe, but should not be confused with traditional examples.
Ingredients: Two- or six-row barley with high percentage (up to 40%) of rice or corn as adjuncts.
Commercial Examples: Budweiser, Coors Original, Grain Belt Premium Lager, Miller High Life, Pabst Blue Ribbon, Special Export
Source: 2015 BJCP Style Guidelines - http://www.bjcp.org/stylecenter.php, Wikipedia - https://en.wikipedia.org/wiki/Lager