Beer is usually used to refer to any alcoholic beverage derived through the fermentation (but not distilled) of starchy material. This process is called brewing. One of the oldest beverages, beer dates back to at least the 5th millennium BCE. The oldest written records of beer are from Ancient Egypt and Mesopotamia.
The sheer variety of beer can be overwhelming to the novice beer connoisseur, and each variety of beer is said to belong to a particular 'style'. A beer's style is what describes the overall flavor and often the origin of a beer. The greatest variety of beer can be found in Belgium.
A major element in determining the type of beer is the yeast used during the fermentation process. Most beer styles fall into one of two large families: ale, using top-fermenting yeast, or lager, using bottom-fermenting yeast. Beers that blend the characteristics of ales and lagers are referred to as hybrids.
An ale is any beer that is brewed using only top-fermenting yeasts, and is generally fermented at higher temperatures than lager beer (15–23°C, 60–75°F). Ale yeasts at these temperatures produce significant amounts of esters and other secondary flavor and aroma products, and the result is a beer with a slightly "flowery" or "fruity" aroma and flavor.
Lagers are the most common category of beer. Their origin is of Central Europe. Lager yeast is a bottom-fermenting yeast, and typically undergoes primary fermentation at 7-12°C, and then is taken through a longer secondary fermentation at 0-4°C. The cooler secondary stage results in crisper tasting beer, and allows the lager to clear and mellow.