The purpose of brewing is to convert the starch source into a sugary liquid called wort and to convert the wort into the alcoholic beverage known as beer in a fermentation process effected by yeast.
The first step, where the wort is prepared by mixing the starch source (normally malted barley) with hot water, is known as mashing. Hot water (known as liquor in brewing terms) is mixed with crushed malt or malts (known as grist) in a mash tun. The mashing process takes around 1 to 2 hours, during which the starches are converted to sugars, and then the sweet wort is drained off the grains. The grains are now washed in a process known as sparging. This washing allows the brewer to gather as much of the fermentable liquid from the grains as possible. The process of filtering the spent grain from the wort and sparge water is called wort separation. The traditional process for wort separation is lautering, in which the grain bed itself serves as the filter medium. Some modern breweries prefer the use of filter frames which allow a more finely ground grist. Most modern breweries use a continuous sparge, collecting the original wort and the sparge water together. However, it is possible to collect a second or even third wash with the not quite spent grains as separate batches. Each run would produce a weaker wort and thus a weaker beer. This process is known as second (and third) runnings. Brewing with several runnings is called parti gyle brewing.
The sweet wort collected from sparging is put into a kettle, or copper, (so called because these vessels were traditionally made from copper) and boiled, usually for about one hour. During boiling, water in the wort evaporates, but the sugars and other components of the wort remain; this allows more efficient use of the starch sources in the beer. Boiling also destroys any remaining enzymes left over from the mashing stage. Hops are added during boiling as a source of bitterness, flavor and aroma. Hops may be added at more than one point during the boil. The longer the hops are boiled, the more bitterness they contribute, but the less hop flavor and aroma remains in the beer.
After boiling, the hopped wort is now cooled, ready for the yeast. In some breweries, the hopped wort may pass through a hopback, which is a small vat filled with hops, to add aromatic hop flavouring and to act as a filter; but usually the hopped wort is simply cooled for the fermenter, where the yeast is added or pitched. During fermentation, the wort becomes beer in a process which requires a week to months depending on the type of yeast, temperature and strength of the beer. In addition to producing alcohol, fine particulate matter suspended in the wort settles during fermentation. Once fermentation is complete, the yeast also settles, leaving the beer clear.
Fermentation is sometimes carried out in two stages, primary and secondary. Once most of the alcohol has been produced during primary fermentation, the beer is transferred to a new vessel and allowed a period of secondary fermentation. Secondary fermentation is used when the beer requires long storage before packaging or greater clarity. Many modern micro brews also will have the beer go through a cold conditioning period. This allows the flavors to mellow and deepen.
When the beer has finished fermenting and conditioning it is packaged either into casks for cask ale or kegs, aluminium cans, or bottles for other sorts of beer. For bottle carbonated beer a little bit of sugar is added at the time of bottling. Other beer may be injected with carbon dioxide gas or nitrogen gas to give it bubbles.
The basic ingredients of beer are water; a starch source, such as malted barley, able to be saccharified (converted to sugars) then fermented (converted into alcohol and carbon dioxide); a brewer’s yeast to produce the fermentation; and a flavouring such as hops. A mixture of starch sources may be used, with a secondary starch source, such as maize (corn), rice or sugar, often being termed an adjunct, especially when used as a lower-cost substitute for malted barley. Less widely used starch sources include millet, sorghum and cassava root in Africa, and potato in Brazil, and agave in Mexico, among others. The amount of each starch source in a beer recipe is collectively called the grain bill.
Starch = The starch source in a beer provides the fermentable material and is a key determinant of the strength and flavour of the beer. The most common starch source used in beer is malted grain. Grain is malted by soaking it in water, allowing it to begin germination, and then drying the partially germinated grain in a kiln. Malting grain produces enzymes that convert starches in the grain into fermentable sugars. Different roasting times and temperatures are used to produce different colours of malt from the same grain. Darker malts will produce darker beers.
Nearly all beer includes barley malt as the majority of the starch. This is because its fibrous hull remains attached to the grain during threshing. After malting, barley is milled, which finally removes the hull, breaking it into large pieces. These pieces remain with the grain during the mash, and act as a filter bed during lautering, when sweet wort is separated from insoluble grain material.
Yeasts that ferment at relatively warmer temperatures, usually between 60 and 75 degrees Fahrenheit, form a layer of foam on the surface of the fermenting beer, which is why they are referred to as top-fermenting yeasts (ales). Yeasts that ferment at considerably lower temperatures, around 50 degrees Fahrenheit, have the ability to process a chemical compound known as raffinose, a complex sugar created during fermentation. These yeasts collect at the bottom of the fermenting beer and are therefore referred to as bottom-fermenting yeast. The majority of beer in production today is fermented in this way and is called lager.
Two other types of beer styles include beer of spontaneous fermentation and beers of mixed origin. Beers of spontaneous fermentation are mainly produced in Belgium using wild strains of yeast. These types of beers are often referred to as Lambic. Beers of mixed origin include Altbier and Kölsch.