The main ingredients found in beer are water, malted barley, hops, and yeast. There are other ingredients such as flavoring, sugar, and other ingredients that are commonly used. Starches are used as well, as they convert in the mashing process to easily fermentable sugars that will help to increase the alcohol content of beer while adding body and flavor.

Water

Seeing as how beer is mainly composed of water, the source of water and its characteristics have a very important effect on the character of the beer. A lot of beer styles were influenced by the characteristics of water in the region. Although the effect of minerals in brewing water is complex, hard water is more suited to dark styles, while soft ware is more suited to light styles.

Malt

Among malts, barley is the most widely used due to its high amylase content, and a digestive enzyme that facilitates the breakdown of starch into sugars. Depending on what can be cultivated locally, other malts and unmalted grains can be used, such as wheat, rice, oats, and rye.

Malt is obtained by soaking grain in water, allowing it to germinate, then drying the germinated grain in a kiln. By malting the grain, enzymes will eventually convert the starches in the grain into fermentable sugars.

Hops

Since the seventeenth century, hops have been commonly used as a bittering agent in beer. Hops help to contribute a bitterness that will balance the sweetness of the malts. They also contribute aromas which range from citrus to herbal.

Hops also provide an antibiotic effect that favors the activity of brewer's yeast over the less desirable microorganisms. The bitterness in beer is normally measured on the International Bitterness Units scale.

Yeast

Yeast is a microorganism that's responsible for fermentation. Specific strains of yeast are chosen depending on the type of beer produced, as the two main strains are ale yeast and lager yeast, with other variations available as well.

Yeast helps to metabolise the sugars that are extracted from the grains, and produces alcohol and carbon dioxide as a result. Before the functions of yeast were understood, all fermentations were done using wild or airborne yeasts.

Clarifying agent

A lot of brewers prefer to add one or more clarifying agents to beer that aren't required to be published as ingredients. Examples include Isinglas finings, which are obtained from swim bladders of fish and Irish moss, which is a type of red alga.

Since these ingredients can be obtained from animals, those who are concerned with either the use or consumption of animal products should obtain detailed information from the brewer.