If you break beer down it is simply fermented, hop flavoured, malt sugared, liquid. The basic ingredients of beer are water, malt, hops, and yeast. The major variation in beer is the type of yeast used to ferment the product.
Water comprises more than 90% of beer. Almost any water can be chemically adjusted to create the exact style of beer desired, although pure water supplies are still prized greatly.
Barley is a basic cereal grain not particularly good for milling into flour and making bread or bakery goods. But it is great for beer. There are three major types of barley. The number of seeds at the top of the stalk differentiates these. Barley seeds grow in two, four and six rows along the central stem. European brewers traditionally prefer the two-row barley because it malts best and has a higher starch/husk ratio than four or six-row barley. Brewers in the US traditionally prefer six-row barley because it is more economical to grow and has a higher concentration of enzymes needed to convert the starch in the grain into sugar and other fermentables.
The barley must then be malted before being used to brew beer. Malting is a process of bringing grain to its highest point of possible soluble starch content by allowing it to sprout roots and take the first step to becoming a normal, photosynthesising plant. It is at this point that the seed is rich in the starch it needs to use as food for growth. Then, the maltster heats the grain to a temperature that stops the growth process but allows a natural enzyme, diastase, (which converts starch into sugar or maltose) to remain active. The roasted malted barley no longer has the active enzymes needed to turn the starch into sugars, but does impart characteristics that add flavour to the beer. The degree of roasting determines the colour of the beer and the greatest roasted malted barley will impart its roasted flavour to the beer.
Hops are a flowering vine whose flowers are used as a preservative and for their essential oils that add flavour (bittering hops) and aroma (aroma hops) to balance the sweetness of the malt. Usually dried before use, the bitter flavour of the hop is extracted during the boil. The aroma is provided by aroma hops whose essential oils provide the aroma.
Yeast is unicellular fungus. It is the most essential, yet least understood aspect of brewing beer.
The yeast are there to convert the sugars in the wort into alcohol. Yeast that adds little in the way of flavors are usually described as having a “clean taste”. Yeast produce three metabolic by-products that affect beer taste: phenols – spicy or clove like taste or medicinal taste; esters – a fruity taste; Diacetyls – a butterscotch or “woody” taste. The presence of any of these flavour components depends largely on the style of beer being brewed. Much depends on individual palates and the effect the brewer is aiming for.
Some beer styles are “spiced” with ingredients such as coriander, Curacao, all-spice and others.
Adjuncts, other ingredients such as rice or corn, can be used to “extend” the ingredients imparting a “clean” to “no taste” and providing the beer with longer shelf life.