Beer is the world's most widely consumed and probably the oldest alcoholic beverage. The production of beer involves the processing of starches mainly derived from cereals or in some cases derived from other plants, adding a natural yeast to produce the fermentation and a flavourings such as hops or others.
This is a generic description for all kind of beer, but there are so many variables to produce thousands of different beers.
Beer is composed mostly of water, about 90% of the finished product. The big breweries treat the water before processing to have a standard product.
The second critical element is the cereal for the fermentation.
You can produce beer with any type of cereal, wheat, corn, rice or others although the main one is barley.
In some countries for reasons of oppotunity other plants are used so there are beers of agave or potato in South America and beer of cassava root in Africa among others. Unprocessed cereals may not ferment. They generally must be transformed into malt. Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air. Malting grains develops the enzymes required for modifying the grain's starches into sugars fermentable.
Different roasting times and temperatures are used to produce different colours of malt from the same grain. Darker malts will produce darker beers.
Barley is the most commonly malted grain, in part because of its high diastatic power or enzyme content, though wheat, rye, oats and rice are also used.
Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolises the sugars extracted from grains, which produces alcohol and carbon dioxide, and thereby turns wort into beer. In addition to fermenting the beer, yeast influences the character and flavour.
The dominant types of yeast used to make beer are the top-fermenting and bottom-fermenting.
The strength of beer is usually around 4% to 7% alcohol by volume (abv), although it may vary between 0.5% and 20%.
Flavouring beer is the sole major commercial use of hops. The flower of the hop vine is used as a flavouring and preservative agent in nearly all beer made today. The flowers themselves are often called "hops". Before that hops became main flavouring, beer was flavoured with other plants for instance, grains of paradise or alehoof. Combinations of various aromatic herbs, berries, and even ingredients like wormwood would be combined into a mixture known as gruit and used as hops are now used. Some beers today use plants other than hops for flavouring. 

KNOW THE BEER

Basic knowledge
Basic knowledge
Basic knowledge