Most beer begins with four ingredients: malted grain, hops, yeast and water. Their proportions matter, but their varieties, chemistry and treatment matter just as much.
Malt: fermentable extract, colour and body
Malting allows grain to germinate under controlled conditions and then dries it in a kiln. Base malt supplies most fermentable sugar and enzymes. Crystal, caramel and roasted malts add colour and flavours from bread crust and caramel to coffee and cocoa.
Hops: bitterness, flavour and aroma
Boiling converts hop alpha acids into bitter iso-alpha acids. Later additions preserve more volatile oils, while dry hopping extracts aroma after fermentation. Variety and harvest quality can produce herbal, floral, citrus, resinous or tropical profiles.
Yeast: alcohol and fermentation character
Yeast converts fermentable sugars mainly into ethanol and carbon dioxide. It also creates esters, phenols, sulphur compounds and other flavour-active molecules. Strain health, pitching rate, oxygen and temperature shape the result.
Water: the quiet structural ingredient
Calcium, magnesium, bicarbonate, chloride and sulphate affect mash pH, yeast performance and flavour balance. Brewers adjust water for process needs and style, but more minerals are not automatically better.