Beer is made from four basic ingredients: water, barley, hops, and yeast. The type of water used can affect the taste of the beer, so brewers often use water that is high in minerals. Barley is the main source of starch in beer, and it is what gives beer its body and colour. Hops are flowers that add bitterness and aroma to beer. Yeast is the microorganism that ferments the sugar in the barley into alcohol.