Many kinds of beer are made using just four ingredients: malted barley, hops, water, and yeast. These beers still exhibit a wide range of flavors and styles due to variability in these four ingredients. Variation in brewing technique also plays a role in producing interesing beer flavors.


See main article on grains and sugars. See list of grains and sugars.

Malted barley is the principal source of fermentable sugars for beer. Malting is the process of partially germinating the grains of barley to increase their fermentable sugars. During normal germination and malting chemical reactions take place inside of the grains that mobilizes energy stored as starch by breaking it down into simple sugars which can be used directly to fuel the growing plant. Simple sugars also fuel yeast growth in fermentation. Maltsers next arrest germination by kilning or toasting the grains. Numerous different types of malt are produced with different degrees of toasting and other properties. Basic pale-colored malt produces lots of fermentable sugars with mild flavor. Crystal malts have undergone a stewing step during malting that convers some portion of thier sugars into non-fermenting sugars. A kilning step after the stewing causes caramelization. Crystal malts add mouthfeel and caramel flavor and leave some residual sweetness. Dark roasted malts are toasted at very high temperatures. These add flavors similar to coffee and dark chocolate. More exotic malts have been created to among other things maximize malt aroma, add smoke flavors, and acidify the mash without using brewing salts.


See main article on hops. See list of hop varieties.

Hops are the flowering cones of a climbing vine. Hop cones are rich in flavorful and aromatic plant oils. Brewing with hops infuses these flavor producing compounds into the beer. Many different varieties of hop plant exist with different agricultural properties and different balances of flavor compounds, such that each variety has a unique flavor profile. Several hop breeding programs continually seek to produce new varieties with good flavors and crop yeilds. Hop bitterness is the flavor of primary interest. Bitterness is mostly determined by the concentration of compounds known as alpha-acids which convert into bitter compounds the longer they are boiled. Additional hop flavors are commonly described using the terms spicy, floral, fruity, herbal, and earthy. These flavors and aromas are produced by volatile essential oils.


See main article on water.

Groundwater is not just pure H2O. It starts out as relatively pure rain water, but as it seeps into the ground many minerals and ions from the surrounding geology become dissolved in it. The ion content in groundwater from wells at different locations can vary substaintially. Ions affect many steps of the brewing process from the pH of mashed grains, growth and health of yeast, and finally human perceptions of flavor. It is theorized that beers styles from certain locations evolved to complement the properties of the groundwater available.


See main article on yeast. See list of yeast strains.

Yeast produce alcohol and carbon dioxide as waste products from fermentation of sugars. Breaking down sugars produces energy for the yeast cells to grow and divide. Along with alcohol and carbon dioxide yeast produce other flavorful fermentation by products. Different strains of yeast and different fermentation conditions particularly temperature cause different yeast outcomes. The flavors produced by yeast can be dramatic and vary greatly between different strains of yeast. Well known fermentation by products are: esters (pear-like, banana-like, spicy, or oaky), fusel alcohols (solvent-like), acetaldehyde (green apple), diacetyl (butterscotch), and phenols (medicinal or clove-like).


Great effort is usually taken to favor fermentation by yeast instead of bacteria. This is the reason for sanitation and for boiling the wort. However in some styles the peculiar flavors imparted by bacterial fermentation are traditional and desirable.

Other Grains

Some beers make use of grains other than barley. Nearly always these grains augment rather than replace barley as a source of sugars. Wheat is a popular choice as it contributes a mild but desirable flavor. Oats and rye are essential ingredients in certain styles because of their distinctive character. Other grains such as corn and rice are more often used as adjuncts to reduce the body of the beer without contributing much flavor of their own.

Kettle Sugars

Kettle sugars are refined sugars added directly to the boil. These could technically include malted grain extracts (dried malt extract and liquid malt extract) but more commonly refer to sugars from non-grain sources like sugar cane, sugar beets, and honey.