comprise a chemically diverse group of organic compounds, the common and defining feature of which is their solubility in organic solvents and their insolubility in water. There are differing methods of lipid classification taking into account polarity, functional groups, and complexity. Lipids include a broad range of molecules such as “fatty acids”: terpenoid lipids (sterols, carotenoids, etc.), tocopherols, glycerides, phospholipids, waxes, oils, and others.

Lipids comprise 2.2%–2.5% of the dry substance of barley, predominantly located in the aleurone layer (60%) and in the germ (30%). Of these, the majority are triglycerides used by the seedling during germination and growth. Therefore, after malting, total lipids are reduced by approximately 25%.

Lipids are present in yeast and comprise 2%–12% of the dry matter of yeast cells. Yeast lipids (mostly phospholipids and sterols) are found along with proteins in the cell membranes, and lipid synthesis is an important part of yeast reproduction. However, lipids ought not to be present in finished beer, where they can cause staling problems and negatively affect foam stability. Brewers will generally avoid the production of cloudy worts, which tend to have high lipid levels.

Lipids negatively affect foam stability as well as aging stability.