Fatty Acids, a subcategory of lipids, comprises a range of related organic chemicals that includes fats, oils, and waxes. Their physical properties are largely determined by the length and degree of unsaturation of the hydrocarbon fraction of their molecular structures. The nonpolar hydrocarbon chain accounts for the poor solubility of fatty acids in water while the carboxylic acid group is polar and accounts for the higher solubilities of short-chain fatty acids in water. Butyric acid, for example, with only four carbon atoms is readily soluble in water. The simplest lipids constructed from fatty acids are triglycerides, better known as fats.
Fatty acids are relevant in brewing because they negatively affect the organoleptic stability of beer during aging. The breakdown of unsaturated fatty acids such as linoleic and linolenic acids into staling compounds such as (E)-2-nonenal, known for its typical “cardboard flavor,” is well documented.