rancid

Rancid, in food science, describes fats and oils that have deteriorated in quality due to lipid oxidation or hydrolysis. It yields off-flavors and odors, often described as stale, cardboardy, greasy, or soapy, and it can accompany texture changes. The term is most commonly used for edible fats and oils rather than for microorganisms-based spoilage.

Rancidity arises from two main processes: oxidation of unsaturated fatty acids (autoxidation) and lipolysis (hydrolytic rancidity). Oxidation forms volatile aldehydes, ketones, and alcohols that give pungent or rancid notes; hydrolysis releases free fatty acids with sour or soapy flavors. Factors include heat, light, oxygen, metal catalysts, and exposure to air.

Signs include off odors, sour or bitter tastes, and a greasy mouthfeel. Oils high in polyunsaturated fats are more prone to rancidity than saturated fats. While rancid foods often taste unpleasant, they are not always unsafe; sensory quality is the primary concern, though some oxidized compounds can be undesirable or harmful in large amounts.

Prevention involves storing fats in cool, dark, airtight conditions; minimizing air exposure; using antioxidants; and observing expiration dates. Proper packaging and rapid consumption after opening also help extend shelf life. If rancidity is suspected, the product should be discarded.

Rancid may also refer to a United States punk rock band formed in 1991 in Berkeley, California. Fronted by Tim Armstrong and featuring Lars Frederiksen, the band fused punk with ska and hardcore and released influential albums such as And Out Come the Wolves (1995).