Nut rancidity is the oxidative or hydrolytic deterioration of unsaturated fats in kernels, producing off-flavours and odours that render product unfit for sale and are detected by peroxide value and free fatty acid testing.
In trade practice
Buyers specify maximum peroxide value and free fatty acid limits in purchase contracts, and accredited laboratories test samples at origin and at intake. Elevated peroxide value indicates active oxidation, while high free fatty acidity often points to earlier lipase activity linked to poor drying or mechanical damage. Nitrogen flushing and barrier packaging slow oxidation during transit, but rancidity that has already developed cannot be reversed by packaging alone.
In a specification
A specification should state maximum peroxide value and free fatty acid limits by test method, the sampling point at which they apply and the shelf life remaining at delivery.