The oxidation stability characterizes the resistance of oils and fats as well as fat-containing foods to oxidation and is thus an estimate of how quickly a fat or oil will become rancid. The 743 Rancimat is the most widely used instrument for the determination of the oxidation stability and allowing the simultaneous testing of up to eight samples in accordance with international standards. More details about the Rancimat method are provided by a technical poster.

In the Rancimat method, a stream of purified air passes through the fat-containing sample, which is held at a specified temperature in a thermostatted aluminium block. The effluent air from the oil or fat sample is then bubbled through a vessel containing deionized water. The conductivity of the water is continually monitored and stored by the software on the attached PC. The end of the induction period corresponds to the appearance of the secondary oxidation products – volatile organic acids, predominantly formic acid – which are blown out of the sample and absorbed in the water. At that time the conductivity begins to increase rapidly.

A number of fat-containing solid foodstuffs such as almonds, peanuts, peanut flips, potato chips, biscuits, butter cookies, french fries and instant noodles were successfully tested with the Rancimat method.

For most food samples, powdering is recommended, because the more homogeneous the sample, the better (steeper) the obtained measuring curve. In cases where the sample cannot be powdered the crushed sample should be homogenous with a maximum particle size of approximately 5 mm.