Anisidine Value (AnV): AnV is measured by reacting the oil with a solution of p-anisidine in acetic acid, and measuring the increase in absorbance of light at a specific wavelength (350 nm).
Bleaching: The oil is mixed with a carefully measured quantity of diatomaceous earth, which absorbs the colour components from the oil. The process is a gentle one, and does not involve the use of chemical bleach, as is sometimes supposed! This process also removes metal ions, any residual chlorophyll and other components that may adversely affect the stability of the oil.
Cold Test: This test determines whether the oil remains clear and bright when subjected to low temperatures.
Colour Index: The colour of the oil is measured using a yellow/red scale specially developed for oils and fats by the American Oil Chemists Society. The measurement is performed on a dedicated colour comparison machine (Lovibond). The Gardner colour scale is another measurement of colour that is generally accepted and widely used by the industry.
Degumming: Gums (phosphatides), plus any chlorophyll and destabilising metal ions, are removed by washing the oil with high purity water and food-grade phosphoric acid.
Deodorizing: The strong flavour and aroma of the oil is removed by heating the oil under high vacuum. All volatile components are driven off, including most oxidation products, leaving the oil virtually odourless.
Fatty Acid Composition: The oil is separated into its component fatty acids on a capillary column in a gas chromatograph, and the relative contents measured. Note that the fatty acid contents are conventionally expressed as the percentages of the total fatty acids. The oil will also contain other components, such as the glycerol backbone from the triglycerides, and the non-saponifiable fraction. These fractions must be taken into account if the weight of a given fatty acid per gram of oil is to be calculated.
Filtering: The crude oil produced by cold pressing is often cloudy because it contains fragments of seed material. These fragments are removed by filtration to leave a clear, bright oil.
Heavy Metals: Measurement of possible toxic contaminants such as lead, mercury and cadmium.
Iodine Value: A measure of the degree of unsaturation of the oil. This measurement has been largely superseded by the fatty acid profile, which gives a more accurate indication of oil quality, but it is still used on occasion (most commonly by skincare formulators).
Neutralisation: The oil is treated with an alkali solution that neutralises any free fatty acids, which can then be removed, along with any lecithin and phospholipids.
Organoleptic Testing: This is a fancy term for taste and smell, which are of course very important for many applications.
Acid Value (AV): Measures the degree to which the triglycerides in the oil have broken down to release free fatty acids, by measuring the amount of alkali needed to neutralize a sample of oil.
Peroxide Value (PV): PV is measured by titration with a solution of potassium iodide.
Saponification Value: Measures the number of milligrams of potassium hydroxide needed to neutralise all the fatty acid molecules (both free and in triglycerides) in 1g of oil. It is an indication of the mean molecular weight of the fatty acids in the oil.
Unsaponifiable Matter (USM): Measures the percentage of the oil by weight that is not present in the form of triglycerides or fatty acids. This will include sterols, tocopherols, carotenoids and pigments.
Winterization: Seed oils naturally contain varying amounts of waxes and gums. These compounds can cause the appearance of haze or sediments in oils during their shelf life, which is unacceptable, particularly in clear-encapsulated products. Winterization involves holding the oil at a low temperature to encourage these components to crystallize, whereupon they can be removed by a final filtration.