When assessing the state of frying oils and establishing when they should be discarded, there are many criteria, laws and different analytical techniques (refraction value, grade of acidity, peroxide value, iodine value, polar compounds, dielectric constant, etc.).
The laws of most of the European countries establish that the parameter to take into account is the percentage of polar compounds which must not equal or exceed a value in the range of 24-27%, depending on the country. Polar compounds are a group of alteration compounds, harmful to consumer health and formed during the deep-frying process where there are free fatty acids, monoacylglycerides, diacylglicerides, oxidized triacylglycerides, secondary compounds of oxidation, oxidized dimers and polymers, etc.
This quality standard applies to natural and legal people whose activities include the use and manipulation of heated edible oils and fats to manufacture food products: catering, street food vendors, bars, fast food restaurants, and all types of tourist establishments, both permanent and temporary facilities, and those set up in public areas during parades or events with heavy concentrations of people (fairs, etc.).
The technique of the official method to measure polar compounds, chromatography on silica column, is complex, requires several hours, and must be developed by specialized laboratories.