Topics In This Section
1. Introduction
2. General Rules of Frying
3. Temperature Control
4. Preparation of Food
5. Fat Absorption and Topping Up
6. Choice of Frying Medium
7. The Spoilage of Fats and Oils
8. Cleaning
9. Frying Specific Foods
10. Recommended Frying Temperatures
11. The Basic Chemistry of Fats and Oils
12. The Chemistry of Fat Spoilage
13. The Visible Effects of Chemical Spoilage
14. The Role of the Oil Refiner
15. The Role of the Fryer
16. Fire Hazards
Reproduced with permission from Pura Food Products Limited
14 The Role of the Oil Refiner
The oil refiner can do a number of things to help damp down the chemical spoilage of a frying oil or fat.
Oils have different stabilities towards heat and frying, and these differences are due to their basic chemistry. In particular these differences are related to the number
of points of weakness in the molecule. Some oils and fats are stable enough for many food applications, but are too sensitive to heat to merit consideration for use as a frying
medium. The refiner will know from experience which oils, and which blend of oils are likely to give better performance than others. Those which find commonest use include palm,
soyabean, sunflower and rapeseed oils, lard and tallow or dripping; also available are corn, groundnut and cottonseed oils, but these are generally more expensive.
It is more important to properly refine a frying fat or oil than any other. If all the impurities naturally present in the crude oil are not removed in the refining process,
they can cause all these spoilage reactions to go on at a faster rate. Naturally occurring emulsifiers such as lecithin, which is found in most crude oils, will cause a frying
medium to smoke or discolour sooner. Small quantities of metal elements such as copper and iron are fatal because they will provoke the reaction known as oxidation. Special
efforts are made by the refiner to remove these metals and in normal circumstances, one would expect to find less that one part of them in about one million parts of refined oil.
This care can be completely cancelled out by the fryer by using equipment containing, say copper or brass.
The refiner can use additives to improve the stability of his oil. Antioxidants, for example are permitted additives which slow down the rate of oxidation. This effect is most
marked in the storage period, when it delays the onset of spoilage by oxidation. Once the oil is heated to frying temperature, this effect tends to be lost because the antioxidant
is eventually boiled off.
The refiner can also add substances known as antifoaming agents. These tend to reduce the amount of frothing or foaming which takes place at the surface of the fat and by doing
this, they cut down the rate of deterioration, particularly that caused by oxidation. Because antifoaming agents are extremely effective, the average rate of addition is as low
as two parts per million.
It is also possible to improve the stability of an oil or fat by chemical modification. In section 11, there appeared a number of diagrams which illustrated the shape of fat
molecules. Most of them had 'points of weakness' in them to greater or lesser extents. In general, the more points of weakness there are, particularly if they are close together,
the less stable the oil will be towards heating and the less stable it will be towards frying. That is because (see Section 12), the spoilage reaction known as oxidation can occur
at these points of weakness.
It is possible to use a chemical process to reduce the number of points of weakness in a fat or oil
This process is called hydrogenation and it is achieved by bubbling gas called hydrogen through the heated oil under very carefully controlled conditions. It results in the
gradual disappearance of these points of weakness and because of this, the oil becomes more stable. The melting point of the oil is increase at the same time, and because of
this, the process is often called 'hardening'.
Physical modification of oils is also possible, and it can take several forms. For example, it is possible to take fat which is normally solid at room temperature , melt it
and allow it to cool slowly in a tank so that it begins to crystalise. After allowing this to occur, it can be filtered to give a liquid portion and solid portion. Palm Oil
can be subjected to this process and the liquid part which is obtained can be used as frying oil.
To summarise, an oil refiner can use a number of techniques in order to produce a frying medium, of good performance:
Choice of oil - Proper refining - Use of additives - Chemical modification - Physical modification.