testo 265: Conserving Oil Quality

The quality of the oil will change once operators start frying. That will affect the sensory properties of the food such as its colour and flavour. And bad oil produces bad food.

People have enjoyed fried food for thousands of years, for its great taste, appearance and texture. Hot oil is an excellent heat-transfer medium, so food cooks quickly. Lots of things affect the quality of fried food, especially the type of oil and its chemistry or quality.

The quality of the oil will change once operators start frying. That will affect the sensory properties of the food such as its colour and flavour. And bad oil produces bad food.

Top restaurants have sophisticated procedures to manage the quality of their oil. They know that if just one customer has a bad experience, then sales will suffer. Word-of-mouth can be powerful—it can negate the best-craftedmarketing or advertising campaign.

It’s almost impossible to predict when oil will need changing. There are too many parameters to consider. So frying operators need a tool to make sure they discard used frying oil, and discard it at the proper time. Too early is wasteful. Too late will drive down sales.

Time to take a look at what happens to oil when you cook food. A deep-fat fryer is simply a chamber containing heated oil, into which you put food to be cooked. The speed and efficiency of the frying process depends on the quality of the oil, and its temperature and the quality of oil—typically 140-200°C.

Many other factors affect frying, for example, the time taken and the type of fryer—batch or continuous. The chemical and physical properties of the food are important. So are additives and contaminants, the method of preparation of the food, and the way ingredients interchange with the oil Many chemical reactions take place during frying, that affect the quality and useable life of the oil. Several factors lead to spoilage:

Hydrolysis: This is the major chemical reaction during frying. Water or moisture in the food results in the formation of free fatty acids. The smoked points are reduced and the oil and food develop off-flavours. Baking powder will promote hydrolysis.

Isomerisation or polymerisation: This reaction occurs rapidly during standby and frying periods. The molecule is rearranged and the double bonds can often end up closer together making the fat more unstable and more sensitive to oxidation.

What is %TPM?

The %TPM (percentage of total polar material) measures the extent of thermo-oxidative alteration of a deep-frying fat. According to the 3rd International Symposium for Deep-fat Frying, in Germany March 2000, it’s accepted as one of the best indicators for the rateof oil deterioration/point of discard. It’s internationally recognised.



Changes To Oil During Frying



Pyrolysis: The chemical structure of the fat breaks down into compounds with lower molecular weight.

So how can you tell scientifically when oil is past its best? Many countries have published their own standards for frying fats and oils. Lots of laboratory and statistical works has been done. National regulations often include criteria such as acidity, and levels of polymer concentration or oxidised fatty acids. They may also consider physical values such as viscosity, colour and foaminess. But none of them describe the rate of deterioration exactly.

The most universally accepted standard is the percentage of Total Polar Materials (%TPM). When oil molecules are heated or oxidised they may polymerise—or join together—to form longer molecules with a positive or negative charge on their ends.

Long-term trials suggest that animals fed with large amounts of these polar materials extracted from deep-frying oils and fats may suffer bad health. Effects noticed included slower growth, increased liver and kidney weight, and disorders of the enzyme system. The scientific evidence increasingly backs the view that polarised compounds in oil are detrimental to health and in any case, are nutritionally suspect. Care should be taken that they do not accumulate during frying that goes on for too long, or at too-high oil temperatures.

The German Society of Fat Science (DGF) was a trendsetter in adopting %TPM-analysis when defining basic guidelines for restaurants in the late 1970s.

Since then %TPM-standards have also been adopted by IUPAC (International Union of Pure and Applied Chemistry) and AOAC (Association of Analytical Chemists) International.

As Hazard Analysis Critical Control Point techniques have spread, several European countries have already set limits to the amount of polar compounds in oil at 25 to 27 per cent. Recently, Thailand restricted the maximum %TPM to 25 per cent. Many of its neighbours in Asia and the Pacific region are likely to follow suit.

testo has introduced a portable instrument—the testo 265—for measuring the %TPM that accumulates in deep-fryer fat. It has many advantages. For a start it’s much cheaper than conventional tests in laboratory, and has no running costs. You can put the sensor directly into hot, frying oil and quickly know the quality of the oil and its temperature. It’s easy to clean, thanks to its removable sensor protection cap. And it’s suitable for all kinds of vegetable oils.