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Frying Tips

S.A. Fryer Oil Initiative (SAFOI)
Lipid Biotechnology Group
Department of Microbial, Biochemical and Food Biotechnology
University of the Free State
P.O. Box 339, Bloemfontein, 9301.

In South Africa, fried food can be considered a major item in the diet of many people. Consequently, this has resulted in large quantities of frying oil and fat being used and consumed by our community. Attempts to bring about savings in the cost of frying oil has resulted in large quantities of oil being heated repeatedly over long periods and hence becoming severely oxidised (i.e. abused).  As a result, strict regulations have been published in the Government Gazette of 16 August 1996 (No. R1316) which now makes it a criminal offence in S.A. to use edible oils and fats containing more than 25% polar compounds and/or 16% polymerised triglycerides (varnish-like compounds) to fry food with. These products are formed during the extensive use of any type of frying oil and fat and result in the production of poor quality fried food which may be injurious to health.

In this review, tips and a trouble shooting guide will be presented which can be used with great benefit by frying establishments. Most information has been obtained from the excellent publication presented by E.G. Perkens and M.D. Erickson in the book titled Deep Frying: Chemistry, Nutrition, and Practical Applications which was published at the end of 1996.

1.  TIPS

In order to maximise frying oil usage legally as well as obtaining good fried food quality, the following Frying Tips should be adhered to:

Start-up: Always heat frying oil (refers to any type of well refined frying fat and oil collectively) to appropriate temperatures which is usually from 160o to 190oC.  Immediately after reaching this temperature, frying should commence since heating oil earlier than needed will stress the oil and result in unnecessary breakdown which will shorten its usable life-span.

Variable demand: The demand for fried food throughout the production shift should be monitored and taken into account in order to anticipate when fryers should be switched on or off. Keeping oil at high temperatures for extended periods without frying will lead to unnecessary breakdown.

Batch size: The maximum batch size should be set so that the oil temperature in a new batch recovers rapidly to the frying set level reached at the end of the previous frying cycle.

Fryer idling
: It is important that fryers not needed for frying are turned off. Keeping oil temperature any higher than necessary causes breakdown of oil which shortens its useable life.

Crumb control: Crumbs (small pieces of food) in the frying oil will lead to premature oil breakdown which will influence the quality of the fried food. Crumb control can be achieved by separating particles in the food such as chips before entering the fryer and filtering crumbs present in the fryer by skimming off the floating pieces.

Filtration: Filtration of used oil should occur as often as is necessary to prevent crumbs from degrading. Crumb degrading causes dark oil colour, high fatty acid content, scorched and burned flavour leading to a short oil fry-life and poor quality fried food. Frying oil should be filtered once a day when crumb accumulation is minimal, once a frying shift with moderate crumb accumulation and two or more times a shift as needed when crumb accumulation is heavy.

Oil level: During the frying process, let the oil level decrease to a minimum acceptable level towards end of production. This will allow for maximum fresh oil addition and enhanced frying oil quality at the start of the next batch production period.

Fryer shutdown: Turn fryer off immediately after the last batch of food has been fried in order to prevent unnecessary breakdown. This should be followed by oil filtering, cleaning of fryer and covering of fryer to prevent contamination by foreign materials.


The points to follow indicate problems that can be encountered during the frying process. Remedial steps are indicated.



Foaming, which resembles beer foam, occurs when oil degrades due to high temperatures and over-use. This oil should immediately be discarded. The following can contribute to premature foaming:

Salt: Excess salt may be added especially during rush hours resulting in foam formation through soap formation and direct oil breakdown.

Polymerised oil: Broken down oil contains brown gumlike material that accumulates on temperature sensing probes, heating elements of electric fryers, around the perimeter of the fryer at the fill line and on frying baskets causing premature foaming. This material is highly broken down oil resulting from inadequate cleaning and prolonged exposure to high frying temperatures.

Volatile breakdown products: Exhaust fans over fryers allow volatile fat breakdown products liberated from the oil surface to condense on filter screens and on the inside lining the fume hood. If left unattended, condensation could accumulate to a point where these compounds can drip back into the frying oil and cause rapid deterioration.

Boil-out compound residues: It is important to remove polymerised oil from the fryer and should be followed by rinsing with copious amounts of water to remove any residues which may deteriorate oil in use.

Exposure to copper and brass: Inspect thermocouples and frying baskets daily since they may be copper or brass plated with stainless steel and can cause soap formation and hence premature oil breakdown.

Topping up with used oil: Do not use used oil for topping up since this can cause foaming and rapid breakdown of the fresh oil through compounds already in the used oil.

Overheating: Frying at temperatures higher than 200oC causes accelerated oil breakdown which may result in premature foaming and reduced fry-life. Consequently, the temperature of the oil should be measured routinely to verify the accuracy of the thermostat.


Premature smoking:

High amounts of oil breakdown products lead to early smoking of used oil. Smoking of oil is also an indicator of oil degradation and can happen as follows:

Poor filtration and skimming: These result in product remnants remaining in the oil during frying which eventually char and liberate smoke.

Boil-out compound residues: These compounds promote oil breakdown products to form. These oils easily smoke at normal frying temperatures.

Overheating: Too high temperatures cause faster breakdown of frying oil causing premature smoking. This is often caused by a faulty temperature sensing probe or a thermostat which needs recalibration. This should routinely be verified with an adequate thermometer.

Type of product to be fried: If product is coated, “dust” or “powder” may be released into the frying oil causing premature smoking and oil breakdown.


Premature darkening

This may be caused by several factors including:

Inadequate filtration and skimming: When burned remnants are allowed to accumulate in the fryer, it will stain the oil and cause premature darkening.

Overheating: Oil darkening is enhanced due to the formation of oil breakdown products formed at too high oil temperatures.

Improper fryer loading: Make sure the temperature probe is covered by the frying oil. If not, the probe will heat up until the air around the uncovered probe reaches the desired temperature – causing the oil to be burned and to start smoking or even burst into flames.


Bad flavours and odours

“Off” flavours and odours may arise due to the following:

Topping up: When oil is topped up with used oil, the flavours and odours from oil breakdown as well as from food previously fried in the used oil will be carried over.

Improper filtration: Fish fryers and fryers used to fry highly spiced products should always be filtered last to prevent flavour and odour carry-over.

Cross contamination with different frying oils: Different oils have unique flavour profiles and stabilities towards temperature breakdown. Always use one type of oil to minimise “off” flavours and odours.


Oil quality monitoring

Checking oil quality and knowing when to change used frying oil, are critical to maintaining good fried food quality and to operate within the law. For this purpose quality indicators (Test Kits available from various retailers) are used in combination with appropriate thermometers in order to control frying oil temperature during frying.

More information regarding the above can be obtained from Prof. Carlien Pohl-Albertyn

The following reference was used in this study:
E.G. Perkins and M.D. Erickson (1996) Deep Frying: Chemistry, Nutrition and Practical Applications, AOCS Press, Champaign, Illinois. For more information go to