Tips and troubleshooting guides that frying establishments can significantly use. Most information was obtained from the excellent publication by E.G. Perkens and M.D. Erickson, in the book Deep Frying: Chemistry, Nutrition, and Practical Applications published at the end of 1996.

Frying Tips

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 well-refined frying fat and oil collectively) to appropriate temperatures, 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 an unnecessary breakdown which will shorten its usable lifespan.

Variable demand: The demand for fried food throughout the production shift should be monitored and considered to anticipate when fryers should be switched on or off. Keeping oil at high temperatures for extended periods without frying will lead to an 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: Fryers not needed for frying must be turned off. Keeping oil temperature higher than necessary causes oil breakdown, shortening its useable life.

Crumb control: Crumbs (small pieces of food) in the frying oil will lead to premature oil breakdown, influencing 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, and 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 twice or more in 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 the 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 the fryer off immediately after the last batch of food has been fried to prevent unnecessary breakdown. This should be followed by oil filtering, cleaning, and covering the fryer to prevent contamination by foreign materials.

Trouble Shooting Guide

Remedial steps are indicated for problems that can be encountered during the frying process.


Foaming resembles beer foam 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 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 the inside lining of 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: Removing polymerised oil from the fryer is crucial. It should be followed by rinsing with copious amounts of water to remove any residues that may deteriorate oil 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 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, resulting in premature foaming and reduced fry-life. Consequently, the temperature of the oil should be measured routinely to verify the thermostat's accuracy.

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 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 quickly 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 a good thermometer.

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

Premature darkening:

Several factors may cause this:

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 at too high oil temperatures.

Improper fryer loading: Make sure the frying oil covers the temperature probe. If not, the probe will heat up until the air around the uncovered probe reaches the desired temperature, causing the oil to burn and start smoking or bursting 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 and 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 is critical for quality fried foods and abiding within the law. For this purpose, quality indicators (Test Kits available from various retailers) are used with appropriate thermometers to control frying oil temperature during frying.

E.G. Perkins and M.D. Erickson (1996) Deep Frying: Chemistry, Nutrition and Practical Applications, AOCS Press, Champaign, Illinois. 

For more information:

Prof Carlien Pohl-Albertyn

Prof Carlien Pohl-Albertyn


Elfrieda van den Berg (Marketing Manager)
T: +27 51 401 2531


Dilahlwane Mohono (Faculty Officer)
T: +27 58 718 5284

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