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 discared. The following can contribute to premature foaming:
Excess salt may be added especially during rush hours resulting in foam formation through soap formation and direct oil breakdown.
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.
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.
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.
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.
Do not use used oil for topping up since this can cause foaming and rapid breakdown of the fresh oil though compound already in the used oil.
Frying at temperatures higher than 200˚C 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.
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:
These result in product remnants remaining in the oil during frying which eventually char and liberate smoke.
These compounds promote oil breakdown products to form. These oils easily smoke at normal frying temperatures.
Too high temperatures cause faster breakdown of frying oil causing premature smoking. This is often caused by a faulty temperature sensing probe of a thermostat which needs recalibration. This should routinely be verified with an adequate thermometer.
If product is coated, “dust” or “powder” may be released into the frying oil causing premature smoking and oil breakdown.
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.
Oil darkening is enhanced due to the formation of oil breakdown products formed at too high oil temperatures.
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.
“Off” flavours and odours may arise due to the following:
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.
Fish fryers and fryers used to fry highly spiced products should always be filtered last to prevent flavour and odour carry-over.
Different oils have unique flavour profiles and stabilities towards temperature breakdown. Always use one type of oil to minimise “off” flavours and odours.
Checking oil quality and knowing when to change used frying oil, are critical to maintaining good fried food quality and to operate withing the law. For this purpose quality indicaters (Test Kids available from CH OIL TRADERS) are used in combination with appropriate thermometers in order to control fryinig oil tempreature during frying.