Some basic characteristics of oils/fats which need to be taken
2. The potential problems encountered when frying.
3. How each of these problems can be minimised/controlled.
4. Other considerations that need to be taken into account when
choosing which frying medium to use
1. Some basic characteristics of oils and fats
and fats are made up of mixtures of triglycerides and each triglyceride
is made up of three fatty acids that are attached to a glycerol
When a glycerol molecule and three fatty acid molecules are
brought together the product is a Triglyceride and water, unfortunately
this reaction is a reversible reaction and thus a Triglyceride
will breakdown to produce free fatty acids when it comes into
contact with water - This is the first important point to note.
In addition the fatty acids themselves are of differing types
both in chain length but more importantly in terms of degree
of saturation. The levels of un-saturation are described in
terms of Saturated, Monounsaturated, and Di or Tri-unsaturated
saturated fatty acid has no areas of weakness and is thus classed
as very stable
monounsaturated fatty acid as its name suggests (mono = one)
has one area of weakness and thus only has relative stability
Di and tri unsaturated fatty acids as their name suggests (di
= two and tri = three) have two or three areas of weakness and
are thus classed as unstable.
is these areas of weakness along the fatty acid molecule that
make that particular fatty acid susceptible to reaction with
oxygen -This is the second important point to note.
when edible oils and fats are subjected to the frying process
they are very susceptible to both.
Oxidative breakdown via reaction with Oxygen
Hydrolytic breakdown via reaction with water.
addition the frying process is carried out at elevated temperatures
which itself leads to Thermal breakdown.
need to be aware that during the frying process all three of
these forms of oil degradation are taking place at the same
time and so we need to take positive steps to minimise their
effect, see section 3 below.
2. Potential problems encountered when frying.
During the frying process oils and fats have to combat an array
of attack from various sources.
Oxygen ( Fryer open to contact with the air)
2. High Temperatures ( Heat required for frying the food)
3. Water ( The food is usually wet when it is fried)
Dirt ( Particulate matter, namely frying debris)
5. Light ( Fryer open to contact with light )
6. Soaps ( Left over from cleaning)
7. Trace metals ( Equipment/utensils contain oxidative catalysts
such as copper, iron or brass)
from these sources will lead to the following Physical/ Chemical
OR FAT DARKENS IN COLOUR
FATTY ACID LEVELS
These aforementioned observations during the breakdown will
with time lead to poor odours and tastes not only in the oil
but more importantly in the finished fried product.
Free fatty acid level, colour level, smoke point and flash point
can all be measured analytically, however, in the small frying
trade it is the visual signs that are used to monitor the quality
of the oil.
Note: with time the free fatty acid level and colour increases
in value while the smoke and flash points decrease in value.
These increases and decreases are closely related to each other
comes a point during the frying process when all these parameters
start to accelerate and it is at this point that the oil starts
to break down very rapidly
There is a period of reasonable Free Fatty
Acid stability beyond which the oil will begin to degrade
free fatty acids are used in many technical applications because
of their “wetting properties” it is this effect that one observes
when one sees a higher then normal absorption of oil into the
final fried product and so obviously the higher the percentage
absorption into the finished product the greater the bearing
the oil has on finished product quality.
raised levels of Fatty Acids are also in direct relationship
with the increased frothing and increased smoking. Not only
do we see a reduction in product quality but we also increase
the risk of either environmental problems through excessive
odours or at the worst the risk of a fire. This then leads us
into the area of risk reduction and the positive steps we need
to take to minimise oil breakdown.
3. Minimising the effect of oil breakdown.
issues involved in oil breakdown are fairly complex and all
efforts should be made to reduce the “loading Effect” against
the oil. As the oil is subject to extreme conditions it will
inevitably lead to deterioration, the control of which can either
extend or reduce the lifetime of the oil.
consider each of the factors.
Frying Temperature and effective control of such.
temperature control is essential, the frying of chips should
be done between 170 and 180 C and the frying of fish should
be done between 175 and 185 C. These frying ranges are best
maintained by the use of a thermostat and it is always good
practice to check the accuracy of the thermostat from time to
time by the use of a dip thermometer.
at too high a temperature will result in food that is darkly
coloured plus the breakdown process of the oil will proceed
much faster (For every 10C rise in temperature above the recommended
frying temperature of 180C the thermal stability of the oil
will be halved.
at too low a temperature will result in food being too greasy
through excessive absorption of the oil.
the key here is for proper and effective heat control –
use an accurate and well maintained thermostat. It is
also recommended that an automatic safety cut out is installed
to ensure the oil is kept well below its flash point and thus
reduces the risk of fire.
b. Correct preparation of raw materials in particular moisture
think it is fair to say that fish poses very few problems with
regard to moisture levels as it is usually left to defrost into
drip trays thus leaving very little free moisture on the product.
The main cause of oil breakdown thus comes from excessive moisture
on the chips.
or other potato products are usually prepared well in advance
of cooking and in some cases potatoes will have a tendency to
discolour if left for any period of time untreated, thus there
are several products on the market which can be employed to
stop this discolouration.
These products ensure that the potatoes can be well drained
of moisture and stand for much longer periods of time without
the key here is to ensure the potatoes are well washed after
chipping ( to remove all the free starch that has been released)
all chips are evenly treated and all treated potatoes are well
drained prior to cooking.
These steps prevent excess starch and/or moisture making contact
with the oil, which will help reduce the speed of oil breakdown.
c. Particulate production and its efficient removal
main causes of particulate production are, batter scraps, from
the frying of battered fish and other food particles mainly
starches from potatoes which are insoluble in the oil.
reason particulates are a problem is because they create a large
surface area for the oil to react upon, plus the particulates
themselves can accumulate, become charred and cause additional
breakdown products as well as aid oil polymerisation.
is always good practice to continue to sieve out the batter
scraps after each and every frying,
however the very minute black specs which can pass through a
fairly fine sieve need a much more efficient system for removal
and this involves a more sophisticated filtration system.
the pans used for frying should be filtered on a daily basis.
In most cases the cleaning system involves removing the hot
oil from the pan, cleaning the pan by the removal of any built
up brown resinous material and then filtering the oil through
a very fine mesh back into the clean pan. Once a week a more
thorough clean should be carried out, when the pan is empty
it should be given a scrubbing with hot water and detergent.
Care must be taken at this point to ensure that all detergent
used is thoroughly rinsed away and the frier is completely dry
before putting back the oil.
the key here is to have a daily filtration
regime which will remove any free particles and
a scheduled deep clean which will remove products of
d. Minimising contact with air and light.
the section on characteristics of the oil/fat we encountered
the idea of un-saturation. The degree of un-saturation is related
to the relative stability of the oil, so the more unsaturated
the oil/fat has, the more areas of weakness it has and consequently
the more unstable it is.
When the oil comes into contact with light and air it gives
rise to an Oxidation reaction ( as it reacts with the oxygen
in the air) which forms decomposition products. These products
are formed due to the breakdown at the weakest point and they
give rise to “off odours” and poor flavours, they also contribute
to lowering the smoke and flash point of the oil.
minimise the effect of light and air the frying range covers
should be closed when the fryer is not being used.
Minimising contact with soaps.
is recommended that the frier is deep cleaned on a regular basis
using a soap or detergent. Care must be taken to ensure that
all traces of soap/detergent are thoroughly rinsed away as both
soap and alkaline detergents generally promote the breakdown
minimise the effect of soaps always thoroughly rinse and dry
the pan before adding fresh oil.
f. Minimising the effect of trace metals ( copper, Iron,
metals such as Copper and Iron have a catalytic effect on the
oil breakdown i.e they increase the speed at which the breakdown
occurs. For this reason you should ensure that all utensils,
fixtures and fittings are made from stainless steel. In addition
it is recommended that salt is not added to the food prior to
frying as the sodium ions from the salt (Sodium Chloride ) also
catalyse the oxidation reactions.
key here is to only use stainless steel utensils, fixtures and
Some other considerations
factor that will reduce the increase in breakdown of the oil
is that of oil turnover, if the oil is constantly been used
up by absorption into the finished product then the pan will
need constant topping up with fresh oil. This in turn will keep
the oil reasonably fresh and if the rate of replacement is high
enough the discarding of oil may not be necessary.
b. Oils containing synthetic Antioxidants and Anti-forming agents
vegetable oils contain a level of natural antioxidants, however,
these levels are reduced by some of the processing steps carried
out by the manufacturer. In order to prolong the shelf life
of the packaged product the manufacturer can add synthetic antioxidants
to the oil, which is denoted by an E number declaration. Unfortunately
their effect is only very minimal, as heat and steam (in the
frier) combine to break them down and volatilise them.
Anti-foaming agents can also be added by the manufacturer, these
products which are silicone based form a mono layer on the surface
of the oil and this helps to reduce oxygen ingress.
oil has its own stability profile, however, the manufacturer
has at his disposal some means of improving the stability of
a less stable liquid oil. The method the manufacturer will use
is called Hydrogenation, this process in effect changes the
oils characteristics by removing one or more areas of weakness
and in doing so the liquid oil becomes more solid. The benefit
of this is a medium with a longer life but on the down side
the hydrogenated product is more costly and contains a much
higher level of “Trans Fatty Acids”.
have carried out tests to measure the stability of different
types of oil and fat. From the results a table of an oils/ fats
stability can be drawn up – see below
Hydrogenated Fats = Most Stable
Rapeseed oil = Least Stable
The type of oil used in the fish and chip trade is very dependent
upon the region in which it is used and customer preference
a good tasting product, well presented and packaged at a fair
price will go a long way to ensuring customers make repeat visits.
this document we have covered the main factors involved in the
frying process. We have looked at some basic oil and fat chemistry
and the role`s heat and oxygen play in oil breakdown.
We also looked at other factors that contribute to oil breakdown
and how these can be minimised and controlled.
we looked at some other considerations which need to be taken
into account when choosing the correct frying medium, customer
preference and geographical region being the most important.
In the final summary it must be said that the life of a frying
oil is under the control of the frier and the process he/ she
subjects it to with regard to heat, moisture, air, frying debris,
light, trace metals and soaps.
ten commandments of good oil management can be found on the
• ENSURE FRYING TEMPERATURES ARE UNDER EFFECTIVE CONTROL
• SIEVE OUT BATTER SCRAPS CONTINUOUSLY DURING FRYING
• FILTER DAILY USING AN EFFICIENT SYSTEM
• MELT DOWN SOLID FATS AT LOWER TEMPERATURES (120 C)
• ENSURE RAW MATERIALS ARE WELL DRAINED AND FREE OF EXCESS MOISTURE
• CHECK THE FUME EXTRACTION SYSTEM FOR OIL BUILD UP ON A REGULAR
• MINIMISE LIGHT AND AIR INGRESS
• EMPTY AND DEEP CLEAN THE FRIER ON A REGULAR BASIS
• TOP UP WITH FRESH OIL ON A REGULAR BASIS
• DO NOT USE COPPER, IRON OR BRASS UTENSILS IN THE OIL