Topics In This Section
1. Introduction
2. General Rules of Frying
3. Temperature Control
4. Preparation of Food
5. Fat Absorption and Topping Up
6. Choice of Frying Medium
7. The Spoilage of Fats and Oils
8. Cleaning
9. Frying Specific Foods
10. Recommended Frying Temperatures
11. The Basic Chemistry of Fats and Oils
12. The Chemistry of Fat Spoilage
13. The Visible Effects of Chemical Spoilage
14. The Role of the Oil Refiner
15. The Role of the Fryer
16. Fire Hazards
Reproduced with permission from Pura Food Products Limited
9 Frying Specific Foods
Doughnuts
It has already been mentioned that the fat absorption of potato chips is of the order of 5-6%. Doughnuts absorb much more fat during frying: figures above 30% have
been recorded and it has been said that the fat used for frying doughnuts discolours and smokes more readily than fat used for frying potato chips. However, because
of the higher rate of absorption, the frying medium is 'turned over' at a greater rate. It is necessary to be particularly careful when frying doughnuts. For example,
it is preferable to rest or prove the doughnuts on greased, rather than floured, surfaces because the flour will tend to fall off into the frying fat and char.
Some of the factors influencing the amount of fat absorption have already been mentioned in Section 5. One of the reasons doughnuts have a higher absorption rate that
chips is the more porous nature of the doughnuts' surface, but other points are of interest, In chemically raised doughnuts, it appears that increased fat and increased
sugar in the recipe both result in more fat being absorbed during frying. The greater the surface area, the greater the absorption; cracks and rough surfaces increase the
area, and finger shapes and rings have more surface area than spheres. There is also evidence that fat absorption is decreased by warmer ingredients, longer mixing times
and stronger flours, although each of these may also result in poorer eating qualities. It is also advisable to experiment before adopting a new method.
Unless automatic equipment is being used, it is not easy to handle fully proved pieces of dough without damaging the structure. The dough can be transferred to the fryer
by means of an oiled palette knife and the finger tips. Yeast raised doughnuts should be placed in the frying medium upside-down; this avoids the instability of the doughnuts
during the second half of the frying process, after they have been turned over.
Many types of doughnuts are sugared after frying. For this reason, it is preferable to use a solid fat, because sugar adhesion is better and the sugar does not discolour
so readily. The flavour of the doughnuts can be improved by adding a small quantity of cinnamon or mixed spice to the sugar. The doughnuts should be allowed to cool before
sugaring, to prevent the formation of a wet, sodden coating caused by the steam escaping from the doughnut during cooling, The sugar in which doughnuts are rolled will pick
up a quantity of fat; in bakeries, this sugar should be kept separate because some confectionary products, notably meringues, will suffer if fatty sugar is used.
Frozen Fish
When frying frozen fish, the main point to bear in mind is that the sudden immersion of very cold material into a frying oil is likely to reduce the temperature considerably.
The effect of this will depend on the type of frying equipment used. In automatically controlled fast recovery kettles, the temperature of the oils will return quickly to the
correct point while the food is being fried. In slower kettles and ones which are controlled by hand, the frying temperatures may not recover in time and allowances must
therefore be made when setting the temperature of the oil before the food is introduced.
Above 191C (375F) the oil will spoil rapidly and if fish is fried at too high a temperature, the batter will cook too quickly and too hard, while the fish at the centre may
remain relatively uncooked. If the temperature is too low (because of the effect of the frozen fish), fat absorption will be greater and the food will be soft and greasy.
Frozen Food Generally
The points made in the section on frozen fish are true of frozen foods in general. As well as these, it must be remembered that free ice is often present in foodstuffs which
have been frozen. This ice becomes water and produces steam during frying and there is therefore the danger of introducing excess moisture into the frying kettle with the food,
Also, thick pieces of frozen food are difficult to cook right through, and they considerably reduce the temperature of the frying medium. As long as the food is small or in thin
sections, this may not be a problem, but larger pieces benefit from thawing before frying. In this case, it is preferable to drain the defrosted food to remove excess moisture
produced by the melting ice. Defrosted foods should be handled carefully, because they are often fragile.
Potatoes
Potatoes should be stored in a cool, 7-10C (45-50F) dark, dry, airy place and not in close proximity to strong smelling produce or products.
The varieties which are most widely used are the second earlies Estima and Wilja and maincrops such as Desiree, Maris Piper, Pentland Crown, Pentland Dell and Pentland Squire,
Medium to large tubers tend to give a higher yield of long chips and many buyers therefore purchase supplies graded over a 45mm or 50mm square riddle. Potatoes with a low dry
matter content tend to produce soggy chips. Processors test samples with a potato hydrometer and will not usually use samples with dry matters below 19%. If the tubers have
been stored at below 7-10C (45-50F) or are immature, the reducing sugar content may be too high (over 0.25%). Such samples produce dark brown chips. Samples can be test fried
before purchase to eliminate those samples with excess sugar or which produce chips that turn black after cooking.
After peeling and chipping, the pieces should be kept soaking in water until required, to remove surface starch and to retard the development of discolouration or browning.
Several proprietary potato 'whiteners' are available and these prevent discolouration; when used, the manufacturer's directions should be carefully followed. Too strong a solution,
too long an immersion period or insufficient draining can result in a discolouration of the frying medium. In some cases, excess free starch on the potato is transferred to the
frying medium where it will carbonise and cause the medium to deteriorate more rapidly.
Deep fried potatoes can be cooked by 'straight through methods or by blanching and browning in two stages.
In the 'straight through' method, raw potato chips are deep fried at 188-191C (370-375F) until brown and cooked, (4-5 minutes). These can be stored for short periods
in a warm dry place.
In the blanching and browning method, the potato chips are first blanched by frying at 168-177C (330-350F) until cooked but not brown (4-6 minutes). After draining, these can be
stored, but should be refrigerated if kept for more than two hours. When required, blanched chips are browned by frying at 191C (375F) (2-3 minutes). The advantage of this
two-stage method is that much of the cooking process can be completed during slack periods.
Vegetables and Fruit
Firm vegetables (cauliflower, carrot, onion) can be cut of separated into uniform pieces and fried at 177-191C (350-375F). Before frying the pieces are dusted with flour and
dipped in batter, or soaked in milk or beaten egg and dipped in breadcrumbs or seasoned flour. Frying times will vary according to size but is generally between 2-4 minutes.
Softer vegetables (corn etc) can be mixed with a batter and spooned into the frying medium.
Fruit is generally dipped in fritter (that is, sweetened) batter and fried at 177-188C (350-370F) for 2-4 minutes depending on size and type. Pineapple, bananas, peach, apple
slices etc can be treated in this manner.
Foods containing fat
Precautions should be taken against contaminating the frying medium with other fats. Sausages, chicken, beefburgers and other meat products all contain carious amounts of fat
which is still in its natural unrefined state. Obviously these will tend to melt during the frying process and their presence will lessen the life of the frying medium.
Enclosing such food in batter before frying will tend to reduce this danger.