Several new chemical compounds are formed during this decomposition – mainly oxidised
triglycerides (e.g. acrolein), and coloured compounds. The higher the composition of unsaturated fats,
the lower the smoking point, so the more toxic compounds (like acrolein) are produced on heating to
the same temperature.
Fats being used to fry need to be heated to at least 180 °C. Thus only certain oils are suitable for
frying. Oils that are good for frying include refined oils, such as vegetable oils, which work well
because their smoke points are above 200 °C. Unrefined oils however, such as extra-virgin olive oil,
should not be used for frying because their smoke points are below 180 °C. Equally, frying oil should
not be reused more than three times because the smoke point of any oil will decrease with use.
Heating oil to too high a temperature is also unadvised because at high temperatures, the fat source
may release flammable vapours that cause it to spontaneously ignite.
Role in food
Fats have a very important role in providing flavour. Many molecules responsible for the flavour of
foods are hydrophobic and are thus carried in the fat component of the food.
The presence of fats in food also improves the texture and “mouthfeel” properties of foods.
Fats are also used to cook with instead of water. The advantage of using fat as the cooking liquid
instead of water is that the temperatures that can be reached are much higher than can be reached
when cooking in water, where the maximum temperature reached can only ever be 100 °C, so
reactions that need high temperatures to occur, such as the Maillard reactions responsible for the
colour and tastes of most fried/sauted meats, can occur much more rapidly.
Also, the fats are good conductors of heat. This means that using them will reduce the cooking times
of foods, and this is why vegetables or pieces of meat to be grilled are often oiled first to improve
contact and heat conduction between the frying pan and the meat/vegetable source.
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What should be known about culinary ingredients: Complex carbohydrates