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Everyone loves deep-fried food and the best fried food is cooked in good oil. Cooking oil degrades with high heat, time and exposure to air, and water that is in the food. Looking after the oil in your deep fryer will give better results on the plate and better profits in the kitchen.

Getting the temperature right is essential to looking after your oil. If you’re going through a lot of oil, the temperature could be set too low, or the thermostat is not working properly. At the right temperature, the hot oil causes the food to start forming a crust in 60 seconds, stopping further penetration of the oil into the food. But if the oil is not hot enough, the crust won’t form as quickly and more oil will be absorbed by the food. When oil reaches its smoking point – the temperature when it starts to break down and form bitter compounds – this actually lowers the smoking point. So, the idea is to fry under the oil’s smoke point. Most of the time, we’re frying between 170°C and 185°C. But the longer you cook with oil, the lower its smoke point becomes.

Smoke points

  • Safflower oil 266°C
  • Soybean oil 257°C
  • Olive oil 242°C
  • Palm oil 232°C
  • Corn oil 232°C
  • Peanut oil 232°C
  • Sunflower oil 227°C
  • Extra virgin olive oil 207°C
  • Canola oil 204°C


Starch floating about the oil is a problem for several reasons. It causes foaming and the oil to spill over and, because it is so fine, it needs to be filtered from the oil. Reduce the amount of starch in your oil by ensuring that potatoes, for instance, are soaked to remove starch and thoroughly drained. Frozen French fries are made from potato varieties with ideal starch levels. Dusting food in flour so it won’t stick together before frying can be a problem as it continues to fry and make bitter compounds. Consider separating foods using kitchen paper instead.

Orderly fashion

If you’re frying large amounts of different foods in prep, for example, consider the order in which you approach the job. Vegetables have the lowest effect on oil so cook them first. Foods covered in batter factor in next as batter sticks to food, and any little blobs that float off can quickly be removed with a steel skimmer. Food that is crumbed is not great for cooking oil. The crumbs float off and are difficult to remove except by filtering the oil. They continue to cook, darken and produce those bitter compounds and degrade the oil.


Water is oil’s enemy. It makes oil foam and does not allow it to cook food properly. Moisture from food also causes the oil to hydrolyse and shorten its useful life. Watery foods such as chicken wings can be par-baked to start cooking and remove moisture, then finished to order in the deep fryer. Buying par-fried French fries reduces the amount of moisture getting into the oil. Ensure all utensils are bone dry and the fryers are properly dried after cleaning. Look out for condensation dripping back down into the oil from the extraction fans.


Salt – Another enemy of your oil is salt. It gets into the oil and speeds up chemical changes. Don’t season food before it goes into the deep fryer. Copper and brass also change the chemistry of oil.

Follow the instructions that come with your oil, skim it regularly during service, filter it, turn off the fryers as soon as practical, top it up regularly and change it regularly. Invest in the best oil you can, as cheap cooking oil will break down faster than good oil. Happy frying!

As seen in summer 22/23

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