Deep frying: all you need to know
I really feel like publishing sensantional titles: ‘Deep frying, no panic!’ ‘Deep frying, all you need to know to healthy deep fry’… I even dare to use an infinitive split :D
OK, just kidding. But we must admit that, in these times of healthy food paranoia, deep frying hasn’t seen many fans. Many recipes that were conceived as deep fried (donuts, krapfen, tortillas…) present now an oven baked version. I tried to keep an open mind and tested a few oven baked alternatives, and I must say they have a few advantages over the deep fried versions. First of all, baking is less messy (and safer as there’s no oil spraying around). Secondly, oven baked alternatives are lighter, as you do not need all the oil you use to deep fry. Despite that, although an oven baked donut is yummy, it can’t compare with the deep fried version, selon moi :)
Now, I have the theory that eating some deep fried food, once in a while (e.g. 1-2 times a month), can’t hurt (I herein invite some nutritionist to share his/her opinion :)). And given that deep fried recipes were not one of my strengths, I researched and practiced to master the technique.
Here the main rules (and reasons) for a proper deep frying:
Type of oil and “smoking point”
The oil selection is the starting point for properly deep frying. Contrary to what Italians think, olive oil is not the best choice :)
Oil should be selected based on its “smoking point”. What is the smoking point? It is the temperature at which the fats of the oil start to decompose and form acrolein, a toxic compound. You realize that because the oil gets smoky and has an acrid smell. WHO recommends to do not exceed the daily oral acroilen intake of 7.5 ug/kg body weight.
For such a reason, oils with a high smoking point are more stable and preferable for deep frying. Oils containing a higher amount of polyunsaturated fats are more “fragile”, because the unsaturation (the double bond on the molecule) is a point of instability.
Here the smoking points for a few common frying fats:
Peanut oil: 220 C
Lard: 188 C
Olive oil: 175 C
Sunflower seed oil: 170 C
As you can see, lard and peanut oil have a higher smoking point than olive oil. Bare in mind that the composition of fatty acids may vary even for oils of the same type. Therefore, smoking points can change.
Personally, I deep fry in sunflower oil that has a neutral taste. I prefer to use olive oil to dress or stir fry. Furthermore, olive oil, as well as peanut oil, leaves a pronounced aftertaste. With that said, using olive oil for deep frying is still OK, as the smoking point is relatively high.
Temperature of the oil
When a food is immersed in hot oil, the water contained evaporates quickly (from here the bubbles you see). That leads to the formation of an external crust, generated by the coagulation of proteins.
Thus, which temperature is the right temperature? It depends on the type of oil. With peanut oil you can reach 170 C, but with the sunflower one we need to stay around 150-160 C. In any case, it is recommended to do not go above 180 C, as you risk to have a food burnt outside and raw inside. If the temperature is too low, the water evaporates slowly and the crust take a while to form. Consequently, food starts to absorb oil.
A cooking thermometer, meant for high temperatures, helps with monitoring the oil temperature. Deep frying machines are excellent, because they maintain a constant oil temperature.
Use a lot of oil (2-2.5 inches in height) and deep fry one piece at the time. When food is immersed into the hot oil, the oil temperature goes down. If you use a large amount of oil, introducing one piece at the time will only slightly alter the temperature.
Container
Despite frying pans are logically associated to deep frying, I prefer to use tall and narrow pots. This minimize the surface of oil exposed to air and prevents an excessive oxidation of the fats.
Salting
Salt enhances the oxidation of the fatty acids. Therefore, it is recommended to salt the food after and not before deep frying.
Is it possible to recycle the oil used?
Theoretically yes, provided that you didn’t overheat the oil (you should have not reached the smoking point) and you filter the oil (after having left it cooling down). Anyway, the oil should not be recycle too many times, also because it can compromise the taste of the food.
Personally, I never recycle the oil used, I rather prefer to start with a new batch each time I deep fry.
References
L. Di Carlo, Tradizione in Evoluzione, Chiriotti Editori, 740-744.
K. Abraham, S. Andres, R. Palavinskas, K. Berg, K.E. Appel, A. Lampen, Toxicology and risk assessment of acrolein in food, Mol. Nutr. Food Res., 2011, 55, 1277–1290
L.R. Mariutti, N. Bragagnolo, Influence of salt on lipid oxidation in meat and seafood products: A review, Food Res. Int., 2017, 94, 90-100