Frying seems like a simple culinary practice, although in reality an entire art is hidden behind this apparently simple process. In this culinary process there are certain rules that we must follow if we want to taste those crispy golden potatoes or battered fish. In addition to choosing the best oil to do it with, which is very hot (although it does not exceed 180 °C) and that we change it regularly, there is another lesser-known aspect that we must also pay attention to.
We are talking about the mixture of oils, a problem that may have gone unnoticed by us. However, who hasn’t mixed two different oils because a little was left at the bottom of the bottle and they had to open a new one of a different type of oil? A common practice that is better to leave aside because, among other things, during frying the oil undergoes a series of changes that are different depending on the type of product we are using.
Oils, temperature and unwanted substances
Sunflower, olive, rapeseed, coconut, virgin olive… The variety of oils that we can find is very interesting and each of them has its own particularities and different uses. Olive oil, for example, is one of the most used and valued, not only because it is rich in vitamins and omega 9, but because it is an oil that resists temperature variations very well, although it is important not to exceed its smoke point, that is, from when it begins to deteriorate and form polar compoundschemical substances that result from the decomposition of oil and that are the result of factors such as the action of heat, light, oxygen and water in the products that are fried.
The smoke point of an oil is a marker that tells us when decomposition begins to occur and refers to the temperature at which a fat or cooking oil begins to break down into glycerol and free fatty acids.
In the industrial field, specifically in catering companies, bars and restaurants and other companies dedicated to the preparation of pre-cooked dishes, the Quality Standard for Heated Oils and Fats contemplates a condition for these polar compounds and that is that their presence must not overcome, under no circumstances, 25%.
So, at home, can we mix olive oil, for example, with sunflower oil (which is cheaper) for frying? As we have already advanced, if we do so, we will be making a big mistake. The problem is that each oil has a different smoke point, that is, olive oil has a higher smoke point than sunflower oil. Therefore, negative compounds begin to form in the latter before they do so in the olive oil. And this is causing the olive oil to spoil more easily.
The changes that occur in an oil when we fry are the result of the oxidation of the triglyceride component with the formation of peroxides, free fatty acids and polymers. And its appearance basically depends on the temperature reached, the time we use it – the number of times we reuse it – and the composition of each type of oil. Different types of oil have different fatty acid contents, which largely determine their thermal stability. For example, oils with a high degree of unsaturation are the least suitable for frying because they do not hold up as well to prolonged and repeated heat treatments.
What happens with mixtures of reused olive oil with new one?
Another case that we can find in the kitchen when using oil for frying is to use one that we have already used (we must keep in mind that we can use an olive oil between three and four times) with another that is the same, but ‘new’. , that is, what we use for the first time. In this case, we can mix them, but taking into account that the one that indicates the number of times we can use it again is the old one, not the new one that we just added.
In this case, we must pay attention to the alteration of flavor and the appearance of these polar compounds, whose presence is higher the higher the temperature and the more uses we are giving to that oil.
We will notice that an oil has been used too much because physical-chemical changes occur, such as the appearance of a more intense color, greater viscosity, as well as a greater probability of foaming because the smoke point decreases.
Other recommendations to keep in mind when frying
We have already seen that frying can be a challenge if we do not use oils well. But, in addition to what has been mentioned, there are other recommendations that we should not ignore:
- Prioritize extra virgin olive oil: if we talk in terms of health, the extra virgin olive oil is best suited for frying and, although its smoke point is around 200 °C, that is, it begins to smoke and degrades sooner, if this temperature is controlled it is the most suitable.
- Maintain a temperature below 200 °C, around 180 °C: at this temperature we not only prevent the formation of polar compounds, but we also prevent the food from absorbing less oil. At lower temperatures, foods may become soft. And, at temperatures that are too high, the exterior burns before the interior is cooked, causing an unpleasant taste and a potential food safety issue. If we don’t have a kitchen thermometer on hand to check the temperature, one way to know if the oil is ready is to throw a small piece of bread; If bubbles form around it, it means it is. This trick works for both virgin olive oil and sunflower oil.
- Fry little by little: the ingredients have to be added little by little into the oil so that the temperature does not drop. In this way we can cook at an adequate and invariable temperature.
- Drain well: at the same time as removing the food from the oil, we must put it on a kitchen paper so that it absorbs all the fat.
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