The fries are a real delicacy. But also a health hazard, because they put a strain on the stability of the oil. Recently, new research carried out by the University of Illinois and published in Cancer Prevention Research confirms that reusing frying oil is bad for your health.
So, how often should fryer oil be changed?
The researchers’ discovery establishes that when frying oil is used repeatedly, very dangerous genetic changes can occur in the body. This can increase the production of cancer cells. The deleterious action also affects metastases and changes in lipid metabolism. Definitely healthier is steam cooking.
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Is reusing cooking oil bad for your health?
This detrimental effect occurs because repeatedly used frying oil produces a highly toxic chemical called acrolein. This molecule is responsible for serious health problems. Including carcinogenic proliferation, atherosclerosis and the development of heart disease.
Acrolein is formed during the heating process of frying oil, by the oxidation of triglycerides, which are composed of fatty acids and glycerin.
When we heat oil to high temperatures, exposure to oxygen in the air and the presence of food can trigger a degradation process, which oxidizes the oil. It also causes the detachment of glycerin from fatty acids and forms acrolein.
This harmful substance separates from the oil at a certain temperature, called the smoke point. In fact, it is the thermal value at which the production of a toxic and very irritating smoke occurs. Both for the eyes and the respiratory tract.
This explains why many cooks have an increased risk of developing respiratory diseases and eye disorders.
Oxidation occurs faster at higher temperatures. Furthermore, prolonged and repeated use can significantly degrade the oil.
Therefore, the oil in a fryer must be changed completely and periodically. And it must not be mixed with the new one.
What oils to use for frying?
Type of oil recommended for frying:
So which is the ideal oil for frying? At the top of the ranking, undisputed, we find olive oil, which has a reduced content of fatty acids and the high natural concentration of anti-oxidants allows it to protect itself from temperatures and preserve its properties. However, this oil is rarely used, especially by restaurateurs, due to its high cost.
Excellent choices can be soybean oil and corn oil (which are rich in monounsaturated fats which give them great oxidative stability), or peanut oil, which contains a very low amount of polyunsaturated fatty acids (35%), and sunflower oil (55%).
The optimum temperature for frying is around 180°C. At lower temperatures, the food becomes soaked in oil.
While at higher temperatures it risks burning quickly. And it’s important that the oil you choose has a smoke point higher than the frying temperature.
Can the restaurateur reuse the frying oil?
Since reusing frying oil can be bad for your health, restaurateurs must comply with precise obligations and legal limits in the event of reusing frying oil. If there is a violation, they risk severe penalties.
The degree of danger of the oil already used for frying is due to the presence of certain substances, called polar constituents, which increase according to the degree of degradation of the oil.
These substances are given by the transformation of the fatty acids contained in the oil, which thus becomes potentially carcinogenic.
Polar substances, if present in large quantities, i.e. over 25%, slow down the cooking process and crust formation. Thus fried food will contain unhealthy oil and carcinogenic substances.
Each type of oil behaves differently, but some studies show that already from the second or third use for frying the safety level of 25% is exceeded.
How to reuse frying oils in a safe way for health?
- Only use oils and fats suitable for this use for frying.
- Do not let the oil exceed the temperature of 180°C. For this reason, it is mandatory to use fryers equipped with a thermostat.
- Frequently replace the oil used for frying. The oil that is no longer usable can be recognized by its browning, viscosity and excessive smoke production during cooking.
- Filter used oil before reuse.
- Do not use top-up. That is, never mix new oil and oil that has already been used for frying.
- Protect oils and fats from light.
When to change the frying oil?
Do not reuse oil that contains more than 25 grams of polar constituents for every 100 grams of oil.
To avoid exceeding the legal limit, experts recommend changing the fryer oil or using tools to check the content of polar compounds.
It is the responsibility of the catering operators to preserve the characteristics of the foods without altering the organoleptic characteristics: the oil must be changed whenever it appears darkened or viscous.
Other general rules for respecting the health of customers:
- Thoroughly dry the food and avoid using spices to avoid accelerating the degradation of the oil
- Never exceed the temperature of 180°C
- At the end of service, if the oil is still usable, filter it to eliminate frying residues
- Never add fresh oil to used oil
- Do not expose oils to sunlight
Different types of oil, different replacement times
To identify the right time to change the oil, a distinction must also be made based on the type of oil used:
- Palm oil: product with the highest smoke point, it keeps its characteristics unchanged up to a temperature of 240°C.
- Peanut oil: particularly suitable for superficial frying and frying baths, it does not alter the taste of the food to be fried. It has a smoke point of 210°C.
- Soybean oil: it is ideal for frying fatty elements; in fact, with this type of oil there is no risk of decomposition of the fatty matter. The sore point is that it tends to go rancid. Smoke point at 190°C.
- Seed oils (such as sunflower or corn): if unrefined they are not suitable for frying. They have a very low smoke point ranging from 130° to 160°C.
The correct frying oil temperature and smoke point
By the smoke point, we mean the temperature at which the oil begins to oxidize following the separation of the glycerine from the fatty acids. This process creates acrolein, a substance highly harmful to the gastric tract and hepatotoxic even at low concentrations.
For correct frying, the oil temperature must be between 165° and 185°C, therefore it is necessary to use an oil that can withstand this temperature range without degrading.
How to store used oil correctly
The tips below will help you store your fryer oil safely and effectively for reuse.
- oil container or glass jar with lid
How to store used oil:
- Check the label on your cooking oil container to see if the manufacturer has included any storage recommendations for your particular type and brand of oil. Although most edible oils are generally stored the same way, some may have more specific storage requirements or a longer shelf life than others.
- Allow the deep fryer oil to cool to about room temperature after you turn off the heat.
- Drain the oil through cheesecloth in order to remove the bacteria so that you can safely reuse the oil.
- Pour the oil strained into a glass jar with a metal lid or back into its original packaging if possible.
- Tightly seal the container and store it in a cool, dark, dry place at room temperature or in the refrigerator if you live in a very hot climate. While the oil may appear a little cloudy after some time in the refrigerator, it should become clear again once it reaches room temperature.
Final Word: How often should fryer oil be changed?
In conclusion, the research conducted by the University of Illinois confirms the health risks associated with reusing frying oil. Not only does repeated use of frying oil increases the production of cancer cells, but it also affects metastases and changes in lipid metabolism. Thus, it is strongly recommended that frying oil should be changed regularly in order to reduce the risk of health issues. In addition, steam cooking is considered to be a healthier alternative to fried foods.