Does Deep Fryer Oil Go Bad? Understanding Oil Lifespan

Deep-frying at home can be messy, costly, and dangerous. But if you're using a lot of oil, you'll want to get the most out of it. So, can you reuse deep fryer oil, and if so, how many times?

The good news is that you can reuse frying oil, but there are some rules to follow. Firstly, start with a good frying oil that has a high smoking point (400°+), like peanut oil, canola oil, or vegetable oil. Then, carefully maintain the oil's temperature as you fry – if oil surpasses its smoke point, its fats start to break down, releasing a substance called acrolein, which gives food a bitter taste.

Once you've finished frying, let the oil cool, then filter it through a cheesecloth or coffee filter to remove any crumbs or sediment. Store the oil in an airtight container in the refrigerator.

Each time you reuse oil, it becomes more destabilized until it decomposes. Used oil can give food an acrid aroma, and if it looks cloudy or foamy, it's time to toss it. Even if the oil looks and smells fine, it's recommended to reuse frying oil no more than three times before discarding it, and definitely not after one to two months.

It's also important to note that frying oil will take on the flavour of the food you cooked in it, so don't use the same oil for, say, fish and doughnuts.

Reheating oil can be harmful to health, causing inflammation, high cholesterol, and acidity

Reusing deep fryer oil can be harmful to your health. While it may be tempting to reuse oil to save time and money, doing so can lead to a range of negative health consequences. Reheating oil can increase levels of inflammation in the body, which is the root cause of most diseases, including obesity, heart disease, and diabetes. High levels of inflammation can also reduce immunity and make you more prone to infections.

Reusing cooking oil can also lead to higher levels of LDL, or "bad," cholesterol in the body. This, in turn, increases the risk of heart disease, stroke, and chest pain. Additionally, reheated oil can cause a burning sensation in the stomach and throat and contribute to acidity.

The dangers of reheated oil lie in the chemical reactions that occur during the heating process. These reactions produce harmful byproducts such as aldehydes, which are toxic elements, and free radicals, which can cause inflammation and oxidative stress in the body. Reheating oil can also affect serum lipid profiles, blood pressure, and promote atherosclerosis, osteoporosis, and liver and kidney inflammation.

To avoid the negative health impacts of reheated oil, it is recommended to cook food in fresh oil for each meal and in small quantities to avoid waste. Home-cooked meals are ideal as they give you control over the ingredients used and can provide a balanced diet. When eating out, opt for foods that use less oil, such as salads, or carry your own home-cooked meals.

Oil lifespan depends on type, use, and maintenance

Type of Oil

Oils with a high smoke point (400°F and above) are best for deep frying. Examples include peanut oil, canola oil, sunflower oil, and vegetable oil. Oils with low smoke points, such as extra virgin olive oil, are not suitable for deep frying.

Use

The number of times oil can be reused depends on what is being fried. Breaded foods, such as poultry, meat, and crumbly foods, require more frequent oil changes (after 2 to 4 uses). For non-breaded foods, such as french fries and other vegetables, the oil can be reused 6 to 8 times.

Additionally, the type of food fried will impart its flavour onto the oil. For example, oil used for frying fish will likely be unsuitable for frying doughnuts next.

Maintenance

To prolong the lifespan of oil, it is important to strain or filter it after each use to remove any impurities, crumbs, or sediment. Oil should be stored in an airtight container in a cool, dark place between uses. Temperature control is also crucial; heating oil above its smoke point will cause its fats to break down, leading to a bitter taste.

Oil takes on the flavour of the food cooked in it

Oil can be reused several times, but it's important to know when to discard it. Each time you reuse oil, it becomes more and more destabilised until it decomposes. When oil is heated, its molecules join together to form much larger molecules, giving the oil a thick, gummy consistency and a darker colour.

The flavour of the oil is also something to consider when reusing it. Oil takes on the flavour of the food cooked in it, so it's best to label used oils with what they were used for to prevent any unfortunate flavour overlaps. For example, you wouldn't want to use oil that was used for frying fish to make doughnuts.

To prolong the life of your oil, temperature control is key. Oil has a specific smoking point, which is the temperature at which the oil starts to smoke. When oil surpasses its smoke point, its fats start to break down, releasing a substance called acrolein, which gives burnt food its bitter taste. Frying with old oil will cause any type of food to taste acrid and greasy.

To prevent oil from going rancid, it's important to store it properly. Oils degrade in response to heat, light, and oxygen, so it's best to store them in a cool, dry place and in an airtight container.

Oil can be reused, but only after it has cooled

To filter the oil, drape a few layers of cheesecloth or coffee filters in a fine-mesh strainer or chinois over your storage container. Pour the oil through the cheesecloth or coffee filters to catch any crumbs. Storing the oil in an airtight container in the refrigerator is ideal.

It's also important to label the container with the date, what the oil was used for, and the number of times it has been used. Then, store the oil in a cool, dark place until you're ready to reuse it.

It's worth noting that frying oil will take on the flavour of the food you cooked in it. So, if you used the oil to fry fish, it's probably not a good idea to use it for doughnuts next. However, you can go in reverse—for example, using oil that was used for doughnuts to fry something savoury.

Oil should be strained and stored in a cool, dark place

Oil should always be strained and stored in a cool, dark place. This is because frying oil can take on the flavour of whatever it was used to fry. For example, if you use oil to fry fish, it will likely not be suitable to fry doughnuts next. However, frying something savoury in oil first is fine if you plan to use the oil for something sweet later.

To reuse frying oil, you need to strain it and store it in a lidded container in a cool, dark place. Once you have finished frying, let the oil cool completely in the frying vessel. Once it has cooled, strain it into a clean vessel, such as a glass jar or the container it came in. It is helpful to use a funnel for this.

It is also a good idea to label the container with the date, what the oil was used for, and the number of times it has been used.

Frequently asked questions