Deep-Frying Oil: How Long Does It Last?

There are many factors that determine how many times you can reuse deep-frying oil. The type of oil, the food being fried, the temperature, and the method of filtration all play a part. For example, oils with a high smoke point, such as canola, sunflower, and vegetable oils, are better suited to high temperatures and can be reused more often. The food being fried also makes a difference, with non-breaded foods allowing for more reuse than breaded foods. To increase the lifespan of your oil, it is recommended to filter or strain it after each use, store it in an airtight container, and avoid overheating it. While there is no definitive answer to how many times you can reuse deep-frying oil, it is important to regularly check for signs of spoilage, such as a dark colour, a rancid smell, or foaming, and to prioritise your health by replacing the oil when necessary.

Oil type and temperature are key factors

Oil Type

Different oils have different smoke points, which determine how hot they can get before burning. Oils with higher smoke points are better for deep frying as they won't burn or produce off-flavours. Oils with high smoke points include canola, sunflower, and vegetable oils. Peanut oil and avocado oil are also suitable for deep frying but will impart a distinct flavour to the food.

Oil Temperature

Deep frying requires high temperatures. Food needs to be fried at high temperatures to achieve the perfect crunch and crispiness. However, oil that is heated at extremely high temperatures can become rancid and develop an unpleasant taste and odour. Oil heated at high temperatures also becomes dark in colour and thick in consistency, indicating signs of rancidity.

To prevent oil from becoming rancid, it is important to maintain the right temperature during the frying process. The normal temperature range for food service frying is 325 to 375 °F. However, higher temperatures of 375 to 400 °F can also be used. Most foods cook rapidly in the 325 to 375 °F range and develop a golden colour, crisp texture, and good flavour. Frying at lower temperatures results in lighter colour, less flavour development, and increased oil absorption, while high-temperature frying leads to thinner crusts and less oil absorption.

It is also important to note that the temperature of the oil drops when food is added to the fryer. The temperature drop can be higher for frozen foods. To ensure proper cooking, the temperature of the oil should recover to its set point by the end of the frying cycle. Oil oxidizes faster at higher temperatures, so choosing the right frying temperature is crucial.

Reusing Oil

It is possible to reuse cooking oil, but it should not be reused more than two or three times due to potential bacteria growth from leftover food particles. To extend the life of the oil, strain out any bits of food after each use and store it in a sealed and light-proof container. Used frying oil can be stored for up to 3 months, and it is recommended to refrigerate it to ensure the best quality.

Additionally, it is important to change the oil regularly to maintain taste and protect your health. For example, if you frequently fry breaded foods, change the oil after 2 to 4 uses as the high temperature can cause the oil to go rancid. For non-breaded food, the oil can be reused 6 to 8 times.

The type of food being fried matters

Battered foods like onion rings or bare foods like french fries will leave behind very little detritus after frying. Breaded foods like chicken cutlets will leave crumbs that fall off when added to the oil. Foods dredged in flour will introduce a lot of particles. So, while oil used for battered foods may last through a dozen or more batches, oil used for flour-dredged foods may break down after only three to four uses.

With battered and breaded foods, what's inside doesn't matter as much as it doesn't come into direct contact with the oil. But for foods that are fried bare, the type of food can affect the overall quality of the oil. Vegetables tend to fry the cleanest, imparting very little to the oil. On the other hand, fatty meats like chicken wings or bacon will render fat as they cook, and this fat can mix with the fryer oil, causing it to break down a little faster.

The frying vessel impacts oil lifespan

Therefore, if you are frying at home, you may want to consider purchasing a dedicated electric deep fryer. This will help to prolong the life of your oil.

Another factor that will affect the lifespan of your oil is the type of food you are frying. Battered foods, such as onion rings, will leave very little detritus after frying. Breaded foods, such as chicken cutlets, will leave crumbs in the oil. Foods dredged in flour will introduce a lot of particles. Oil used for battered foods may last through a dozen batches, while oil used for flour-dredged foods may break down after three to four uses.

The type of food being fried also makes a difference. Vegetables tend to fry the cleanest, imparting very little to the oil. Fatty meats, such as chicken wings or bacon, will render fat as they cook, and this can mix with the fryer oil, causing it to break down faster.

Oil freshness affects its hydrophobic nature

Oil is hydrophobic, meaning it repels water. This is because oil and water do not mix, and oil does not easily absorb water. This property is what makes deep frying so effective. When a piece of food is submerged in hot oil, the water within it vaporises and escapes as bubbles.

However, the hydrophobic nature of oil is affected by its freshness. Fresh oil is highly hydrophobic, and will not absorb much water. But as oil degrades, it becomes less and less hydrophobic. This breakdown is caused by the oil being reheated, as well as exposure to humidity, light, and heat during storage.

Interestingly, this degradation can actually be advantageous for deep frying. Less hydrophobic molecules in the oil allow it to come into closer contact with food, improving the efficiency of frying. This is why some chefs, particularly those specialising in tempura, add a small amount of degraded, old oil to a new batch.

But as the breakdown continues, the oil will eventually lose its hydrophobic properties, and start to enter the food too rapidly. This will cause the food to become greasy and lose its crispness. At this stage, the oil needs to be replaced. Signs of old oil include foam on the surface, an inability to reach frying temperatures without smoking, a dark colour, and a musty or fishy smell.

Filtering and storing oil correctly prolongs its life

Deep-frying oil can be reused many times, but there are several factors that determine how long it lasts. These include the type of oil, the food being fried, the frying temperature, and how often the oil is filtered.

Filtering

Filtering the oil after each use helps to remove small food particles, which can cause the oil to break down more quickly. To filter oil, allow it to cool to room temperature, then carefully filter it through a sieve or strainer lined with muslin, kitchen paper, paper towels, or a coffee filter.

Storing

Oil should be stored in an airtight container in a cool, dry, and dark place. Never pour hot oil into a container, and always store used oil separately from new oil.

Other tips

• Avoid cooking foods at temperatures above 375°Fahrenheit (190°C).
• Salt foods after deep frying.
• Keep your deep fryer clean.
• Refrigerate stored oil.

Frequently asked questions