Storing Used Deep Fryer Oil: How Long Is Too Long?

How long your deep fryer oil lasts depends on several factors, including the type of oil, what you're frying, and how well you've strained it. If you're reusing oil, it's best to store it in a sealed container in a cool, dark place. Oil can be strained and reused several times, but it's important to pay attention to any changes in colour, smell, or taste, as this may indicate that the oil has gone bad.

Storing used deep fryer oil

Straining and Cooling the Oil:

Start by allowing the oil to cool completely in the deep fryer or frying pan. It is important to let the oil cool down to room temperature before handling it. Once cooled, carefully strain the oil to remove any food particles, batter, or breadcrumbs. These residues can accelerate the degradation process, so it's best to remove them. You can use a cheesecloth set in a fine-mesh strainer or a simple strainer by itself. Some people also use disposable coffee filters or a handkerchief-lined funnel to strain the oil effectively.

Storing the Oil:

Used deep fryer oil should be stored in a clean, airtight container with a lid. You can use a glass jar, the original oil container, or a sealed bottle/jar. Make sure the container is dry and free of any moisture to prevent contamination. Label the container with the date, the type of oil, and the number of times it has been used. Store the container in a cool, dark, and dry place, such as a pantry or cabinet. Avoid exposing the oil to direct sunlight or heat sources, as this can accelerate degradation.

Shelf Life and Reuse:

The shelf life of used deep fryer oil depends on various factors, including the type of oil, the temperature it was heated to, and the food fried in it. With proper storage and maintenance, frying oil can be reused anywhere from two to eight times. However, it's important to monitor the oil for any changes. Used oil takes on the flavour of the food fried in it, so keep this in mind when reusing it. If the oil becomes dark or dirty, smokes excessively before reaching frying temperature, foams at the top, or develops a rancid or musty odour, it's time to discard it.

Disposal:

When the oil has reached the end of its useful life, dispose of it responsibly. Do not pour it down the sink drain, as it can clog your pipes. Instead, solidify it using a product like FryAway and then throw it away in the trash. Alternatively, pour the oil into a sealable disposable container and toss it in the trash. Some communities also have recycling programs that accept used cooking oil for conversion into biodiesel.

Reusing oil

Firstly, it is crucial to allow the oil to cool completely before attempting to handle or store it. Once cooled, the oil should be strained to remove any food particles. This can be done by pouring the oil through a fine-mesh sieve or strainer lined with cheesecloth, muslin, kitchen paper, paper towels, or a coffee filter. This step is important as any leftover particles will burn and make the oil taste nasty when reheated.

Next, transfer the strained oil to a clean, airtight container, such as a glass jar or the original container the oil came in. It is helpful to use a funnel to avoid mess and to label the container with the date, the type of oil, and the number of times it has been used. Store the oil in a cool, dry, dark place, away from heat sources such as the oven, stove, or microwave.

Oil can be reused anywhere from two to eight times, depending on various factors. The type of oil is one factor, with vegetable-based oils with neutral flavours, such as safflower, sunflower, corn, canola/rapeseed, and peanut/groundnut oils, being more suitable for reuse than animal-based fats due to their higher smoke points. The type of food being fried is another factor, with vegetables tending to have the lowest impact on the oil, followed by batters, and then breaded items, which leave the most particles and residue.

It is important to note that with each use, the smoke point of the oil reduces slightly, and the oil takes on the flavour of the food fried in it. Therefore, it is recommended to fry similar items in previously used oil to avoid unpleasant flavour transfers.

There are several signs that your oil has reached the end of its life and should be discarded. These include:

• The oil starts smoking before reaching the cooking temperature or around the target temperature.
• The oil has become very dark, thick, or discoloured.
• The oil starts smelling of the food cooked in it or develops a rancid, musty, or burnt odour.
• The oil is foaming at the top.

Oil degradation

Oxidation

Oxidation is the major cause of oil degradation and is accelerated by high temperatures. It results in the formation of volatile and non-volatile decomposition products, including hydrocarbons, free fatty acids, aldehydes, ketones, alcohols, and lactones. The presence of food during frying can further accelerate oxidation, as water interacts with the oil, leading to a tainted or acidic taste.

Hydrolysis

Hydrolysis occurs when water interacts with oil, causing it to taste tainted or acidic. This reaction is exacerbated by high temperatures, heating and cooling cycles, and the presence of oxidation products.

Polymerization

Polymerization is the process by which large, different-sized clusters of molecules form and accumulate on the oil's surface. These molecules do not dissolve and cause foaming, trapping air under the oil, and increasing the possibility of hydrolysis.

Isomerization

Isomerization leads to the formation of trans-fatty acids, which have been linked to adverse health effects such as cardiovascular diseases and increased risk of certain cancers.

Factors Affecting Degradation

The rate of oil degradation is influenced by various factors:

• Temperature: Higher temperatures accelerate degradation and the formation of trans-fatty acids.
• Frying Time: Prolonged heating increases thermal oxidation and the formation of polar compounds.
• Oil Type: Oils with higher levels of polyunsaturated fatty acids, such as sunflower oil, are more susceptible to degradation.
• Presence of Food: The presence of food during frying can accelerate degradation, particularly when food contains water.

Monitoring Degradation

The degradation of frying oil is typically monitored through visual inspection, tasting the fried food, or measuring chemical parameters such as free fatty acids, total polar materials, and polymerized triglycerides. However, these methods may not be reliable as they are subjective and may not detect degradation until the oil has already become unsafe. Therefore, there is a need for a simple and inline sensing system to continuously monitor frying oil quality.

Oil stabilisers

Fry powder is easy to use. Simply tear open a sachet and add the required amount to your hot fry oil. You can do this every 6-8 hours, especially if the fryer is in use twice a day. Fry powder has an antioxidant effect, acting like a 'vitamin' therapy, which prevents unhealthy breakdown reactions when frying.

Using fry powder will also save you money on energy. It enables the fryer to operate at a lower temperature, cooking the centre of the food better. A lower temperature keeps water in the food and uses it to cook, whereas a higher temperature forces the water out. Uncontaminated oil cooks faster, as it isn't absorbed into the food. Absorption slows down the cooking process, increasing oil usage and leading to oily, bad-tasting food.

There are a variety of oil stabilisers on the market, including Fryclone, Frymaster, Henny Penny, FreshFry, AllPoints, Anets, Pitco, and MirOil FryPowder.

Disposing of used oil

• The Container Method: Pour cooled oil into a disposable container (such as an old sour cream or cottage cheese container) and seal it shut before throwing it away.
• The Freezer Method: Pour leftover oil into an old can and place it in the freezer until hardened. Once firm, scoop the oil out and into the trash with a spoon.
• The Plastic Bag Method: Pour cooled oil into a plastic trash bag that already has some debris inside, such as old paper towels or veggie peels, which can help soak up the grease.
• Recycling: Check with your local waste department or Earth911.com to see if there are places where you can recycle leftover oil.

If you're looking to dispose of larger quantities of oil, such as restaurant amounts, there are companies that will pay to pick up the oil. Some people also use old cooking oil to make biodiesel fuel.

Additionally, it's important to note that oil should not be reused indefinitely. Each time oil is reused, it deteriorates and becomes more susceptible to burning. To test if oil is still safe to use, give it a sniff test. If it smells rotten or rancid, it should be discarded.

Frequently asked questions