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Should You Leave Cooking Oil in Your Cast Iron Skillet?

So you made fish fingers or fries in your cast iron skillet, and they turned out delicious. Now, you feel full and happy. But you’re also a bit too lazy to clean up after yourself (that’s the part of home cooking almost nobody likes).

Is it okay to leave cooking oil in your cast iron cookware?

It’s not a good idea to leave cooking oil in your cast iron skillet or Dutch oven. The oil can go rancid if exposed to the elements for an extended period of time, and you will have to throw it away.

When cooking oil becomes rancid, it reacts with the elements and bacteria in its environment. In the process, the oil breaks down into fatty acids that give it a bad taste and an unpleasant odor that many describe as sour and musty.

Cooking oils contain polyunsaturated and monounsaturated fats and a certain amount of moisture, ranging from as little as 0.005% to as much as 0.03%, which can be chemically reactive to cast iron. These reactions can lead to dietary iron leaching into the oil and the oil itself oxidizing and turning rancid quicker in certain conditions.

In other words, you don’t want cooking oil sitting in your cast iron cookware for too long (it’s not the same as the carbonated layer of oil that comprises its seasoning). The best thing to do is clean it by hand shortly after you’re done frying with it.

But what if you plan to reuse the oil?

After all, cooking oils in the grocery store don’t always come cheap, and there’s nothing that necessitates you to throw them away right after the first use…

Can You Reuse Cooking Oil?

Your last batch of French fries made you realize that your cooking oil is running out. You’re wondering if it’s okay to reuse the oil, but don’t know how. Well, I’ve got some answers for you!

In general, cooking oils with a higher smoke point, such as avocado oil, rice bran oil, safflower oil, and sunflower oil, are better suited for reuse than those that burn at lower temperatures, like extra virgin olive oil.

If you plan to reuse cooking oil, let it cool down completely, strain it from any leftover bits and pieces of food, transfer it to an airtight glass jar or plastic food storage container, and store it in a cabinet or your pantry.

Stored in an airtight container at room temperature, used cooking oil has a shelf life of 3-4 months.

To extend shelf life, make sure it’s filtered from food particles and kept away from heat sources, such as the stove or the fridge, and direct sunlight, such as in a sunlit kitchen or on a windowsill.

Butter can also be reused, but you should store it in your fridge, where it will keep for 1-2 months. When you’re planning to cook with it, simply scoop it out and let it melt in your skillet as you bring it to heat.

How Many Times Can You Reuse Cooking Oil?

Did you know that cooking oil can be reused as many as nine times? Unless you’re frying breaded or battered foods, in which case the oil will can be reused two to three times less.

How many times can cooking oil be reused?

When it comes to reusing cooking oil, the one thing you need to know is that it will degrade with every use until, sooner or later, it becomes impractical to use (and should be discarded).

This is because the smoke point of a vegetable oil or animal fat, the threshold at which it stops to glisten and shimmer and starts to break down and burn, will become lower and lower with every reuse. At some point, the oil or fat will burn at low to medium heat, imparting your food with an acrid smell and bitter taste (that come from toxic compounds potentially harmful to your health).

So the trick is in roughly knowing the number of times you can do this.

According to Cook’s Illustratedhow many times you can reuse a cooking oil depends on the type of food you’re making with it.

Breaded or battered foods will degrade an oil faster, and you should discard it after 3-4 uses. An oil used for shallow- or deep-frying cleaner food items, like French fries, can be reused as many as 8-9 times.

It’s a good idea to reuse cooking oil for preparing the same (or similar) recipes unless you don’t mind it imparting a funky aftertaste to your food. For example, deep-frying chicken wings in oil that’s previously been used for battered hake will give them a fishy smell and taste.

How to Dispose of Old Cooking Oil

Time to clean out your kitchen and get rid of that sticky old cooking oil. But do you know how? And what’s an environmentally friendly way to do it?

Don’t dispose of old cooking oil in your sink or toilet; it can cause blockages. Instead, pour small amounts of it into your compost pile, take it to a recycling site that accepts used oil, or, if none of these two options are available to you, seal it tightly and throw it away in your trash can.

Flushing used oil down the sink or toilet isn’t necessarily the best idea. Just like it can clog your arteries, it can build up on your drains and sewage pipes, causing a stubborn blockage.

As much as you like hanging around with your friendly neighborhood plumber, you probably don’t want to have to call them. So try one of my oil disposal techniques instead.

You can dispose of old cooking oil by adding small amounts of it to the compost pile, The Worm Monger, a blog devoted to reducing household waste, says.

It’s one of those complex substances that take longer to break down than the rest of the foods in your fridge. Adding too much of it can cause rot, displace water, and kill the compost, so don’t go crazy by adding too much of it at once.

Readers in the United States can use Earth911’s recycling locator to try to find a recycling location that accepts cooking oil in their area. Some may only be available during the holiday season.

If you don’t have a compost bin and can’t find a recycling location nearby, seal the old cooking oil (in a bottle or container) and dispose of it in the garbage.

In Conclusion

While nothing is stopping you from keeping cooking oil in your cast iron skillet, the right thing to do is store it for reuse (or dispose of it properly in case it’s no longer usable) and clean the skillet in soapy water shortly after you’re done.

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Written by

Jim is the former editor of Home Cook World. He is a career food writer who's been cooking and baking at home ever since he could see over the counter and put a chair by the stove.