What to Do with Leftover Cooking Oil: A Guide

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If you cook a lot, it means you'll go through a lot of ingredients and—almost inevitably—a lot of cooking oil. That means you'll regularly have used oil to deal with, though the actual quantity varies with your cooking style. Used cooking oil isn't like most food waste, which is relatively easy to dispose of in the trash, your compost or a green bin. Disposing of oil safely and responsibly requires a bit of extra effort on your part. Better yet, you can be creative and think of it as a resource to be harnessed and maximized. Either way, we've got plenty of ideas to get you started. Read on below for ways to dispose of cooking oil, ways to reuse it and, of course, ways NOT to dispose of it.

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Part 1: How to Dispose of Used Cooking Oil

You may have a lot or a little, but there are several practical ways to get rid of your used oil.

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1. Wipe it up

Instead of just plopping your pans in the sink and rinsing the oil down your drain (which is a bad idea that we'll get to later), take a moment to blot up the oil with something absorbent. That would usually be paper towels, but if you have other leftovers that are trash-bound—a dinner roll, a piece of bread, a half-portion of noodles—those work just as well. Wipe out your pan with one of those, drop the oily mess in your trash, and you're done. This works only with small amounts of oil, but it's a simple and practical cleanup method.

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2. Pour it into something absorbent

Another way to get rid of a larger quantity of oil, from deep-frying, for example, is to pour it into something absorbent, like that bag of cat litter you've just finished scooping. Other possibilities include sawdust, flour, cornmeal or a shovel full of dirt or sand from somewhere in your garden. Bag up the oily mixture, and drop it in your trash.

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3. Use a cooking oil solidifier

An oil-gelling powder is by far the most fun option, and it's fascinating to watch (as you may have seen on TikTok!). There are powders sold under a variety of brand names that you can simply sprinkle right into the hot oil in your fryer. The powder—a plant-based fat itself—causes your cooking oil to congeal into a semi-solid gel once it cools to room temperature. You can just plop the cooled disc of congealed oil right into your trash can or green bin.

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4. Seal it in a container

If you have more oil than you can conveniently blot up, pour it into a sealable container—a Mason jar, an emptied milk carton, a used deli container or pickle jar—and then put that in the trash. Word to the wise: Don't pour hot oil into a container that could melt, though. (If all you have is a plastic container, let the oil cool first.) You can also accumulate oil in a jar, which you can dispose of when it's full (or decant the oil periodically into a disposable container whenever you've got one). Don't put your frying oil in plastic bags, even after it has cooled, because bags aren't usually strong enough to keep the oil sealed.

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5. Find an oil-recycling program in your area

The recycling industry sees used cooking oil as a resource, not a waste problem, and many urban areas have used-oil recycling programs. Check with your municipality or its waste-removal contractor to see if there's a recycling center in your area where you can drop off your oil, or even a household hazardous waste drop-off. If all else fails, talk to restaurants near you to see if they'll let you add your oil to their recycling bin. Some restaurants pay for it to be hauled while others sell it to recyclers, so they may or may not be open to the idea.

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Part 2: How to Reuse Used Cooking Oil

If you're the kind of person who hates to waste anything, there are lots of ways to make use of used cooking oil.

1. Compost it

If you compost in your garden, adding small amounts of used vegetable oil to the compost pile can be beneficial. Earthworms not only love it but also get a nutritional boost. Just don't go overboard (small amounts only, please), and be sure you're using only vegetable oil. Animal-based fats, or oil that's been used to cook meats, will cause bad odors and attract unwelcome visitors to your compost.

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2. Give Fido a treat

Adding small amounts of leftover cooking oil to your dog's kibble will make it a red-letter day for your favorite canines and help keep their fur glossy as well. (Do this sparingly if your pup is already on the hefty side.)

3. Feed it to the birds

You can mix your used cooking oil with grains, seeds and peanut butter or suet to make bricks or balls to go into your bird feeder. If you keep chickens or other domestic poultry, you can stir it into their feed as well.

4. Use it in an oil lamp

If you keep a few oil lamps around for power outages (or just the look), you can burn leftover cooking oil in them. Just strain out any bits of food through a mesh strainer, cheesecloth or an old cleaning cloth before filling the lamp. Your house may smell like french fries or fried chicken as a result, but that's not necessarily a bad thing!

Homemade Lamp Oil

5. Use it on squeaky hinges

Got creaking doors around the house? Instead of reaching for the WD-40, dip a clean rag into a few tablespoons of your used oil and use it to lubricate the hinges. It's also a good occasional fix for things like pliers and adjustable wrenches if they're not moving smoothly.

6. Weatherproof your garden tools

Wiping down the wooden handles of your garden tools periodically with a thin layer of oil will help keep them from deteriorating due to exposure to sun and rain (or sweat from your hands). Similarly, oiling the metal "business end" of your shovels, hoes, forks and rakes will help keep corrosion away.

7. Make soap

Soap was originally made from households fats, and it's a fun science project to do for yourself or with kids. There are plenty of tutorials online, but they mostly boil down (pun intended) to stirring fats into a mixture of lye and hot water. You might not want to do this on a regular basis, but it's a fun rainy-day project.

8. Put some biodiesel in your tank

Commercial recyclers often turn used oils into biodiesel, for powering trucks, buses and heavy equipment. You can do this at home on a small scale, though it's probably not worth it unless you supplement your own used oil with a larger supply (again, talk to your local restaurants). If you're the DIY type and have a thirsty diesel vehicle or two, just search "DIY home biodiesel" to get a feel for what's required.

Warning

The lye used in soap making is caustic, and the chemicals used in making biodiesel are caustic and flammable. Make sure you understand the process before you start, follow all safety recommendations and wear appropriate protective equipment.

9. Make a nontoxic pesticide for your garden

A common general-purpose DIY pesticide calls for a mixture of oil and dish soap in water. Why use brand-new oil when you can "upcycle" used oil instead? The same mixture works well against some forms of mold and mildew on plants, so use it freely.

10. Polish wood furniture

A mixture of used vegetable oil and distilled vinegar makes a good polish for your wood furniture, helping restore its natural sheen and protecting it from drying out.

11. Preserve wicker or rattan furniture

Similarly, you can simply rub wicker or rattan furniture with clean used vegetable oil to restore its sheen and—in the case of patio furniture—protect it from the elements. Be careful not to use animal fats for this, or vegetable oil that's been used to cook meats. Both can result in unpleasant odors, and attract unwelcome attention from animals.

12. Just...reuse it

One other option for reusing your oil is the simplest of all: Save it to use another time. Pour the oil through a fine-mesh strainer or cheesecloth to remove any food debris, and then keep it refrigerated in a Mason jar. The next time you feel like serving fried foods, just pull out your jar of oil and you're good to go. Oil that's used for breaded or battered foods can usually be reused three or four times, while oil that's only ever been used for vegetables or french fries can be good for up to eight uses. Over time, that can add up to significant savings.

Tip

If you use your fryer a lot, you might want to keep separate batches of oil for specific foods. You probably don’t want to fry chicken in oil that’s been previously used for fish, for example.

Part 3: How NOT to Dispose of Used Cooking Oil

We've talked lots about how to dispose of used cooking oil properly, but what about ways that aren't so good? Well, there are a few of those as well (unfortunately, most of them are pretty common).

Here are some "Don'ts" when it comes to used cooking oil:

1. Don't: Dump it straight into the garbage

If the oil is hot, it will almost certainly melt your trash bag—and a plastic kitchen trash bin may get damaged as well. Even if you let the oil cool first, there's a high likelihood the bag will leak and make a mess for you to clean up.

2. Don't: Put it down drains

Pouring the oil down your sink drain, or into the garbage disposal with your food scraps, isn't a good idea either. Vegetable oil is liquid at room temperature, but it won't necessarily stay that way once it reaches your pipes or the sewer system. It may already be mixed with animal fats from the food you've cooked, which will make it congeal as it cools. The drains are also full of cleansers and other chemicals that can react with fat, causing it to solidify (this is how soap-making works, remember?), forming "fat-bergs" that can clog your pipes, your septic system or, on a larger scale, the entire sewer system of a community (that last one's not just on you, of course).

3. Don't: Pour it down the toilet

This is just as bad as pouring it down your sink, for all the same reasons plus a few more. For starters, it increases the likelihood of your toilet clogging and backing up. Second, it makes your toilet bowl greasy. Third, if the oil is hot and your aim is poor, there's a risk you could crack the porcelain. Totally not worth it.

4. Don't: Dump it outdoors

Pouring used cooking oil onto the ground isn't a good idea, either. If there are any animal-based fats or meat flavors infused into the oil, it may attract unwelcome critters or create rancid aromas. The oils will eventually wash through your soil into the water table (bad for well-water users) or out into storm drains, where it can damage ecosystems or create blockages.

One Final Note...

We've talked a lot about reusing and recycling your used cooking oil, but there's one other way to approach the problem of cooking oil disposal. That's simply to use less of it in the first place (that whole "ounce of prevention" ethos). Some fats are better for you than others, and they're essential to a healthy diet, but it's definitely possible to have too much of a good thing.

Simply trading in your deep fryer for an air fryer is a good start, considering that air fryers use a fraction of the oil. You can also "oven fry," in a conventional or countertop oven (some new models even have "air fry" settings) by misting your food lightly with oil and then cooking it on a sheet pan. Other options include making better use of nonstick pans, and you can even line a skillet with a piece of parchment paper to take advantage of its nonstick properties (though this takes practice and works best with vegetables).

Whether you choose to reduce, reuse or recycle your cooking oil, the end result will be more practical (and more environmentally friendly) that just putting it down the drain.

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