10 Smart Uses for Rancid Cooking Oil (And 9 Things You Should NEVER Use It For)


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Last Updated: July 18, 2021

On blogs, forums and sites like Reddit, you’ll find lots of lists of things to do with rancid oil. Surprisingly though, a lot of the recommended uses for old or used cooking oil are actually very bad ideas.

For example, you definitely do not want to oil hinges with rancid oil: it will attract dirt and quickly gunk up the hinges.

Below, I’ll go over the uses for rancid oil which really work. I’ll also cover which things you shouldn’t do with rancid oil. 

Uses for Rancid Cooking Oil

1. Season Cast Iron Pans

Cast iron needs to be seasoned in order to prevent rust and sticking.  You can use rancid oil to season the pot.  Bear in mind that oils with high smoke points, such as grape seed oil, work best for seasoning cast iron.

2. Bio-Diesel Fuel

A lot of people even collect old cooking oil from fast food places to make their own bio-diesel.  You don’t have to use it on your car.  Bio-diesel can be used in lawnmowers, tractors, and other machines.

3. Fire Starters

To make your own fire starters, dip dryer lint or cotton balls into the rancid oil.  Then wrap them in wax paper.  Put a flame next to it and the rancid cooking oil will light up quickly and burn for a long time.  Used oil from your deep fryer works just as well for this too.

Also see best tinder for firestarting

cooking oil fire starters

3. Starting Charcoal

Sprinkle a bit of the rancid oil on your BBQ charcoal and it will light right up.

4. Oil Lanterns

It’s generally better to use non-rancid oil in lanterns; the rancid oil will produce more unhealthy fumes. However, rancid oil is fine for oil lanterns used outdoors and for emergency lanterns.

Read how to make your own vegetable oil lantern.

cooking oil emergency lantern

5. Remove Glue and Sticky Things

Want to get all of the labels off of a bunch of jars? Or get a bumper sticker off your car? Peel off as much of it as you can.  Then apply a thin layer of rancid oil over it and let it sit.  The oil will break down the glue and make it easier to wipe off the sticky residue.

6. Suet Cakes for Feeding Birds

Suet cakes are used to feed birds.  Even though they are traditionally made with suet, you can use rancid cooking oil.

7. Animal Feed

Lots of people add rancid cooking oil to feed for chickens, dogs, or cats.  The extra fat can boost their health and improve their coat. Note that rancid cooking oil isn’t any healthier for animals than it is for us.  Rancid cooking oil is probably still better than whatever old oil is in store-bought pet feed.

8. Weed Killer

Various studies and anecdotal accounts show that rancid oil does indeed kill weeds.  For tougher weeds or saplings, you’ll want to pour the oil on while it is hot.

9. Insecticide for Plants

Cooking oil is a natural way to control insects and spider mites in your garden or on house plants. When applied to the leaves, it will create a protective coating against pests. It also helps keep other natural insecticides in place.

According to Growers Trust: mix olive oil, two to three cloves of garlic, hot sauce, dish soap, lemon juice, and water together. Strain through a cheesecloth, and spray on plants two to three times a week.

10. Polish Stainless Steel

Almost all stainless steel cleaning products contain oil.  Instead of buying these expensive products, you can just use your old oil to polish stainless steel. Here’s how.

Do NOT Use Rancid Cooking Oil to:

There are all uses for rancid cooking oil that I found on other websites.  Obviously, the people have never tried them or they would know it’s actually a very bad way to use old oil!

Never use rancid oil to…

Seal Wooden Cutting Boards and Knife Handles

Wood products do need to be periodically sealed to keep them from drying out and cracking, getting stained, or harboring bacteria.  However, it’s generally not a good idea to use rancid oil on wood.  It will continue to go rancid and give your cutting board a bad smell.

Rancid walnut oil,  flax oil, and non-processed coconut oil can be used with caution on wood cutting boards.  However, do not use rancid vegetable oil on wood.

Polish Furniture

Using vegetable oil to polish furniture will make your furniture stink as the oil goes rancid.  On top of that, as one woodworker pointed out on Reddit, cooking oil “does a poor job as a polish.”

Polish Leather

Also, don’t polish leather with rancid oil. It not only will start to stink but it’s hard to apply vegetable oil evenly to leather.  You’ll end up with splotchy dark areas.

Treat Wicker and Rattan Furniture

You really don’t want to use rancid oil on wicker or rattan.  They are highly absorbent materials and have a high surface area (and thus a faster oxidation rate), so wicker or rattan will start to smell bad very quickly.  On top of that, the oil will attract dirt and stains.

Lubricating Squeaky Hinges and Moving Parts

Applying cooking oil (rancid or not) to hinges will temporarily stop squeaks. It will also temporarily unstick moving parts, like the pivots on gardening sheers.

However, vegetable oil will attract dirt. It’s only a matter of time before the parts get so gunked up that they won’t move well anymore.  Then you’ll have to deal with cleaning up the gunky rancid oil before applying lubricating oil actually meant for hinges!

Put On Compost

There is a lot of debate as to whether you can put rancid or used cooking oil on compost heaps. The consensus is this: Amateur composters should avoid putting any oil into their bins because it can slow down composting and attract pests.

However, cooking oil is a fat and will break down in compost bins. Thermophilic bacteria actually love it.  So rancid oil can go in the compost bin but only if you do have a serious compost bin going, know how to handle your greens and browns, and know how to keep a pile warm.

Fertilizer for Plants or Lawn

Cooking oil (rancid or not) should not be used to fertilize plants. Oil repels water and could block the plant from getting enough water.  It also might attract pests like rodents to the plant.  Don’t try it!

Beauty Products

Do not use rancid oil in beauty products like DIY lip balm, skin cream, hair relaxer, or soaps.  Just like how you shouldn’t eat rancid oil, you also shouldn’t put it on your skin. Not only is the rancid oil devoid of nutrients for your skin, but it can cause redness and inflammation.

Homemade Essential Oils and Herbal Extracts

Don’t use rancid oil to make herbal remedies like essential oils and extracts.  Rancid oil is toxic and you don’t want it to the basis of anything which is supposed to be medicinal.

What other ways can you think of to use rancid oil? Let us know in the comments section below.

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