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How Often Should You Change the Oil in a Deep Fryer?

I worked in many kitchens for more than 20 years, and one of the questions that often came up from customers and employees alike was how often should you change the oil in a deep fryer.

Deep fryer oil should be changed after 6-8 uses for non-breaded vegetables & 2-4 uses for breaded items or fatty meats & fish.

But there’s more to deep-frying oil than just that, including how to tell if the oil has gone rancid to what the best ways of disposing of cooking oil are when you do change it.

So let’s keep cookin’

If you’re looking to buy any small kitchen appliance, don’t forget to check out my Recommended Products Page (click to see my page) which breaks down all my best picks by category.

I always hand-select items that I either own, have used, or have researched well to ensure they are great items. I also give not only top of the line as well as inexpensive alternatives so my choices work for any budget.

How long does oil last in a deep fryer?

Keep your deep fryer oil a maximum of 3 months. After cooking, allow the unit and oil to cool for 2 hours. Then pour the oil into a container through a strainer or cheesecloth. Place a lid on the container, and refrigerate for best results. 

The lifespan of your cooking oil before needing to be changed depends on a few factors, such as:

  • How often are you using it? (daily, weekly?)
  • What are you frying in it? (ie: fish will impact it differently than potatoes)
  • Are you frying really bready items (which leave a lot of debris in the oil)
  • What kind of oil are you using? (refined peanut or vegetable oils last longer)

Those are some considerations you’ll want to take before deciding when to change your oil and there really isn’t a one-size-fits-all approach to knowing when to change the oil in a deep fryer.

What are the best signs to look for in “old” oil that needs to be changed?

  • Foam on the surface of the oil (when hot)
  • A fishy smell (even if you haven’t been frying fish)
  • The oil smokes a lot more than it did before
  • A significantly darker color than the original color

If you absolutely have to have a number, use the following as a general guide, but always use your senses (including common sense!)

Also know that generally speaking, oil in a deep fryer lasts longer than oil used to fry in a skillet.

Type of food you fry most often Approximate # of uses before changing is needed
French fries, other non-breaded items 6-8 uses
Breaded or crumbly foods 3-4 uses
Fish (breaded) 2-3 uses
Vegetables (non-breaded) 6-8 uses
Meats & Poultry (non-breaded) 3-4 uses (with fattier foods like bacon, air on the low side)

Can you reuse oil in a deep fryer?

Yes, you can reuse the oil from a deep fryer. After the oil has cooled (about 2 hours), strain through a filter or cheesecloth into an airtight container with a lid. Refrigerate for best results. Continue to reuse the oil for a maximum of 8-10 uses or until the color or smell has degraded.

Deep fryers make food crispy by a process known as the Maillard reaction.

The Maillard reaction is named for French chemist Louis-Camille Maillard and refers to a chemical reaction with the amino acids in the oil. This gives food a crispy texture and darkens the color of both the food and the oil.

Unfortunately, the more times you do this, the shorter the lifespan is of the oil. The best strategy for reusing oil in a deep fryer is to clean it after every use and store it properly.

To clean your deep fryer oil (or cooking oil in a skillet), do the following:

  • Use a skimmer to remove any food particles or debris
  • Pour the oil through a filter into a clean, dry pot
  • Stop before you get to the bottom of the oil (where there may be more debris)
  • Cover the pot and allow to cool completely
  • With a funnel, pour the oil back into the original container or any airtight container
  • As with any oil, store in a cool, dark place, away from windows and heat sources like a stove

Now if you love fried foods but hate the fat and calories that can come with it, check out my article on the Significant Advantages of an Air Fryer (click to read on my site).

One of the coolest advantages of an air fryer is their ability to cut the cooking time in half. But that’s just 1 of the 13 advantages I review in my post, so you’ll want to check out the rest!

How often should Restaurants change fryer oil?

Most restaurants that use their deep fryer(s) regularly will want to change their oil twice a week. However, some restaurants may have 1 fryer dedicated to fish or breaded items which may require more frequent changes.

It stands to reason that restaurant deep fryers get a LOT more use than home kitchen fryers or skillets.

It’s also true that restaurants can’t afford to put out mediocre food caused by oil that is broken down and not good anymore. Mediocre food = bad reviews and fewer visitors.

So just know that restaurants will (hopefully) be changing their oil a lot more frequently than we do at home.

One other consideration though is that many restaurants have more than one deep fryer. So they have some dedicated to meats and fish and others dedicated to vegetables. This helps keep the foods that can break down frying oil faster limited to one of their fryers instead of all of them.

Other considerations include:

  • Don’t top off your oil, just change completely as needed
  • Salt food after it leaves the fryer
  • Keep the fryer set to a lower temp of around 375°
  • Perform a deep clean of the fryer every 3 months

Speaking of frying, if you love french fries, but prefer to buy bags of frozen fries rather than the somewhat labor-intensive method of cutting your own, you might be confused about whether you can fry them.

In short, while some folks do bake frozen french fries, they are actually GREAT in the deep fryer.

It is essential, however, that you use the right kind of oil to fry your frozen french fries (click to read my post). So take a moment and review the best oils for that and especially the 1 you want to avoid!

How do you get rid of deep fryer oil?

To dispose of deep fryer oil, first, allow the oil to cool and turn solid. Then place the oil into a box or double-layered plastic bag and place it in your trash can. Do not rinse down your drain and never pour it into your yard while hot as it can kill the grass.

This is a biggie as there are some big no-nos for disposing of fryer oil.

Restaurants have what is known as a grease trap; basically a vessel for storing old cooking oil. They use a service to come pick up the oil when the vessel is full.

If you have ever been outside a fast-food restaurant and seen a big truck and smelled something horrible, you can bet it was the grease-trap emptying day!

For home kitchens, let’s start with what NOT to do.  

  • Don’t pour it down the drain
  • Avoid pouring it in the yard (it will kill or at least discolor the grass)
  • Don’t pour into a compost bin or pile

The best strategy is to either:

  • Allow to cool, pour into a container with a lid, and throw in the trash
  • After cooling, place in a bowl in the freezer until it’s thick and scoop into the trash

It’s also worth noting that with the biodiesel industry has cropped up over the last decade or so that many restaurants do actually sell their used cooking oil to be turned into biodiesel fuel.

I’m not aware of that being available for home uses, but it may be worth Googling in your area, especially if you go through a lot of oil.

How can you tell if frying oil is bad?

You’ll know your frying oil is bad when you see foam, the coloring is significantly darker, or it smells bad. Frying oil goes through stages from good to bad, turning darker in color with the smell getting stronger and sourer.

For frying oil, it doesn’t instantly go from good to bad.

Here are the stages:

  • Foam or frothiness on the surface of the oil (when hot)
  • The color will be significantly darker
  • It will smell bad

But beyond just the oil breaking down, oil can also go rancid, which is even worse.

Rancidity is technically named “hydrolytic rancidity” and refers to a process where the oil starts to break down due to oxidation. This turns the oil into fatty acids which smell bad.

Oils that turn solid at room temperature (coconut oil, lard) are less likely to turn rancid than other oils. The oils most likely to turn rancid are ones that have already been heated in the process of packaging them, such as any oil labeled “toasted”.

There are a few signs to check for oil being rancid which include:

  • It smells soapy or bitter or has a chemical smell almost like paint thinner
  • When you pour the oil on your finger, beyond being thick, it feels sticky

The things that can cause the oil to go rancid include:

  • Excess heat (being too close to the stove)
  • Too much sun (sitting on your kitchen counter in front of the window)
  • Age (that bottle of toasted sesame oil that’s been in your pantry for 2 years)

And before you think this is just for fryer oil or cooking oil, know that old, out of date bags of chips on the grocery shelves can go rancid too, as can any packaged food made with oil.

Luckily, it’s pretty easy to tell by smell when a bag of chips has gone rancid.

Wondering if you can leave your oil in your deep fryer when you’re done with your meal?

It is a great question and there’s a lot of confusion around that. But I go into detail on that in a recent article which breaks down everything you need to know.

I was really surprised at just how long the oil lasts if you just do 1 thing after each use! Just click the link to read it on my site.

Final Thoughts

In this article, we took a look at the world of deep fryers and cooking oil.

We examined how often to change the oil, what foods make the oil go bad faster, how to clean the oil, and even how to dispose of bad cooking oil properly.

Ultimately, we answered the question of how often should you change the oil in a deep fryer with a range of 2-3 uses for fatty meats, fish, or breaded items and up to 6-8 uses for clean vegetables.

But always use your senses to check the oil before every use.

What’s your favorite thing to deep fry?

If you’re looking to buy any small kitchen appliance, don’t forget to check out my Recommended Products Page (click to see my page) which breaks down all my best picks by category.

I always hand select items that I either own, have used, or have researched well to ensure they are great items. I also give not only top of the line as well as inexpensive alternatives so my choices work for any budget.

Jeff Campbell