How can you tell if your restaurant's fryer oil is fresh?

Sure, there are other ways to determine the freshness of cooking oil, and just as many opinions on how often a fryer vat should be switched out with fresh.  But using your sense (or senses!) is often the best test. 

How does it smell?  Oil that has turned, or nearing that point, has an acrid, bitter smell. Oil picks up the smells and flavors of the food cooking in it, just as the food can pick up the smell and flavor of the oil. If too much food has been run thru a batch of oil, it can affect the taste of the food coming out of the fryer.

How does your food taste?  Are your fries still crisp, nicely browned and tasting like, well, french fries? Or have they picked up flavors or aromas from other foods nearby?  

How does the oil look?  The longer oil is used, the more the molecules break down. Spent oil tends to be darker, often with a thicker, gummy consistency.  Degraded oil can also have a frothy or soapy appearance.

Forget the senses, what's the science?

  • Know the type of oil you are using.  Different oils have different smoke points, and different shelf lifes.  Oil that can withstand higher temperatures (peanut, canola and vegetable oils versus the lower temp-restricted olive oil) generally have a longer life.  But there’s a flip side.  Oil that is heated to too high a temperature will degrade more rapidly.
  • Proper temperature control.  Generally speaking, optimum frying temps for most oils and most foods is 330-350 degrees. Care should be taken to never exceed 375 to get the most out of your oil. Fortunately, modern commercial fryers do an excellent job of maintaining the proper temperatures for your fried foods.  It’s up to the restaurant manager to make sure their fryers are turned off and oil is cooled and covered when not in use.

How long should oil last?

Ask five chefs and you’ll likely get five answers, from twice a week, to every two weeks, to every couple of months or longer for low volume fryers. Much of it depends on what you are cooking. 

  • Coated foods will degrade oil more quickly than raw potatoes.
  • Is water being introduced into the oil?This is not only dangerous, but degrades your oil. Be sure to drain or shake excess water from your food away from your fryer before adding it to your hot oil. 
  • Don’t allow oil to sit uncovered when not in use.  Like water, air can also quickly degrade oil.

How can you extend oil life?

  • Don’t overload your fryer Your food will cook more evenly at a stable temperature if it has room to move in the vat.
  • Lower frying temps give the most life from cooking oils.
  • Keep your fryers clean – but make sure you follow the recommendations of your fryer manufacturer. And dont forget to clear off food particles from the heating elements when you clean your vats.
  • Filter the oil –  this can be your best friend. Many experts, as well as fryer manufacturers, recommend filtering oil twice a day, after lunch and dinner runs.  At a minimum, train your workers to routinely skim food particles from oil throughout the day. 
  • A full change-out to fresh oil is preferably to topping off When adding fresh to used, you can never determine how much old oil is being used to fry your fresh foods, and maintaining quality control, and costs, become harder to manage.


You're the expert in frying. We're the expert in what to do with your waste grease.

<h4>You're the expert in frying.&nbsp; We're the expert in what to do with the grease when you've finished with it..&nbsp;</h4>

And what does a responsible restaurant manager do with the used cooking oil? 

  • NEVER discard used cooking oil down a drain (clogs and costly plumber bills, as well as city fines) 
  • Dont DUMP IT into the trash bin (attracts rodents, smells bad enough to turn away customers, and could cause grease spills, possibly incurring fines). 
  • Partner with a reputable grease service provider who will take your waste oil and turn it into something of value. 

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