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How to Tell If an Oil Is Rancid

By Kathleen Brennan Published

Oil doesn't keep forever. To learn when it's time to ditch the bottle, read on.

Rancid oil can ruin your dish. But what is rancid oil exactly? And how can you tell if your oil has gone bad?

To find out, we talked to Eric Decker, a professor in the Department of Food Science at the University of Massachusetts Amherst. Decker explained that culinary oils are mostly composed of triglycerides; over time, these triglycerides oxidize, or react with oxygen, and decompose into small molecules. The good news is that some of these small molecules smell, so in the case of refined oils such as vegetable or canola oil, which have relatively little odor or flavor, it’s easy to determine whether or not it’s rancid. Simply pour a small amount into a spoon and give it a quick sniff. If it has an “off” odor—perhaps like crayons, metal, or something sour—it’s past its prime. 

To see if olive oil is past its prime, pour some into a spoon and sniff it. Sour odors mean that it's rancid. It'll have an off smell if it's gone bad.

Unrefined oils, including extra-virgin olive oil, are trickier. According to Decker, they have aromas and flavors that can mask rancidity, so it’s hard for nonexperts to know if they are rancid by smell alone. As such, Decker recommends tasting the oil. Pour some into a cup and, if needed, warm the cup in your hands to get the oil to room temperature. Take a small sip (about a teaspoon’s worth) and suck on it as if you were pulling liquid through a straw, without swallowing or exhaling. If it is rancid, it will have an off-flavor that results from the combination of the olive oil flavor and the rancidity aromas. Because this flavor can be hard to describe, Decker recommends tasting—and smelling—any oil the first time you open the container so that you have a baseline to work from. This technique is especially helpful in the case of olive oils.

Lastly, rancid oils can also take on a stickiness, so if the container feels tacky around the inside of the spout, it might be time to toss it.

All About Oils

Here’s everything you need to know about selecting and using cooking oils.

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JOHN C.
16 days

Absolutely the best chicken ever, even the breast meat was moist! It's the only way I'll cook a whole chicken again. Simple, easy, quick, no mess - perfect every time. I've used both stainless steel and cast iron pans. great and easy technique for “roasted” chicken. I will say there were no pan juices, just fat in the skillet. Will add to the recipe rotation. Good for family and company dinners too. I've done this using a rimmed sheet pan instead of a skillet and put veggies and potatoes around the chicken for a one-pan meal. Broccoli gets nicely browned and yummy!

Absolutely the best chicken ever, even the breast meat was moist! It's the only way I'll cook a whole chicken again. Simple, easy, quick, no mess - perfect every time. I've used both stainless steel and cast iron pans. great and easy technique for “roasted” chicken. I will say there were no pan juices, just fat in the skillet. Will add to the recipe rotation. Good for family and company dinners too.

MD
MILES D.
JOHN C.
9 days

Amazed this recipe works out as well as it does. Would not have thought that the amount of time under the broiler would have produced a very juicy and favorable chicken with a very crispy crust. Used my 12" Lodge Cast Iron skillet (which can withstand 1000 degree temps to respond to those who wondered if it would work) and it turned out great. A "make again" as my family rates things. This is a great recipe, and I will definitely make it again. My butcher gladly butterflied the chicken for me, therefore I found it to be a fast and easy prep. I used my cast iron skillet- marvellous!

CM
CHARLES M.
11 days

John, wasn't it just amazing chicken? So much better than your typical oven baked chicken and on par if not better than gas or even charcoal grilled. It gets that smokey charcoal tasted and overnight koshering definitely helps, something I do when time permits. First-time I've pierced a whole chicken minus the times I make jerk chicken on the grill. Yup, the cast iron was not an issue.