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Rid Your Pantry of Icky Rancidity

Once you know what rancid food smells like, there’s no mistaking it! Learn how to tell when nuts, seeds, oils, whole grains, and other foods turn rancid and what you can do to prevent it.

Photographs by Rachael Nusbaum

It’s a major disappointment when you look forward to baking a loaf of whole-wheat bread, only to open the bag of flour and discover it smells … off. Or when you bite into a candy bar with nuts and get a flavor that makes you scrunch up your face.

What causes those bad smells and flavors? Rancidity. It’s a concept you’ve probably heard of before, but might not know how to detect in real life. You don’t need a degree in food science to know when food is rancid. Once you know why foods go rancid and which ones do it most often, you can keep rancid ingredients out of your kitchen and diet. Because rancid foods aren’t just icky to eat. They’re bad for your body, too. 


Jump ahead to:

Definition of rancid food >>

Why does food turn rancid? >>

Health effects of eating rancid food >>

How to tell if food is rancid >>

Can you fix rancid oil? >>

Common foods that go rancid >>

How to keep foods from going rancid >>

Recipes for healthy nuts, oils, whole grains, and seeds >>


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Definition of rancid food

What is rancidity? It happens when fats and oils oxidize, changing the structure of the fat molecules. Oxidized fat produces short-chain fatty acids that have a strongly unappealing odor and flavor — nature’s way of telling us to steer clear of these foods.

It’s not only foods that go rancid. Beauty products that contain oils (like lip balm, lipstick, and foundation) can go rancid, too. 



Why does food turn rancid?

Light, heat, and certain metals and enzymes trigger rancidity, while antioxidants help prevent it. Often, improper storage makes food go rancid.

Food needs to contain oil to go rancid. This can be oil that’s either naturally in the food (like nuts) or added to the food (like crackers). Even pet food can go rancid. Any cooking oil can go rancid, but some, like safflower oil, are naturally more prone to it. Meanwhile, fats like coconut oil and extra-virgin olive oil are more stable, thanks to naturally present antioxidants like vitamin E.  



Health effects of eating rancid food

Is rancid food harmful? It is, but its effects are long term. Eating a rancid nut won’t give you the kind of food poisoning that sends you running to the bathroom. Regularly consuming rancid food over a period of time, though? That’s the real danger.

The fat in rancid foods breaks down into toxic compounds. They contain free radicals that can damage cells and arteries. Free radicals are associated with heart disease, cancer, obesity, diabetes, and other health conditions. 



How to tell if food is rancid

We’ve all encountered rancid food at one point, but how do you know for sure? Use your senses. 

  • Smell: The number one indicator. What does rancid food smell like? Musty, chemical, or harsh. Think of old crayons or old makeup. (If your makeup is rancid, throw it out, just like you’d pitch rancid food.)

  • Taste: Rancid food tastes bad. It can taste bitter, metallic, musty, or just plain off. Have you ever had one peanut M&M that tasted weird in a bag of good ones? It’s because that peanut was rancid. 

  • Appearance: Rancid oils in a bottle may become a darker shade. 

  • Feel: When a bottle of oil is rancid, there can be a sticky film on the outside. 



Can you fix rancid oil?

Nope. Once food’s gone rancid, throw it away. It tastes bad, smells bad, and is bad for you. 



Common foods that go rancid

Any fat can go rancid, but fats that are solid at room temperature (such as butter or coconut oil) are less prone to rancidity, because they are more stable. 

Here’s a rancid food list. Many of these foods offer health benefits when they’re nice and fresh, so don’t stop eating them. Just make sure to follow our storage tips below.  

  • Nuts, such as walnuts, peanuts, and pecans. Almond flour is made from nuts, so it can go rancid, too. 

  • Seeds, such as flaxseed, sunflower seeds, pumpkin seeds, and sesame seeds. 

  • Whole grain flours, such as whole wheat flour, rye flour, and buckwheat flour. Unlike refined flour, whole grain flours contain the germ, which has fat. Whole grains can go rancid, too, but they last a longer period of time because they aren’t ground, which exposes them to oxygen.

  • Oils, such as extra-virgin olive oil, vegetable oil, sesame oil, nut oils, and canola oil. Fish oil supplements can go rancid, too. 

  • Solid fats, like shortening, lard, and butter.

  • Seed and nut pastes, such as peanut butter and tahini.

  • High-fat processed snacks, such as potato chips, shortbread cookies, and crackers. These items are never sitting around my house for long! But if they are old or were improperly stored, they can go rancid. 



How to keep foods from going rancid

Once you know what foods go rancid, take steps to keep them smelling and tasting great. Light, heat, and oxygen all trigger rancidity. Keep those to a minimum and be on your way to fresher, healthier food.

  • Keep food out of the light. Keep cooking fats in a cupboard, or buy them in tins or dark glass bottles, which protect them from light.

  • Store foods in a cool spot. For most shelf-stable foods, cool room temperature works fine. Do you keep a bottle of oil right by the stove? It’s handy, but makes prime conditions for rancidity. Keep your most-used cooking oils in a nearby cupboard instead.

  • Store in the refrigerator or freezer. Some oils, like sesame, walnut, and safflower oil, keep better in the refrigerator — especially if you don’t use them often. Stash nuts, seeds, and whole-grain flours in the freezer in a zip-top bag to last longer.

  • Buy smaller amounts of food you cook infrequently. If you only use, say, whole-wheat flour from time to time, buy a smaller bag. Foods in smaller packages cost more per ounce, but this way you won’t be wasting any.

  • Have just one jar or bottle open at a time. Unopened foods resist oxidation of fat and last longer because they’re not exposed to oxygen.

  • Shop at a store with a high turnover. Food (especially oils and nuts) can go rancid while it’s sitting on the shelf at the store. If you know a food can go rancid, make a point of buying it from a store where those items are restocked frequently, and avoid stores with dusty shelves. If you buy food only to open it up at home and discover it’s rancid, return it. 

  • Grind fresh. Grind seeds, nuts, and flours fresh if you can (see tips in the recipe section below). 

  • Don’t reuse cooking oil. Heat breaks down the structure of fat, and any oil that’s been used once goes rancid very quickly. Frying in a cast-iron skillet is great, but iron accelerates rancidity, so in that case especially, dispose of the oil after you’re done frying.



Recipes for healthy nuts, oils, whole grains, and seeds

Here are more tips for storing and cooking with ingredients so they’re fresh and nutritious 


How to Make Homemade Flour 

Did you know you can make your own whole grain flours on demand using a high-speed blender? Freshly milled flours retain more of their nutrients. Food processors are good for grains like oats and quinoa, but for rice and wheat, high-speed blenders work best.


Vegan Oatmeal Raisin Cookies

Yummly Original

These wholesome cookies contain ground flaxseed, which is especially vulnerable to rancidity. If you have an electric grinder, grind flaxseed fresh and keep extras in the refrigerator; use within a week or two. 


Pecan Crusted Fried Okra

Yummly Original

Heat greatly reduces the stability of cooking fat, so when you reuse frying oil, it can go rancid fast. It’s best to dispose of vegetable oil after frying. If you strain it and re-use it, refrigerate it and use within two weeks.


Homemade Sunflower Seed Butter

Sunflower seeds are prone to rancidity. If you buy them in bulk, give the bin a sniff first, and keep the seeds in the freezer. Once you grind them into sweet, creamy butter in your food processor, it will stay good in the refrigerator for 2-3 weeks. 


Infused Olive Oil

There’s a flaw in this recipe. Can you catch it? It calls for gently heating the oil with aromatics, such as herbs or dried chilies, and then storing at room temperature. Under normal circumstances, an open bottle of olive oil is best stored at room temperature in a cool, dark place, where it can last 3 months or more. But once oil is heated, it’s apt to go rancid. You’d want to refrigerate this infused oil and use it in a month.



More healthy tips

Find more smart ways to get healthy ingredients in your everyday meals with these tips and recipes: 


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