Quick Answers
Oil can go rancid over time. Some signs that oil has spoiled include:
- Changes in color – Oil may turn darker or cloudy
- Changes in smell – Rancid oil smells off, bitter or unpleasant
- Changes in texture – Oil may become thicker or stickier
- Smoke point changes – Oil smokes at a lower temperature than when fresh
Oils with higher saturated fat contents like coconut oil tend to have longer shelf lives than oils high in polyunsaturated fats like vegetable and nut oils. Storing oil in a cool, dark place in an airtight container can help extend its shelf life. Refrigerating oil after opening may prolong freshness. In general, unopened oils can last 6-12 months while opened oils may start spoiling after 3-6 months.
How to Tell if Different Oils Have Gone Bad
The signs of spoiled oil and how long oil lasts depend partly on the type of oil. Here is more on how to tell if common cooking oils are still good or have gone rancid:
Olive Oil
Signs of Spoilage:
- Color changes from green to yellow, orange or brown
- Cloudy appearance
- Bitter flavor
- Unpleasant, rancid smell
Shelf Life:
Unopened olive oil lasts 12-24 months past the sell by date. Opened olive oil lasts 3-6 months.
Coconut Oil
Signs of Spoilage:
- Color changes from white to yellow or grayish
- Strong rancid odor
- Texture changes from solid to liquid at room temperature
Shelf Life:
Unopened coconut oil lasts 12-18 months past the sell by date. Opened coconut oil lasts 6-12 months.
Vegetable Oil
Signs of Spoilage:
- Darker yellow color
- Cloudy appearance
- Unpleasant, rancid smell
- Bitter, soap-like flavor
Shelf Life:
Unopened vegetable oil lasts 6-12 months past the sell by date. Opened vegetable oil lasts 3-6 months.
Nut Oils
Signs of Spoilage:
- Color changes from pale to yellow, brown or orange
- Nutty aroma turns stale, bitter or rancid
- Thickness increases, oil feels sticky
Shelf Life:
Unopened nut oils last 6-10 months past the sell by date. Opened nut oils last 3-6 months.
Canola Oil
Signs of Spoilage:
- Changes from light yellow to dark yellow or orange color
- Cloudy appearance
- Strong, bitter, unpleasant odor
- Unpleasant taste
Shelf Life:
Unopened canola oil lasts up to 12 months past the sell by date. Opened canola oil lasts 6-12 months.
Corn Oil
Signs of Spoilage:
- Darkens in color
- Cloudy appearance
- Strong rancid smell
- Bitter, unpleasant taste
Shelf Life:
Unopened corn oil lasts 9-12 months past the sell by date. Opened corn oil lasts 4-6 months.
Avocado Oil
Signs of Spoilage:
- Changes from green to brown, yellow or murky color
- Nutty aroma turns rancid
- Thick, gluey texture
Shelf Life:
Unopened avocado oil lasts 6-12 months past the sell by date. Opened avocado oil lasts 3-6 months.
Grapeseed Oil
Signs of Spoilage:
- Color changes from pale yellow to darker yellow
- Unpleasant, rancid smell
- Bitter, unpleasant taste
Shelf Life:
Unopened grapeseed oil lasts 12-14 months past the sell by date. Opened grapeseed oil lasts 4-6 months.
Sesame Oil
Signs of Spoilage:
- Darkens significantly in color
- Strong bitter, rancid odor
- Unpleasant bitter taste
Shelf Life:
Unopened sesame oil lasts 6-12 months past the sell by date. Opened sesame oil lasts 3-6 months.
Flaxseed Oil
Signs of Spoilage:
- Color changes from golden to brownish
- Nutty aroma turns rancid
- Oil feels thick and sticky
Shelf Life:
Unopened flaxseed oil lasts 4-6 months past the sell by date. Opened flaxseed oil lasts 2-3 months.
How to Store Oil Properly
Proper storage can help extend the shelf life of oils. Here are some tips for storing oil:
- Purchase oil in opaque, air-tight containers – Light and air cause oil to spoil faster
- Keep oil in a cool, dark place – Store away from heat, light sources and windows
- Refrigerate oil after opening – Colder temps slow spoilage
- Make sure bottles are sealed tightly after use
- Use clean utensils when dispensing oil
- Don’t let oil sit at room temp longer than necessary
- Use oil within recommended time after opening
Oils stored properly in the refrigerator can last up to 6 months or longer after opening. Counter-top storage reduces shelf life after opening to about 1-3 months. Keeping oil next to the stove or routinely exposing it to heat and light will cause it to spoil rapidly.
How to Tell if Oil Has Gone Rancid
Rancidity is the main way oil spoils. Oils contain fats that can oxidize and degrade over time, especially when exposed to heat, air and light. Here are tips for detecting rancid oil:
Check the Smell
Fresh oil has a neutral aroma or a slight nutty or grassy scent depending on the type. Rancid oil smells stale, bitter, unpleasant or like chemicals. A sour, fermented odor is a sign oil has turned.
Check the Taste
A small taste test can confirm rancidity. Place a drop of oil on your fingertip and taste it. Rancid oil will taste off, bitter or unpleasant. Spit it out right away if the oil tastes bad – don’t swallow!
Check the Color
Oil naturally darkens somewhat with age. But oil turning much darker than when purchased or developing an orange, brown or yellowish tint can indicate it has spoiled. Cloudiness is also a bad sign.
Check Texture and Consistency
Oil may thicken and turn sticky or syrupy as it spoils. When warm, rancid oil is also thinner and flows more quickly than fresh oil.
Check Smoke Point
The temperature when oil starts smoking is its smoke point. As oil degrades, its smoke point lowers. If your oil smokes at a temperature much below normal, it could be rancid.
Here are typical smoke points for fresh vs. rancid oil:
| Oil Type | Fresh Smoke Point (F) | Rancid Smoke Point (F) |
|---|---|---|
| Extra virgin olive oil | 375-405 | Less than 375 |
| Vegetable oil | 450-470 | Less than 450 |
| Coconut oil | 350 | Less than 350 |
| Peanut oil | 450-485 | Less than 450 |
| Grapeseed oil | 420-445 | Less than 420 |
Health Risks of Consuming Rancid Oil
Eating rancid oil poses some potential health risks:
- Food poisoning – Rancid oils can harbor harmful bacteria that cause foodborne illness.
- Free radical damage – The oxidized fats in rancid oil are pro-inflammatory and create free radicals that can damage cells.
- Decreased vitamin and antioxidant levels – Spoiled oils lose nutritive value and antioxidants that go rancid.
- Gastrointestinal distress – Stomach pain, cramping, nausea and diarrhea from eating rancid oil is common.
- Allergic reactions – Rancid fats can trigger food allergies and sensitivity in some people.
While not acutely toxic, the cumulative effects of consuming oxidized lipids may increase disease risk. The foul taste of rancid oil limits intake of large doses. But to avoid adverse effects, it’s safest not to eat any oil you suspect has spoiled.
How to Use Up Oil Before It Spoils
To avoid wasting oil or having it go bad before finishing the bottle, here are tips for using opened oil quicker:
- Use more oil for sautéing veggies, eggs, stir-fries etc.
- Make dressings and dips using oil like ranch, green goddess, aioli
- Brush oil on meat and fish before baking or grilling
- Fry fish, chicken, fritters and other breaded items
- Make baked goods like cakes, muffins and cornbread with oil
- Use it for making granola bars, energy bites and snack recipes
- Try oil-based sauces like pesto or chimichurri to top meats, fish, veggies
- Brush on crusty bread and toast in oven or air fryer
- Grease pans liberally when cooking meats, roasting veggies etc.
- Preserve or marinate vegetables, meats and cheese in oil
Getting creative with recipes and techniques for working through open bottles keeps oil from going to waste. The key is consistently using the oil so it doesn’t sit neglected for long periods.
Conclusion
Oil eventually goes rancid from oxidation and improper storage. Telltale signs of spoiled oil include unpleasant odors, changed consistency, altered color and bad taste. Some basic tips like refrigerating after opening, keeping oil in dark bottles and checking for signs of rancidity can help you avoid consuming rancid oil and identify when it’s time to throw it out. With proper care and handling, oils can retain freshness and flavor for months past their “best before” dates. But once an oil shows signs it has turned, it’s safest not to take risks and to discard it.
