How long and how should oil be stored?

[Incitatus]

I used some peanut oil to deep fry some meatballs. Should I filter it and store it in the fridge or maybe freezer to use again later and for how long?

[NYC_SKP]

1. I don't think you want to freeze it.

Different oils (canola, peanut, safflower) have different shelf lives but all will go rancid within a year.

Keep in a cool and dark place, but it doesn't need to be refrigerated (though that's ok).

Strain it through some cheesecloth if it's got particles.

If overheated, where it's changed color or started to smoke, toss it.

[Incitatus]

2. Thanks.

I've never considered frying meatballs like that, but I say an episode of Restaurant Impossible recently and that was one of the items shown. I found a recipe online and they were delicious.

[Warpy]

3. In summer here in the desert, everything but olive oil seems to go rancid in a week

if I have it opened and leave it out at room temperature. Sealed, it doesn't make a difference. I've learned to keep my safflower or peanut oil in the fridge in summer.

In winter, my kitchen stays under 60, so I can leave the bottle of oil out for a while.

The freezer won't do much more than the fridge as far as keeping it goes. It will make it solidify nicely, though.

[Major Nikon]

4. Once cooking oil has been used, it is much more susceptable to rancidity

You should be filtering it and reusing it over a short period of time.

Susceptibility to rancidity is directly proportional to exposure to air, light, temperature, and time. Less of each protects against rancidity.

[sinkingfeeling]

5. I put all opened oils in my fridge.

[Major Nikon]

7. Some are much more susceptible to rancidity than others

I don't keep any oils in my refrigerator except for those I pay a lot of money for and want to keep over long periods. For everything else I buy in smaller quantities that I intend on using over a relatively short period.

Most of what I use is olive oil, both EVOO and light. Olive oil stores quite well at room temperature because it has a high monounsaturated fat content. This is also true of Canola oil to a lesser extend due to a lower monounsaturated content (although still quite high relative to most other vegetable oils). Walnut, grapeseed, safflower, coconut, and cottonseed oil all have low monounsaturated levels and do not store well. Omega 3 & 6 oils are some of the most volatile.

If you want to store any oil, it's best to do so out of the light and in a cool environment (refrigerator is not a bad idea). Some oils actually fare worse in the refrigerator, but not many. EVOO is one example.

You also want to be careful about aerating the oil as little as possible and store in containers that are as full as possible and sealed.

[rdharma]

6. As a "newbee" at deep frying, I had the same question. Here's the answer I found at Columbia Health

They address the subject from a health and safety POV.......................

Although re-using cooking oil and/or grease is a somewhat common practice, it can pose some serious health hazards. The most common danger when recycling cooking oil is that it becomes rancid or spoiled. In addition to having strange flavors and odors, rancid oil may contain possibly carcinogenic free radicals (read Antioxidants from the Go Ask Alice! archives to find out more about free radicals). These pesky molecules are then absorbed into the fried food and ingested by an unlucky eater.

Using fresh oil every time you cook is the healthiest option. However, if that is not a viable option and it must be re-used, here are some helpful (and healthful) tips:
• Strain it through a few layers of cheesecloth to catch any food particles before storing. Be careful with hot oil, though, because you can easily get burned.
• Shake off excess batter from food before frying it.
• Use a good thermometer to fry foods at a maximum of 375°F (or 190°C).
• Turn off the heat after you are done cooking. Exposing oil to prolonged heat accelerates rancidity.
• Don't mix different types of oil.
• Store oil in a cool, dark place.
• Avoid iron or copper pots or pans for frying oil that is to be reused. These metals also accelerate rancidity.

Here’s another tip on oil safety. Frying foods at or above 375°F can lead to the accumulation of 4-hydroxy-2-trans-nonenal (HNE) in the oil. What’s that, you ask? HNE is a toxic substance that has been associated with an increased risk of stroke, atherosclerosis, elevated levels of LDL cholesterol (the "bad" cholesterol), Alzheimer's, Parkinson's, and various liver diseases. It only takes one use to create HNE in the oil, and reusing oil at too high of a heat can cause even more HNE to build-up.

How to avoid HNE? When heating oil to very high temperatures, use a thermometer to ensure that you’re not heating the oil above 375°F. This is the ideal temperature for frying. Also, stick to oil low in linoleic acid, such as olive oil and canola oil. Researchers found that HNE is more likely to build up in oils with high levels of linoleic acid. Oils with the highest percentage of linoleic acid are safflower oil, grape seed oil, sunflower oil, and corn oil, so you may want to stay away from those if you enjoy a deep fryer.

http://goaskalice.columbia.edu/reusing-cooking-oil-safe

[demigoddess]

8. oils in the bottle also react to light,

so I always keep mine in the dark pantry or cupboard. No problem with heat here.

[shireen]

9. oil used for seasoning and storing iron-cast cookware

What about storage of cast iron pans? I've heard that it should be lightly oiled before storage. Wouldn't that layer of oil become rancid and affect the taste of food?

cast iron pans have always confused and intimidated me.

[Major Nikon]

10. Eventually, yes

If you know you are going to store them long term, you can coat them with food grade mineral oil which will not go rancid, then wash it off before use. I coat mine with light olive oil which will last a long time. After washing, make sure you dry them thoroughly before storage, apply a light coat of oil, and if you store other pans and/or lids on top of each other, separate them with a paper towel.