How to reboil the oil?
February 2, 2011 6:36 PM   Subscribe

How can I safely reuse cooking oil?

This thread has a couple of biochemists weighing in that the reusing of cooking oil can be safe. However, I would like to know:

1. How do I go about doing this? An answer to that previous thread mention straining the used oil with a coffee filter. The others are less specific. Is the coffee filter the best way to do this? It seems like it could be pretty time-consuming and messy.

2. Is it OK to store the oil in a coffee can at room temperature if I don't have the container the oil came in? Or does it need to be in an airtight jar?

3. Generally, how many times can I reuse it? There's advice about it darkening, but I'm not great at know when dark is too dark.

I usually have oil or grease that I feel bad about throwing out after frying chicken or making bacon, if that affects matters.
posted by ignignokt to Food & Drink (15 answers total) 4 users marked this as a favorite
As I understand it, straining the oil is not for health or safety reasons, but just to get "bits" out, and prevent flavour contamination. So it doesn't matter if you don't strain it, and it certainly doesn't matter if you do it through something coarser than a coffee filter (like a sieve, for instance).

After all, pate and similar things are traditionally just sealed with a layer of lard or whatever on top, which preserves them sufficiently. So bits of meat or whatever suspended in your oil will be preserved perfectly well.

I reuse oil until things start to taste unpleasant when they come out. Darkness is a matter of personal taste.

If I were going to store oil at room temperature, I would do it in a dark or opaque container, and seal it. But I doubt that not being perfectly air-tight will affect it much - see again, oil and fat as preservative.
posted by lollusc at 6:46 PM on February 2, 2011

You need to be more specific than "the oil" - coconut oil is stable at room temperature. Vegetable oil goes rancid comparatively quickly. Olive oil; somewhere in the middle.

Cheese cloth strains more quickly than a coffee filter and catches most of the same chunks.
posted by carlh at 6:46 PM on February 2, 2011

After frying, I usually pour most of the oil through a cheesecloth or fine wire-mesh strainer; when it gets to the bit of oil with crud in it, at the bottom, I put it through the coffee filter. So the coffee-filter part only applies to the last cup or two. After the straining, I just store it in a glass bottle or jar, and store it in the back of the fridge. I reuse it about three to five times; after that, I find it starts accumulating vaguely-undesirable off-flavors.

As for rendered bacon-fat: pour it, save it! Keep it in the freezer until it's time to make confit, and then use it to add a wonderful undertone of baconry to beef or pork lamb.

Note: I am not a biochemist, and these rules mainly apply to taste and frugality rather than maximum health benefits.
posted by Greg Nog at 6:53 PM on February 2, 2011

Although I never reuse cooking oil, I always save the grease from bacon. I pour it into a small lidded container and keep it in the refrigerator, then use a tablespoon or two to brown onions or stew beef. I purposefully don't strain it, since tiny fragments of bacon add flavor, though they can burn if the heat is high enough.

Bacon fat is not as unhealthy as it sounds. It contains significantly less saturated fat than butter.

Bacon fat will stay good at room temperature for a good while, much longer than polyunsaturated vegetable oil will, but it's liquid most of the time in our climate, and makes a horrible mess if someone knocks it over, so it's safer for me to keep it in the fridge.
posted by Ery at 6:57 PM on February 2, 2011

How well the oil taste the next time you use it really depends on how hot you've heated it this time around. I use a paper coffee filter (in a wire spider) for frying oil, but if it's animal fat (which is gooey solid at room temperature) I just a fine sieve.

Fry oil is usually good for 3 fries if you don't overheat. After that it's just too dark and bitter. It'll smell a bit bitter too. It all really depends on the smoke point of your oil. If you keep way under the smoke point, you can reuse the oil more.

I keep the oil in spaghetti sauce jars in the fridge.
posted by Sallysings at 8:08 PM on February 2, 2011

Awesome, I had no idea that fat could preserve meat! Or of the benefits of bacon fat.

So, the oil I usually use to deep fry is peanut oil or olive oil. Sounds like keeping it in the fridge is a good way to hedge my bets.
posted by ignignokt at 8:11 PM on February 2, 2011

Oil goes rancid because it oxidizes, so the longer you're going to go between uses, the more you're going to want to minimize head space (less oxygen equals less oxidation) and keep it in a cool place (cooler temperatures reduce the rate of reaction). A coffee can isn't going to be ideal, but assuming you still have the plastic lid (and let the oil come down to a reasonable temperature before you put it on the can), it will do.
posted by Kid Charlemagne at 8:11 PM on February 2, 2011

I wouldn't reuse canola oil; the omega-3 alpha-linoleic acid is highly unstable and will oxidize very easily, if it isn't already oxidized when you get it.

Although, I wouldn't use "vegetable" oils at all.
posted by Earl the Polliwog at 8:41 PM on February 2, 2011 [1 favorite]

Bacon fat is traditionally saved in your fridge in a coffee can after straining. This is why they issue you that can when you move South of the Mason Dixon line.
posted by immlass at 9:04 PM on February 2, 2011

I reuse canola oil all the time, no rancidity problems.

Tea strainer/small metal mesh stainer works just fine for me for removing bits. Strain into a glass jar or for smaller amounts, into just a small ceramic bowl. Plop a plastic can lid over it to keep stuff from falling in it. I rarely reuse the same oil for more than 2 or 3 days straight.

I've also re-used big batches of canola used for tempura. Strained into a glass jar with a lid. Lasted a couple of weeks; zero problems with it going rancid.

Bacon fat is awesome - if you're frying stuff with it (or 50/50 mix of bacon fat and a vegetable oil), it comes out so much more fluffy and "tender" than pure vegetable oil. Perogies? Completely different experience.
posted by porpoise at 9:49 PM on February 2, 2011

I render bacon, beef bone marrow (I buy a bag of soup bones to make stock and half have good marrow), and chicken skin. These are strained, put into an ice tray to be frozen, and then thrown into a ziplock bag to keep in the freezer. Steak cooked with marrow turns out like the best marbled beef you've ever had.
posted by JackarypQQ at 11:35 PM on February 2, 2011 [1 favorite]

I do filter my oil through coffee filters to reduce the amount that it smokes when I reuse it. If you get the #2 filters, they fit pretty well in a funnel, and then you can just pour some oil in there and let it drip through. When the filter gets a bit gunky, I put in a new one so that the oil filters faster. And I do the whole process in the sink, because I invariably spill a little oil somewhere and I'd rather spill it in the sink than anywhere else. At the end, I put the cap back on the oil bottle and wash the outside with hot water.

Also, the rule I've always heard is that you should mix used oil half and half with fresh to reduce smoking and I've found that to be very helpful.

As for saving and reusing bacon fat, well, I would ask your cardiologist about that.
posted by WorkingMyWayHome at 9:05 PM on February 3, 2011

Thanks, guys, chicken frying day is tomorrow! And I'll be well-equipped to not be as wasteful the next time.

Also, I had no idea marrow was a thing that could be good. I don't get beef with bones very often, but the next time I do, I'll try to save them.
posted by ignignokt at 9:50 PM on February 3, 2011

Ah, chicken fat. It's not one of the better flavoured animal fats; depending on how much chicken you fry or how fatty your chicken chunks are, the saved frying oil may take on a stronger than desired taste of chicken fat.

Diluting 1:1 with fresh oil can help ameliorate the flavour if you find that it's too strong.

Roasted Bone Marrow - AKA "Meat Butter." You can also get your butcher to spiral cut (?) beef marrow bones or they'll be able to sell you marrow completely freed from the bone. Lightly dust in flour cut with a little salt and pan fry in butter.
posted by porpoise at 5:31 PM on February 4, 2011

Sorry, that's pipe cut marrow bones.
posted by porpoise at 9:18 PM on February 7, 2011

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