Do you reuse cooking oil?
I have never done it, but I know that many people do. Are there certain oils that you wouldn't reuse? How many times do you use the same oil? It would seem that the biggest cost benefit is for deep frying, where a lot of oil is used, but do you also reuse oil for pan frying and sauteing?
It depends on the type of oil and what you cook in it. Olive oil turns bitter pretty quickly when heated, especially unflitered oils, so only use those once (although some would say you should never use those oils to cook with in the first place). For deep frying, I use a good quality, high-smoke-point oil like peanut oil 3 or 4 times. If however, I cook fish in the oil, it has to go.
I especially like to reuse oil that I used to fry herbs. For example, I made fried sage leaves the other night. I fried them in a few tablespoons of peanut oil. The oil was infused with the sage flavor and was great to use to sautee.
I was just pondering the oxidation of oil the other day. I was noticing how, in further stages of oxidation, oil will polymerize into glue- and this glue isn't soluble by either water or soap. As it polymerizes further it hardens completely (pan seasoning), but the glue stage seems to have me thinking the most. Is this glue stomach-acid soluble? The warmer it gets the stickier it gets. What's it doing in the body? I know dogs are hardwired to be able to handle polymerized/rancid oils, and humans, being omnivores, in theory, might be able to handle rancid oils. But when I get some of this 'glue' on my hands and can't wash it off with soap and water, I really have to think twice about re-using frying oil.
I don't subscribe to the crackpot idea that polymerized oils are responsible for aging, but I really can't shake the idea that consuming them is probably not the best idea.
I've always tried to live by the adage 'Eat foods that spoil before they spoil.' I think that's applicable as well here. If you want to re-use oil, use a fat that isn't going to break down as easily such as tallow or palm oil.
I reuse the peanut oil in my deep fryer. I strain and refrigerate it between uses, and don't reuse it if I've cooked anything that will flavor it, like fish. But I can get through quite a few batches of french fries before the oil goes off and I need to replace it.
I also strain, boil, refrigerate and reuse the duck and goose fat I use for making confit de canard. Those fats will keep a year or more if properly treated and then chilled.
I never reuse pan-fry or saute oil.
I'll admit to reusing oil under certain conditions.....If I make something and I have not burned anything in the pan,and knowing I will make something later in a similar manner.... then I will let the oil in the pan cool, not wash and use later. Think along the lines of pan frying an egg or sweating onions or for a recipe. It's my small way of trying to be green.