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Nov 18, 2009 06:35 AM

Reusing deep frying oil? What are "the rules"?

I looked for a thread on this topic, but was unable to find one. What are the rules of thumb for saving and reusing deep frying oil? I don't remember the source, but I read once... from a source I apparently trusted... that if oil was used to deep fry protein (i.e., fish, chicken, turkey, chicken fried steak, etc.) it shouldn't be resused. However, if used on non-proteins (potatoes, tortilla chips, tempura veggies, etc.) it can be reused.

That "rule of thumb" makes deep frying turkeys a significantly more expensive proposition, given the price of peanut oil these days. A friend recently told me he has used the same oil for frying his last five turkeys, or so... apparently without any degradation in the quality of the finished product. Given the infrequency of turkey frying occasions, I can't believe the oil didn't go rancid on its own over this length of time.

Can anyone help de-confuse me? How can one determine when the oil is spent, past its prime, or gone rancid? What rules do restaurants use? I would hate to have friends over for deep fried turkey only to find the bird to be "off tasting" after all the preparation, drama and fanfare!

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  1. I have never deep fried turkey. I deep fry very seldom, so I do reuse the oil.

    After my oil has cooled I filter it (coffee filter or cheese cloth), bottle it and put it in the fridge.

    Each time you use the oil it will darken - I only let it get a few shades darker, ie reuse 2-3 times max. I do not use oil from fried fish when frying anything else in order to avoid transfer of flavors.

    If the oil is bad it will be apparent with a quick sniff test or a taste.

    If you want to get rid of a quantity of used oil, post on craigslist or freecycle - there are many people making their own bio-diesel who will be thrilled to pick it up!

    1 Reply
    1. re: meatn3

      The problem with refrigerating oil is when to use it. My mom put a saucepan full of oil on the stove straight from the fridge and as it heated it went up like an automic bomb onto the ceiling. No one got hurt but soooo dangerous! It must be left out till room temperature when using large quantities that are cold.

    2. I asked a similar question a few weeks ago. Here's that thread:

      1. If restaurants actually test it (they should, but not many do) there is a free kit that the fry oil companies give out for free, to show you that oil will be a lot darker than you think before you should dispose. A glass eyedropper to suck it up and a few different tubes of used oil at different stages. I always think mine is a goner because it looks so dark. but when you actually compare there's still a long way to go. The ultimate sign is if it foams up when you put something in the hot oil: then it is well past its prime and you shouldn't use. But that doesn't mean it will make you sick or anything, just that it will taste sort of burnt.

        As far as meat and non-meat in the same fryer, they do that all day long at almost any restaurant you can name. Places that are really picky will dedicate certain fryers for fish, and maybe meat in another, or just french fries if that's an important item to them. Any off tastes occur due to not straining the oil of the debris in the bottom (which comes from breaded foods mostly). It doesn't go bad on its own, just from overuse really. I've seen solid shortening (like Crisco) go rancid, but not liquid.

        1 Reply
        1. The only thing I ever deep fry is turkey at Thanksgiving. I might strain it through a coffee filter in a funnel and use it once more, but I sure won't use it repeatedly. I think trans fats may form over time, for one thing. You're right, though, I use peanut oil and it is pricey to toss it each time.

          Here's a short article I googled up:

          2 Replies
          1. re: mcf

            I think (too lazy to look up) trans fats are put there when the oil is processed, they don't "form over time". Where I live it's against the law to use any oil with transfats anyway, and it's funny how I don't obsess about them anymore, I almost forgot about all the controversy......but anyway peanut oil isn't processed like commercial fry oil and I don't think there are any concerns with transfats there. Feel free to refute though.

            1. re: coll

              Trans fats are formed in some oils by hydrogenation, some natural transfats occur in smaller amounts naturally, but heating causes changes in the oil and undesirable compounds to form also.

              So yes, you can create less healthful oil over time with re-use.

          2. I saw Alton Brown frying a turkey on Good Eats over this past weekend; he said that the oil is good for one more use after the turkey. I've worked in restaurants for years and I can tell you that most use the oil until they can't use it anymore and it's mixed with everything: chicken, fish, breaded veggies, and even donuts at one place I worked in.

            At my most recent job, they change the oil a couple times per week depending on how how much use the fryers get, but they filter it several times during a shift and at the end of the night.

            With that said, why shouldn't we re-use oil at home? It has to be cleaner than any restaurant, right? I cook my chicken and pork with the same oil and strain it after use. I cook my potatoes or veggies in separate oil and the same with fish. I don't mix any of them and store separate. I use them a few times each and discard before it turns brown.