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I generally buy large containers of oil (olive, canola, peanut, etc.) and just refill a handful of smaller oil bottles. That way it's cheaper in the long run, and the smaller bottles are easier to deal with.

I generally just add more oil when a bottle starts getting low. I imagine this could have some bad effects:

  • Oil remaining in bottle could go rancid (though it's getting diluted each time, so I imagine very little remains over time)
  • If any bacteria/contaminants get it, they'll just remain in there forever.

Are these realistic concerns? Are there things that could start growing in pure oil? Would it be worth the hassle to periodically let the bottles run empty and wash them out / replace them?

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2 Answers 2

up vote 6 down vote accepted

Yes these are realistic concerns.

  • the tiniest amount of rancid oil can make your dish taste bad.
  • mold can grow on fat (e.g. penicillium in cheese).
  • oil only has residual amount of water, so it will not accelerate most bacterial growth.
  • shelf life for oil is about 6 months to a year in a dark cool cupboard
  • shelf life is about a year and more in fridge (but the oil clouds and solidifies).

my suggestion would be that when your container is empty, just wash it with a natural degreaser (e.g. vinegar) instead of topping it off. Or top it off, but wash the smaller bottles every 6 months.

UPDATE

Be very careful about what kind of oil you use, in particular if it is not commercial-grade. In this other question you will see that oil or other canned products that provide anaerobic environment (=without oxygen) can be good conditions for some bacteria. Some of them are specifically bad. See also the wiki page for the C. Botulinum for an example.

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Shelf life heavily depends on type of oil and the far end of the range is more like three years. Otherwise great answer! –  sarge_smith Mar 9 '13 at 8:18
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Also, if you use all of it before you refill, the rancidity really won't be a problem; as the OP says, it'll be very diluted, so you'll only get a tiny fraction of a tiny bit of rancid oil even if it's had time to go rancid. So if it's a long-lasting oil (as sarge_smith mentions), you'll be able to go few cycles, a really long time, with no problem. –  Jefromi Mar 10 '13 at 23:25

Yes, they're realistic concerns, but you can also take precautions against rancidity and such.

  1. Keep the oil out of the light. Either use an opaque oil dispensor (mine's stainless steel), or keep it in a cabinet (which my mom does).

  2. Keep the oil away from heat. Don't keep it near the stove or on the window sill.

  3. Don't put anything other than pure oil in the container. (no herbs, garlic, or other infused oils)

My mom would go through a 3L can pouring it into a smaller olive oil bottle she was reusing. I don't recall her ever cleaning it. I do occassionally clean my container, mostly because I keep it out, and after a bit of frying, you get that film on the can, so when it's low I'll drain the remaining oil into my oil sprayer and wash it ... but maybe only 2 or 3 times a year.

The containers I generally mostly empty before refilling ... except for the sprayer. There's a minimim amount required in it so that it'll work, so I just refill it. And I can't remember ever cleaning out the ones I have, other than the sprayer portion when it starts acting up. (I'm on my third one in maybe 14 years?)

I've never had any problems with mold, but I use my containers regularly, and I've only lived for long periods in a moderate climate (Kentucky, Maryland, Netherlands)

update : I should also add ... if you wash the container, it is critically important that it be fully dried before you use it again. Botulism needs moisture to thrive, so you want to make sure that no water is in there. (I suspect that the mold on cheese actually requires the moisture from the milk, not just the fat.) Remember that the French packed meats in fat to preserve them (duck confit & pâté)

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