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A question about cooking oil bottle caps

  1. Mar 29, 2009 #1


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    Gold Member

    Hi PF,
    I really didn't know where to ask the following question so redirect the thread if necessary.
    I'd like to know why I can't really "close" cooking oil bottle caps. I can screw the oil bottle caps but when it's almost totally screwed, suddenly it's like it unscrew and I have to screw it again and stop just before it unscrew.
    It happens with any brand of cooking oils so there's a good reason to use this kind of bottle caps. Until now I don't really have any idea about the reason it is so. If you know it feel free to explain it to me.
    Thank you.
  2. jcsd
  3. Mar 29, 2009 #2


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    Staff Emeritus
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    I was trying to figure out why one was wanting to cook bottle caps.

    I think the problem of overtightening plastic bottle caps, or rather cap with polyethylene threads is not uncommon. Simply don't overtighten them.

    I have an olive oil bottle with a polyethylene insert in the mouth of the glass bottle and an insert in the metal bottle cap. The polythylene insert in the cap seals with the insert in the mouth of the bottle, but the threads of the metal cap screw into the thread of the glass bottle.

    I think the choice is based on the desire to have a material that doesn't react with the cooking (e.g. olive oil). Why a particularly brand doesn't use a harder plastic is not clear.

    Perhaps it's a matter that some designs are better than others.
  4. Mar 29, 2009 #3


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    Likely it's because of a metal screw top on a glass bottle. The oil is a lubricant so that allows you to continue to tighten and the ribs in the bottle cap to slip over more easily the glass ridges in the bottle. I don't think there is anything intentional about it, just that the oil likely makes it feel easier to bump over the ridges.
  5. Mar 29, 2009 #4


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    The inserts - 1 in the cap and 1 in the bottle - I think are to create a better air seal so the oxidation of the oil or whatever makes the oil go south after a time is minimized. Maybe even for the very reason that the caps are easy to over-tighten (albeit with less torque than with other things) and jump the threads.
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