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I have noticed that when I open a jar of olives (we eat a lot) sometimes some mould starts to grow on the surface of the top layer of olives floating at the top of the brine and there is mould on the brine. This only happens on the few rare occasions that we open a jar then don't touch it for a few weeks.

I have a biology degree and some knowledge of microbiology; we only use clean forks or spoons to remove the olives and I'm sure it's not oil congealing at the top.

I recently bought a large catering tin of olives because we eat a lot of them; so it will work out cheaper this way if I can decant them into jars. But I'm worried that in the process of decanting into the jars, airborne microbes will enter and spoil the olives. I am assuming there is something I can add to them but I'm not sure. I don't think I want to heat them as they are already prepared and ready to consume.

I've never done any preserving or anything but someone told me campden tablets can be added to stop the mould growth. Is this right? If so how much should I add?

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  • Do you (or others in the household) stick your fingers in the jar to remove olives?
    – moscafj
    Commented Sep 27 at 18:36
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    Are you sure that it is mold, and not small bits of fat floating to the top and congealing?
    – Debbie M.
    Commented Sep 27 at 20:43
  • to answer moscafj no we never stick fingers in at all ever. we use a clean fork or spoon to remove. I know about microbiology from my degree and have taught everyone what they need to know, so the family are aware of these issues. the mould comes from airborne spores. I am asking for ways to treat this by addition of something like campden tablets that are added to wine or something like that.
    – VeronicaBee
    Commented Sep 28 at 8:43
  • to answer debbie yes I am very sure. I have a biology degree and some knowledge of microbiology so the question I as asking is very specific. What can I add to the olives when I decant to reduce mould growth. I should have made my question more specific I guess. Maybe I should edit or repost it worded better. I did it in a bit of a hurry so my mistake there entirely.
    – VeronicaBee
    Commented Sep 28 at 8:45
  • I can't figure out how to directly answer specific questions posted to me as I'm a new user so I apologise if I'm all over the place
    – VeronicaBee
    Commented Sep 28 at 8:46

3 Answers 3

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Decanting to sterilized jars, in very clean conditions, maybe with gloves, would probably do the trick in and of itself. I doubt you would introduce mold spores if you worked quickly and cleanly. However, if you wanted an additive, sodium benzoate or potassium sorbate are both used in the food industry to prevent fungal and yeast growth. .025% to .1% by weight seems to be the recommendation I find on the web. It is quite possible that the olives you have purchased already have these additions.

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  • Thank you moscafj. That's very helpful. I will check the ingredients on the tin and see what it contains.
    – VeronicaBee
    Commented Sep 28 at 17:17
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One possibility, which might be irrelevant depending on what you do now, is to store the aliquoted jars in your fridge. The cold should slow growth of most mould species fairly well.

A further option is to remove the brine and freeze the olives in bags, defrosting as needed. The salt in the brine and oil in the olives should prevent them freezing completely and going to mush on thawing.

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    I was planning to store aliquoted (haven't heard that word since my DNA lab days) jars in the fridge yes. I would be worried that freezing would sufficient change the molecular structure for it to be detectable in terms of a change in texture (I tend to dislike pre frozen food because of this issue) but I think it's worth trying that as an experiment...
    – VeronicaBee
    Commented Oct 2 at 9:41
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I would just add a thin layer of olive oil on top to prevent air contact with the olives. Some salt could also help.

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  • I like this idea
    – VeronicaBee
    Commented Oct 2 at 9:42

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