I have a water bottle that the silicone seal/gasket/o ring developed some black mold. I soaked it overnight in undiluted vinegar (I always see it being diluted should I be doing this?) but it still has a black discoloration. Is this stained or evidence that it still has mold? I scrubbed this with a stiff brush and even scraped it with my fingernail and there is nothing on the surface that can be felt. Also, I see all these mixtures of baking powder, water, bleach, vinegar etc and then the option of boiling. If boiling will do the trick why not just boil? Do these other techniques do something that boiling doesn’t? Thanks!

1 Answer 1


This is very likely a mold species.

It is impossible to say if you have killed it by your treatment methods, but the boiling at least should kill any growing mold, but won't affect any spores if they have been produced. Bleach and other chemical methods such as benzalkonium chloride might work against spores, but you would need to ensure that

  1. your seal is chemically compatible (most silicone-ware is very stable and unaffected by many chemicals).
  2. that you use a high-enough concentration.
  3. that you have sufficient penetration of the seal by the chemical - killing surface contamination might not be effective against stuff inside.
  4. (most importantly) that you can wash it out again so that you aren't drinking the chemical.

The black coloration is merely an indicator that you have had the mold there, so it can be dead and still be discoloured. Even if you killed it, the color will still be there as you haven't gotten rid of the actual cause of the discoloration, which is produced by the mold and is unaffected by the killing methods used. Bleaching would be the only method that might take out the color, but even that might still leave some residual color - possibly a brownish or yellow patch left.

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