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I found this:

enter image description here enter image description here

The bottle has a best by date of 2022 and was opened a few months ago.

Is that common that mold can grow in vinegar?

Thomas
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4 Answers4

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Normal vinegar concentration (usually around 5% acetic acid) is too acidic to grow mold in the vinegar itself. Mold can sometimes grow on the bottle or on the surface of the vinegar. It isn't dangerous and can be wiped/skimmed off.

What you are seeing is called the mother.

enter image description here

Vinegar is produce when acetobacter bacteria consume alcohol and produce acetic acid. The bacteria form a culture as they work. In the case of filtered vinegar, this culture is removed before bottling but letting a bottle of unpasteurized vinegar sit for a while will allow the culture to reform. Unfiltered vinegar often already has some of the mother present.

It is harmless and can be used to start your own vinegar if you have stale wine sitting around.

Sobachatina
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    what I have looks very similar to that photo; The vinegar is a supermarket item, do they sell them unfiltered (like a Trappist beer for example)? Does that also mean that what is on the top of the bottle is not mold? it looks white and hairy – Thomas Sep 17 '18 at 15:05
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    Mold can grow at the surface of the vinegar and on the bottle. Everything I've read is that it's harmless and you can just wipe it off. Undistilled, unpasteurized, vinegar of any kind can eventually form a mother. Unfiltered vinegar may already have some of the mother in the bottle. Added to answer. – Sobachatina Sep 17 '18 at 15:09
  • ok, great! I was a bit scared seeing it for the first time, knowing I used that vinegar a lot! – Thomas Sep 17 '18 at 15:13
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    Anecdotal, but it seems to me that balsamic seems to get the splatter molds a bit more frequently. I believe the spatter molds can form because the acid level can drop do to exposure to air, dust, etc and allow them to form. Wiping should clean it, and then the higher acid when you pour again should kill spores. That is should. Safest it wipe after use so it does not happen, but no, I do not remember to either. – dlb Sep 17 '18 at 16:18
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    From DrMoishe Pippik on chemistry.SE: "Vinegar itself can be metabolized by microorganisms. According to the Compendium of the Microbiological Spoilage of Foods and Beverages, 'several molds, yeast and bacteria are capable of spoiling vinegar... [such as the appropriately named] Lactobacillus acetotolerans. ' " – Keith McClary Sep 19 '18 at 02:25
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    @keithmcclary- that is interesting. I'll be sure to couch my descriptions in some less absolute modifiers next time. Of course, for the purposes of cooking, the shelf life of vinegar is essentially indefinite. – Sobachatina Sep 19 '18 at 03:39
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I see that people are calling this a "vinegar mother," but for anyone who sees this post in the future, this is most definitely mold. There is a mother at the bottom of Thomas' bottle, but those are hyphae coming out the top of the vinegar bottle. (And in the genuinely harrowing image submitted by C. Barry, it would seem the mold is either fruiting, sending its mycelium high up to search for oxygen, or more likely both based on the coloration - which is likely spores forming - and the unusual height of the mycelium.)

Plenty of fungi like/need acetic acid, and since balsamic is so sugary, I'm guessing it made a perfect home for some mold. Acetic acid at 5% isn't enough to totally prevent mold from forming, it's just very helpful for inhibition of mold growth. You can still get molds on occasion. (See for yourself!)

The mother of vinegar mentioned in the other post is the pellicle that's often formed during vinegar fermentation. It should be a rubbery, wet, cellulose disc, and that's what it looks like at the bottom of the bottle. The fuzzy stuff growing at the top is not that, however; it is definitely mold. A thin biofilm could just be kahm yeast, but in vinegar, fuzz = mold. Some vinegar fermenters will tell you that you can just skim the mold off the top, but this is not true. By the time you see a fruitbody or visible mycelium, that fungus has already made a bunch of byproducts (usually called mycotoxins) that are potentially very harmful to you and dropped them directly into the vinegar. Technically, there's a chance that you got one of the food safe molds and are fine eating it, but I wouldn't take the chance if I were you. There's a reason we don't talk about food safe molds very often.

Jonah French-Jurgens
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enter image description here I was surprised to find mold growing on balsamic vinegar. Maybe it's because the top was not screwed on tightly.

C. Barry
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Balsamic vinegar contains sugar. Sometimes a lot of sugar. The mold you are seeing is probably related to that, and would be very unlikely to happen on regular vinegar.