Vinegar in the dark

[gatewood]

I put my vinegar fermenting vessels inside black, opaque bags because I've read that, mother of vinegar must be placed away from light sources, for it to effectively ferment alcohol into acetic acid.

So I have 2 questions because I never knew why:

1. Why is that?
2. What happens to acetobacter when exposed to light?

 

[RPh_Guy]

UV light damages cells by breaking apart DNA/RNA. It's why you get sunburn and skin cancer.

I suggest to just cover it loosely with foil.

 

[ten80]

UVb light that causes visible sunburn doesn't pass through glass, so perhaps not the best analogy since there's also UVa to content with. Acetobacter are particularly sensitive to the blue-indigo-violet UVa end of the light spectrum of which about 37% passes through glass, so keeping a clear jar out of direct sunlight or a decent distance from incandescent or fluorescent bulbs is best practice. Using a brown growler would be sufficient in most cases, as is supported by the results of a famous vinegar and light experiment by Tolomei conducted in 1891. You can find a more recent explanation of his experiment here: https://supremevinegar.com/2018/06/21/the-deal-on-light-and-vinegar-and-kombucha-fermentation/

I make vinegar in brown growlers stored in my laundry room which usually only has indirect light passing through light fabric blinds. I don't have any issues unless the vinegar mother is a dud.