I have some kombucha scoby that I let go way too long (had to leave town for a bit, new job…) and it has gone to vinegar. I would hate to just throw it out as it’s delicious vinegar. I’d like to give out small jars to friends and family. Can I use any regular bottle or even after this long will it keep producing co2? If it’s still pumping gas it needs to be bottled in bottles that can handle it. How can I know if a bottle is safe for bubbly liquids?
I would suggest, for the combination of "possible pressure" and also "easy dispensing and resealing" flip-top bottles (ceramic stopper and rubber washer on a wire bail arrangement) which were (or are intended if you are not re-using) used for a carbonated beverage (examples common in my area are Grolsch beer in green, or sparking lemonade in clear bottles. Brown beer bottles are also seen occasionally.)
I do, in point of fact, use one of these for balsamic vinegar (but that's not actively fermenting, from what I see.)
It is difficult to do it visually, even though there is some correlation between glass thickness and suitability for bubbly liquids. The practically useful way is to go by just knowing what the bottle was intended for.
If you are going to purchase bottles, you might get some that are intended for canning. Weck has some, but the shape is probably not perfect for vinegar, they are rather wide-mouthed. Alternatively, you can reuse bottles which contained a fizzy liquid - fizzy water, soft drink or beer bottles will all be able to withstand some pressure.
The bigger question is, how do you plan to store the liquid? You can cap it for shipping, but once it goes into a cupboard for use, people will want their vinegar to be well-behaved. Having a shower of vinegar every time they open the bottle, and then having to use some complex mechanism to close the bottle, is not pleasant. It is more common to store actively fermenting liquids in a vessel with an escape lock, which removes the danger of spray-on-opening (or the cap shooting out some night), but also has a rather strong smell.
If it were me, I would try to find ways to prevent active fermentation, rather than choosing a strong bottle.
If you are using recycled bottles, I would say you should make sure they are relatively thick, and were originally used to bottle carbonated beverages.
Also, to be on the safe side, when you decide to open the bottle after your kombucha has fermented, place it in the refrigerator overnight to reduce some pressure first; from Fermentation, over-carbonation, and explosions are real:
This particular growler of kombucha was only half full, so I assumed there could only be so much pressure built up and it would be safe to open at room temp (but still done so over the sink).
I couldn't have been more wrong.
I recommend reading the article in the link.