Vinegar

Why Vinegar?

This isn't a hard one: homemade vinegar is very delicious and very easy! Personally, I think it is one of the best and most straightforward ways to get started in fermentation. And you can create countless delicious things that would be very hard to find (or would be very expensive) in a store.

Getting Started

First, grab a bottle of unpasteurized vinegar (Bragg seems to be one of the better and more consistently available brands) from your local grocery store. Then, get a tasty drink that is between 3% and 9% alcohol. Good options are (not too light) beer or diluted wine; one can also just mix grain alcohol or vodka into any liquid to get it to the right alcohol percentage. Then, just mix 1 part vinegar with 4 parts tasty alcoholic beverage in a jar, cover the top using a paper towel attached with a rubber band, and wait! 

This is really it - over the next 4-8 weeks, it will become substantially more acidic and the flavor will change, almost always for the (much) better. You will probably also have a small cellulose mat develop on the top that looks something like a Kombucha SCOBY. It is often referred to as a vinegar "mother," but I usually just call it a SCOBY. This is occasionally not present, but is a good sign. Taste frequently, and when you feel it's ready, throw it in a bottle and use as you desire!

(Note: As with all fermentation, what you get out is limited by the ingredients that you put in. Better alcohol = better vinegar.)

What's going on here?

Acetic Acid Bacteria (AAB) basically eat alcohol and produce acetic acid (vinegar). Over time, these bacteria will turn your alcoholic beverage into a vinegar-y one. The reason that we cover using a paper towel and not a regular lid is that AAB are obligate aerobes, meaning they require oxygen to function. If you don't let your ferment have access to oxygen, it won't turn to vinegar!

Advanced Techniques & Troubleshooting

Aeration (is it worth it?):

Conclusion: Aeration is probably not worth it, unless you're in a big rush or dealing with fresh juices where time is paramount.

Details: Aeration refers to the general process of attempting to introduce air into your vinegar to speed up the brewing process. I first came across this in the Noma Guide to Fermentation, but my understanding is that this process has been around in various forms for a long time.

The idea here is that, since acetic acid bacteria require oxygen to function, they'll work faster if you introduce oxygen directly into the liquid medium. It doesn't seem to be very controversial whether or not this works, although I have wondered how much of the speedup comes from the extra oxygen and how much of it comes just from agitation of the liquid.

The way that the Noma Guide recommends doing this is to buy an aquarium air pump and air stone (~$20 at a pet store or on amazon), and just basically run bubbles through your vinegar liquid. They advertise this mostly for vinegars that you're making directly from fresh juice, where speed (and thus freshness) are at a premium. This can bring the process down from 4-8 weeks to 2-3.

This made me wonder: why doesn't everyone aerate all their vinegars? Is there some downside, or is it just the same vinegar in half the time? 

I've done a number of experiments now, and have come to the conclusion that aerating vinegars, while speedier, is usually annoying in practice.

Basically, in order to run a tube into your vinegar, you have to do so through the side of your paper towel. There are a few problems with this. The first is that some effect (which I have yet to definitely identify) usually causes the paper towel to get wet. I'm not sure if the bubbles cause some sort of splashing onto the towel, or if the liquid is somehow traveling up the side of the tube, or if there's something else going on. However, the towel usually gets wet, and attracts *tons* of fruit flies. Furthermore, the tube going in the side of the paper towel sometimes creates a miniscule gap that will allow a fly or two to get into your vinegar, which is probably gross to most people.

Second, the aeration causes the vinegar SCOBY to glom onto the outside of the air stone. This means that every once in a while you have to clean the air stone or bubbles will basically stop coming out. Either way, at the end you'll be left with a mass of cellulose attached to the outside of your stone, which can be surprisingly tricky to clean.

Third, running an air stone through your vinegar liquid will cause some things to foam intensely, including with some of the juices suggested by Noma. Many beers, in particular, will produce essentially infinite foam when subjected to this treatment. This effect seems to decrease with time, but there are certain beers that seem to foam essentially no matter what. I once got beer all over my basement from overflowing foam (not what you want).

To me, one of the appeals of vinegar is that it's really easy and you can just leave alone until its done. Aeration (at least in the way that I have done it) seems to make it require maintenance. As a result, unless time is really important to you (for freshness, as in Noma, or because you're impatient) then I don't recommend aerating your vinegars.

Alcohol Percentages (does it need to be 3-9%?):

Conclusion: 3-9% seems to be a very safe starting percentage. Depending on the alcohol being fermented, some things seem to be OK also at 10-11%; this may depend on other factors such as higher starting acidity or salinity. Higher alcohol percentages (i.e. undiluted wine) has mixed results.

Details: Most sources you will read on the subject of vinegar-making claim that you need to start with a liquid that is between 3% and 9% alcohol. However, most people have had the experience of an old bottle of wine turning "sour" and smelling vinegar-y, and most wines are in the 11-14% range. Additionally, from a flavor perspective, I don't like the idea of diluting wine if I don't have to. So, I decided to test the limits of this, and test the same wine at 3 different levels of dilution.

The experiment worked as follows: I used the same volume of liquid in 3 different jars. Jar 1 contained wine diluted to 8%, jar 2 contained wine diluted to 10.5%, and jar 3 contained undiluted 13% wine. Each jar also had about 20% of the total volume in starter vinegar.

Jars 1 and 2 worked as you would expect. The vinegar was very nice from both, but jar 2 was stronger in both flavor and acidity. Jar 3 was mixed. It did eventually develop a SCOBY, but much more slowly, and never really turned into vinegar in the way I would have wanted. I would probably not try to make vinegar this way.

On the other hand, I have tried to make vinegar out of a 10% alcohol sour beer. Interestingly, this behaved more similarly to the undiluted wine; it did eventually develop a SCOBY, but the process was slow and noticeably less smooth than with lower-alcohol beverages. My guess is because this was a sour beer and had extra acidity present at the beginning that further inhibited microbial growth, but I can't be sure.

Bottom line, it seems that often one can make perfectly nice vinegar with a starting alcohol percentage of 10-11%, but exact mileage may vary. Exactly how you should do this will depend, likely, on your intended use. The vinegar made with 10.5% wine was delicious but very intense, and would need an eventual use that could handle that kind of flavor and acidity. If you're happier with a more mild-tasting vinegar, then it certainly easier to work with lower alcohol percentages

One final note: I have occasionally been lazy and just poured a bottle of wine undiluted into an already-fermenting jar of vinegar. This has always worked out fine; however, in these circumstances there was always already a fair amount of vinegar in the jar, so perhaps the alcohol was just sufficiently diluted that it wasn't a problem. I would eventually be interested in experimenting with this phenomenon.