Rescuing A Stuck Vinegar Barrel
If you make your own wine vinegar, you've probably smelled it: You may describe it as nail polish remover, vinyl, or airplane glue. But you know it doesn't smell like vinegar.
Most of the time, your vinegar may smell like that for a while and then find its way to a more classic vinegar aroma. But in the back of my mind, I have always remembered Ed Behr's commentary in his article "The Best Red-Wine Vinegar You're Likely to Find is the One You Make Yourself": "… some batches I throw out. Those have a strong, unpleasant aroma of nail-polish remover."
And it finally happened to mine. It had smelled like nail polish for too long.
I mentioned it to the staff at Oak Barrel Winecraft. Their response echoed Ed's. "Just toss it out and start over." I sadly mentioned this on Twitter, but Judy Witts Francini stayed my hand and suggested that I look at a book called Lost Arts. By coincidence, I had it on my shelf.
"Occasionally vinegar may develop some 'off' odors, the most common being that of ethyl acetate, the familiar smell of nail polish remover," writes Lynn Alley, the author. "Before you throw your vinegar out, try aerating it." She suggests pouring it back and forth between jugs, but I was able to use a whisk to whip the liquid into a frenzy. Then, just to be safe, I added a fresh batch of starter culture, "mother," into the barrel. I also added in some more wine to give the culture something to eat.
The nail polish smell persisted, but the overall aroma had improved. A few weeks later, I sniffed again and cried out in triumph: My barrel once again smelled like vinegar. I bottled the bulk of it and replenished the barrel with fresh wine.
But how could I avoid this in the future?
There's no way to get rid of ethyl acetate completely. In fact, it's desirable in small amounts. Ethyl acetate is the dominant ester in wine and contributes to its fruit aromas and, by extension, those of the vinegar you make from it. And a vinegar barrel with a between-wine-and-vinegar liquid is the perfect environment for creating it: Ethanol and acetic acid can react to make ethyl acetate. I accepted its inevitability, but I wanted to know how to contain it.
I spent an afternoon poring through journal papers about vinegar, but most of them dealt with industrial vinegar production, which shares only a basic biological fact — Acetobacter converts ethanol to acetic acid in the presence of oxygen — with my little barrel. (In submerged acetification, the preferred industrial technique, oxygen gets sucked into the liquid and shattered into small bubbles by a rotor. This creates a huge air-and-liquid interface, which lets the culture convert a batch of wine into vinegar in a short period of time.)
I turned from the library to Katz and Co., one of the few producers in the United States that makes vinegar via the Orléans method, which is much closer to the home vinegar maker's setup. Albert Katz was understandably reluctant to share the details of research he has done to reliably produce high-quality vinegar for his business, but he did offer some pointers: "The most important thing about making Orléans method vinegar is to make sure you are doing everything right," he says. "By that I mean using the appropriate alcohol with proper acidity levels. The contents must not be too high in SO2, or you will inhibit conversion and the temperatures must stay correct." He added that both the environment and the equipment must be as clean as possible
I looked at his email and then at my little barrel. It sits on the mantel in our living room, where temperature varies often. It receives random glasses and bottles of wine from dinner or from tastings. I doubted that's what Katz meant by a well-controlled setup.
But his advice and my research gave me ideas about how to keep my vinegar happy, and they are the hypotheses I'm working from now.
Aeration is key, as Lost Arts mentions, to a healthy Acetobacter population. In a 2008 review article by Eveline Bartowsky and Paul Henschke about wine spoilage, the authors write, "More recent studies have shown that momentary aeration, such as that introduced by agitation or racking of wine from one barrel into another is sufficient to encourage significant growth of resident AAB [acetic acid bacteria] populations." Now, I whisk my vinegar every few days through the large hatch Melissa made for me on the side of the barrel. If you have the traditional kind with a small bunghole, you can probably aerate it by draining some amount of the liquid into a measuring cup and then pouring it back in through the top. I've thought about adding a pump from a fish tank.
As I thought about Katz's advice to maintain a tight environment, I realized I had become more cavalier about my barrel in the "nail polish" months. In the past I had watered down wine to keep it around 10 percent, which is near the upper end of what Acetobacter can tolerate. But I had begun to just dump leftover wine into the liquid. This probably wasn't a problem in terms of alcohol content — the barrel's liquid gets lower alcohol as it evaporates and gets converted to acetic acid — but I did wonder if I had removed a crucial ingredient: water.
The Fisher-Speier esterification pathway describes a reaction in which ethanol and acetic acid exist in equilibrium with ethyl acetate and water. Remove water from the barrel, and the equilibrium will move to the ethyl acetate side of the fence. Add water, and you shift equilibrium back to the ethanol and acetic acid side. By watering down the wine to 10 percent, I was not only keeping the alcohol levels in check, I was keeping the equilibrum tilted in my favor.
At least, so goes the theory. Testing it is a bit awkward: The results are either "it stuck, so that didn't work" or "well, it's gone long enough without getting stuck that that probably worked." But my current vinegar batch still has that complex aroma of nail polish remover and vinegar that I have for a long time associated with an in-transition batch.
So far, so good.