For four stages we've fought against it together: acetic spoilage. Work cleanly, keep the air away, top up the airlock so that no oxygen and no wild bacteria tip our mash. In this fifth and final stage I turn the tables. We invite in exactly the microbes I otherwise keep out of the cellar with discipline, and make a craft of it.
In 1998 acetic spoilage cost me a 20-litre demijohn of apple wine. I hadn't topped the demijohn up fully in the neck, air stood above, and it was a warm late summer. After three weeks half the room smelled of salad dressing. Back then that was a loss. Today I know: that was no accident, that was biology doing its job. I had only accidentally held the door open for it. Precisely this door we now open deliberately.
Acetic spoilage, from enemy to craft
Wine fermentation is anaerobic: yeast eats sugar with air excluded and makes alcohol. Vinegar fermentation is the exact opposite. Acetic acid bacteria of the genus Acetobacter need two things I avoid like the plague in the wine cellar: alcohol and oxygen. From both they make acetic acid and water. That's why acetic spoilage in the wine barrel is a catastrophe and in the vinegar pot the whole point of the exercise.
Don't confuse the vinegar mother with the kahm film that grows on badly kept wine. The kahm film is a thin, wrinkled yeast layer and a fault. The vinegar mother is a glassy, gelatinous cellulose biofilm in which the bacteria sit. It sinks, floats or grows as a thick disc at the surface. It feels like a moist jellyfish and is exactly what you want.
Two mothers, two characters
There isn't the one vinegar mother. A culture adapts to what you feed it. An apple vinegar mother is used to mild, fruity apple wine and delivers a soft, light vinegar. A red-wine vinegar mother copes with the tannins in red wine, which first slow down an untrained culture. The result is a dark, hearty wine vinegar.
You can, in theory, retrain a mother, but that costs weeks and sometimes goes wrong. I'd rather take the fitting starter culture straight away for what I intend. Whoever starts small should stick with apple, that's the more forgiving path.
The set-up, step by step
The most important point first: no metal. Acetic acid attacks metal and the culture doesn't like it. I work with a wide jar, a stoneware pot or food-grade plastic. Wide is more important than tall, because the bacteria work at the boundary with the air. Lots of surface means faster vinegar.
- Dilute the wine. Acetobacter works most happily at about 5 to 6 % vol alcohol. Finished wine at 12 % is too strong for it and slows it down. So I blend roughly 1 part wine with 1 part boiled, re-cooled water. The exact dilution is in the instructions for your vinegar mother, and I stick to that.
- No sulphur. Take a wine without or with very little sulphur. Sulphur is there to kill exactly these bacteria. Heavily sulphured supermarket wines are a slow start.
- Set it up. Diluted wine into the vessel, vinegar mother together with its liquid added. Fill at most two thirds, the rest is air space that the culture needs.
- Cover, don't seal. A piece of linen or a coffee filter, fixed with a rubber band. Air must get in, flies must stay out. A tight lid suffocates the fermentation.
- Stand it warm. 20 to 30 °C are ideal, most happily around 28 °C. Below about 18 °C the culture turns sluggish and you wait forever. Dark and draught-free, but not in the cool.
Vinegar flies and the weeks of patience
Vinegar attracts fruit flies like nothing else. That's no cosmetic problem: the creatures carry wild acetic and other bacteria around with them and drag foreign germs into your batch. A cleanly stretched cloth without a gap at the edge is mandatory. Check the edges, that's where the little ones otherwise slip through.
And then it's a matter of waiting. Depending on temperature and culture it takes four to eight weeks, sometimes longer, until the alcohol has soured through. Smell it once a week. At first it smells winey, then pungently alcoholic, at the end clearly of vinegar. You don't have to stir, the mother regulates that at the surface. If you're in a hurry, you're in the wrong place here. Vinegar, like wine, is a school of patience.
The strict separation, or you lose both
This is the paragraph you should write behind your ears. Vinegar and wine must never stand in the same room. An open vinegar vessel is a bacteria catapult. The Acetobacter spread through the air and via every fruit fly that flies from the vinegar to the wine demijohn. If you draw your vinegar next to the fermentation cellar, sooner or later exactly the acetic spoilage we fought against for four stages will hit your wine.
I therefore make my vinegar consistently elsewhere: another floor, another kitchen, the garage in summer if need be. Own funnels, own tubing, own cloths that never come near the wine cellar. Wash your hands before you switch from the vinegar to the wine. That sounds strict, and it is. I paid the price for carelessness in 1998.
Harvesting and tending the mother over years
When it tastes cleanly of vinegar and no more alcohol comes through, you carefully draw off the finished vinegar. Important: leave the mother and a good bit of liquid in the vessel. That's your living starter for the next round. Simply add freshly diluted wine, and the game begins again. A well-tended mother accompanies you over years, it grows thicker and stronger with every feeding.
The freshly drawn vinegar is sharp and unrefined. Fill it into a bottle and let it mature cool and dark for two to three months, then it rounds off and turns soft. Whoever wants to stop the souring and store the vinegar long-term heats it briefly to about 60 to 70 °C (pasteurising) and filters off the cloudy matter. I mostly leave mine naturally cloudy, that's a matter of taste.
With newcomers I like to start with the apple vinegar mother, because a mild apple batch forgives if the temperature fluctuates now and then. For strong, dark wine vinegar from red-wine leftovers I take the red-wine vinegar mother, because a culture already used to red wine and its tannins gets straight to work instead of laboriously retraining itself first. Both are living cultures, not powders, so grant them a day or two of rest at room temperature after delivery before you set them up.
With that the circle closes that we began four stages ago. From the first demijohn of must to your own vinegar from the leftovers. Nothing is poured away, everything comes back. That's how the people before us did it, long before there were cultured yeasts and check digits. It's worth carrying this knowledge onward.
From the cellar, Magnus