WHY THIS RECIPE WORKS: The process of making vinegar seems to be shrouded in mystery. There’s talk of mothers, bacteria, feeding schedules, oak barrels, botched batches, sterilization, and the smell of acetone. You’ll find online rants debating the value of a watered-down wine stock or whether you should add quantities of wine as a vinegar ages.
All of that intimidating lingo obscures the fact that, really, vinegar is just wine that’s been encouraged to go bad. Sure, there are plenty of variables, but do you really need anything more than a little wine and some patience? We found the answer is no. The one key is using a mother. In theory, you could let wine turn to vinegar on its own, but the timeline is long and the results inconsistent. It’s far better to start with a “vinegar mother,” a culture that helps acidify the wine, whether it’s store-bought or gifted from an industrious vinegar-making friend. Throw in some wine and water, and you’re in business. We prefer vinegars made with full-bodied wines like Syrahs or Chardonnays, but honestly, just use a wine you like since the vinegar will echo its flavor. Vinegars made with organic, low-sulfite wines fermented slightly faster for us, but the difference was mostly negligible over a few months.
Many D.I.Y. wine vinegar recipes call for complicated steps like feeding (with additional wine) or aerating, but we found the simplest method gave us the best vinegar and was the most reliable. After mixing the wine, water, and culture together, all you need to do is wait. Note that white wines take about a month longer than reds since they usually have more sulfites in them that need to dissipate before the fermentation process can begin.
—Addy Parker, Associate Editor, and Kate Williams, Test Cook, Books
It starts with a mother: Wine could turn to vinegar on its own, but we jump-start the process by adding a "vinegar mother" culture, which is basically a blob of starch filled with the acetic acid bacteria needed to acidify the wine. There's a near-direct correlation between the percentage alcohol you start with and the vinegar's final acid concentration, so we dilute the wine with water using a 2:1 ratio. That will give you a vinegar with around 5 to 7 percent acidity. We use an opaque ceramic gallon-size sterilized crock, but a glass container wrapped in a towel to keep out bacteria-killing light also works.
Let it breathe: The bacteria need oxygen to flourish, so don't completely seal off the crock. Instead, cover it with a clean kitchen towel, which will keep fruit flies out, then place it in a relatively warm space. The ideal temperature for fermenting vinegar is around 75 to 80 degrees; cabinets above the fridge, stove, or oven work best. Temperatures slightly below or above this target range will work, but the fermentation time will vary slightly.
Beginning to grow: After 10 days, the mother should be starting to form. Usually it looks like an oil slick, but if it's very active bacteria, you may see larger pieces. The mother will be opaque and slightly lighter in color than the wine. If you're working with white wine, you may not see much until almost a month has gone by. White wine generally has more sulfites than red, and therefore can take longer to turn to vinegar. It could take a week longer than these estimates to see something, but if the slick never appears, there's likely something wrong with the mother and you should start over with a new one.
Turning wine into vinegar: After three months, the mother should have grown substantially. The vinegar should be ready by this point, although the only way to know if it's ready is to taste it. Depending on how much your crock has been moved around during fermentation, and depending on when you harvest your vinegar, you may see tiny pieces of mother floating on the surface instead of a flat sheet. Don't worry; that's normal and safe. You'll also notice there's been some evaporation, which will vary depending on several factors, like room temperature and your crock's dimensions.
Mother removal: It's time to remove the mother from the crock. You can simply pull it out with your hands (wear gloves if you're squeamish). There will still be some bits floating in the crock, but we'll take care of those momentarily.
Saving up for the next batch: Rather than throw it out, we always save our mother for making future batches (or to give away to fellow vinegar makers); it will keep for three months at room temperature. If you're ready to make more vinegar right away, you can simply break off a piece of mother and start all over. For later use, break off a 2-inch piece from the mother and transfer to a 4-ounce jar with a tight-fitting lid. You'll cover it with some vinegar for storage, but you need to strain the vinegar first. (You can prep more of these if you want to give some away.)
Clean it up: The small floating pieces of mother left in the crock are totally harmless, but they aren't pretty to look at. We like to strain them through a coffee filter±lined fine-mesh strainer to ensure clean, clarified vinegar before bottling. At this point, you should take some of that strained vinegar and pour it over the bit of mother you just put in the jar until it's covered (around 1/2 cup for a 4-ounce jar).
Fill 'em up: Despite the straining, there are still bacteria in the vinegar. To prevent the vinegar from continuing to ferment, you want to fill your bottles all the way to the brim. Since you introduce oxygen (aka food for acetic acid bacteria) each time you open the bottle, and it takes a while to go through a large amount of vinegar, divide the final product between a couple of bottles for storage. This way, you will have just one bottle in use and can keep the other closed and oxygen-free. Chances are, you will still see a little bit of new mother forming in your vinegar after it has been opened. This is normal.
Makes 4 to 5 cups red wine vinegar or 2 to 3 cups white wine vinegar
Start today, enjoy in 3 to 4 months
2 (750-ml) bottles full-bodied red or white wine
3 1/4 cups filtered water
8 ounces red or white wine mother of vinegar
1. Combine wine, water, and mother of vinegar in sterilized 1-gallon ceramic crock. Cover top of crock with clean kitchen towel and secure with rubber band. Place in warm, dark space to ferment, undisturbed, until mixture no longer tastes alcoholic and has a strong vinegar flavor, about 3 months for red wine or 4 months for white wine. After about 10 days for red wine and about 1 month for white wine, mother should be starting to form on surface of mixture (surface will look oily and wine will look cloudy). Oil slick will gradually transform into thick, gelatinous sheet; do not disturb crock during fermentation or mother will break up and become harder to remove.
2. Using your hands, gently transfer mother to separate bowl. Break off 2-inch piece and transfer to 4-ounce jar with tight-fitting lid; discard remaining mother.
3. Line fine-mesh strainer with double layer of coffee filters and set over 8-cup liquid measuring cup; pour vinegar through strainer. Pour enough strained vinegar over mother in jar to cover completely; cover jar and store at room temperature for up to 3 months for next batch of vinegar. Pour remaining vinegar into glass bottles with tight-fitting lids. Vinegar and mother of vinegar can be stored in cool, dark place for at least 6 months.
From The America’s Test Kitchen DIY Cookbook, published by Boston Common Press.