Unlike many home brewers and winemakers, I make vinegar intentionally. Its a slow process that results in a probiotic with flavor options not available commercially.
I use a two step fermentation process. The first step is to make alcohol. Good vinegar results from first making a good alcoholic beverage. I measure the specific gravity of a fruit juice with a hydrometer. This reveals the sugar content and potential alcohol level of the beverage. Higher sugar content will ultimately lead to a higher acidity in vinegar. I add yeast to the fruit juice or malt to get the alcoholic fermentation started. The container is a jug or carboy to which I attach an airlock.
After three weeks the airlock is usually no longer bubbling which shows that the fermentation has slowed. I check the specific gravity. With some basic math I can determine the alcohol content. I also smell and taste the beverage. It is then ready for the second fermentation.
Depending on one’s perspective, I either ruin or redeem the beverage. I add raw vinegar which contains active bacteria that transforms alcohol into vinegar. The vinegar bacteria needs air so this fermentation proceeds faster in a crock than in a narrow neck bottle or carboy. The container needs to be covered with a cloth to keep out flies but allow air exchange. In a crock, the vinegar fermentation can be complete in less than a month at room temperature.
I currently have a pear vinegar in a gallon jug that is taking its time on its way to vinegar. I added raw vinegar in October and now in early February it still has a sweet/sour taste. Its a wine vinegar that’s still part wine. Friends and family have enjoyed shots of it. Its also great for deglazing a pan. Slow home food and beverages are the best.