If you are interested in the subject of making your own vinegar, and you want to learn more about vinegar-making than you will get from the average online tutorial, you will appreciate this 28-page PDF download (with 10 illustrations). It will give you some historical perspective along with the practical information. Here is how the bulletin describes itself...
"Vinegar can be made from any fruit, or, in fact, from any material which contains enough sugar and is in no way objectionable.
Whether it is done on a small scale in the home, or on a larger scale on the farm, or in a still larger scale in the factory, the production of vinegar is the result of two distinct fermentation processes—an alcoholic fermentation followed by an acetic fermentation.
By using the materials and following the methods discussed in this bulletin, vinegar of good quality may readily be made from apples, peaches, grapes, and other fruits, large quantities of which are wasted each year in the United States."
The making of vinegar using apples, grapes, oranges, peaches, persimmons, pears, berries, honey, maple syrup, watermelons, grains, and molasses is discussed. Fermenting, filtering, clarifying, aging, pasteurizing, and packing are also covered. In addition to simple home vinegar production, a larger-scale, continuous-barrel process is explained. For commercial vinegar production, the bulletin describes how to make and use a "quick vinegar generator."
There is also a discussion of "Causes of Failure" and "Animal Parasites" (vinegar eels and vinegar mites).
Testing for acid strength of the vinegar is covered near the end of the bulletin. However, the testing process in 1924 seems better suited to someone with a scientific or laboratory background. The bulletin ends with "Federal Regulations Governing The Manufacture And Sale Of Vinegar."
P.S. For an online tutorial on the subject of making your own apple cider vinegar, check out this link: How I Make Apple Cider Vinegar