Questions about Vinegar

[JT101]

Making a batch of vinegar from my pressed apple juice this year. Wasn't doing anything at first, but then once I put it somewhere warmer, I saw a fruit fly in there, and then it started to build up a film on top, so we'll see how it goes. The 2-4 weeks a lot of people state seems a bit optimistic. It's been in there 3 weeks already. Anyway, patience......I'll report back with my findings.

The main questions I've got are more curious than anything else.

1) So I understand that vinegar can either be made from the sugar base liquid such as malted barley mash or fruit juice, OR it can be made from an alcoholic liquid. For example, everyone seems to make ACV from apple juice, whereas Wine vinegar is made from red wine, rather than grape juice. Why is this so? Why is ACV not generally made from cider, and wine vinegar from grape juice. Surely the end result must be the same if both yeast and bacteria are present.

2) Second question relates to acidity. A typical cider ends up around 6%, so based on what I've read of an approximate conversion of ethanol to acetic acid 1:1.2, you'll end up with around 6-7% acid vinegar, so nothing really needs to be done to it. But with red wine, even if you use a low end 10% ABV wine, you'll end up with say 11-12% acid vinegar. A bit overkill for preserving. So the question is, should you dilute the wine first, or dilute the vinegar afterwards? And what would be the pros and cons.

Thanks

[Green Aura]

I don't think I can answer your questions but I've made vinegar in two ways.
1) a gallon of herb wine which was disgusting to drink - left in DJ on sunny windowsill with loosish plug of cotton wool for a couple of years. It may well not have needed that length of time but we forgot it, hidden behind the curtain. I've no idea of the acidity (I've no way of testing) but it's delicious, especially as part of a salad dressing.
2) Apple scraps (mainly cores as I rarely peel apples) collected in jar, covered with water. If memory serves I added a bit of raw ACV to speed up the process and it was pleasantly vinegary in about a month or so.
I don't use vinegar for preserving, except for the odd jar of chutney (and even then I'm more interested in lacto-fermented chutneys these days). However, again from memory, we made chutneys to sell in the bakery and the food regs required a minimum 5% acid.

[JT101]

I'm definitely struggling with my vinegar. I've 2 containers. One is full of cider and one apple juice. The apple juice had a think film of bacteria on top but once i stirred it that disappeared. The cider container stiĺl looks and tastes like cider. No film on top. The apple juice definitely had a few fruit flies land in it. I moved both wide knecked containers to my airing cupboard where it is 24C. I also added some of that Braģgs ACV and yet still nothing is happening. Been over 5 weeks now. Any ideas anyone?

[BernardSmith]

A couple of thoughts. To make vinegar you need to start with alcohol. In other words, acetobacter in the presence of air can turn wine (or cider or beer) into vinegar, but they cannot turn fruit juice into vinegar without that juice first fermenting. Now, if the juice has been made with any preservatives (sorbates, for example) yeast will not be able to ferment it.
In other words, apple cider vinegar is made from hard cider (I am in the USA and cider here is used to refer to the soft drink), not from "apple juice" ... unless, of course, the juice has been allowed to ferment first so it will be cider and not juice.