I don't know - household vinegar, being mostly water, boils at 213F. According to Lina Zeidrich in The Joy of Pickling (1s ed., page 11) "acetic acid evaporates faster than water does. Boil pickling liquid only as long as the recipe calls for." I don't know if she's tested this. I've never seen that statement in any other pickling guide.

In an exhausting (I was up at 3AM and saw your post) search of the Internet this morning I haven't found a definitive answer, but I did find a Wikipedia reference to a Persian alchemist who concentrated acetic acid by distilling vinegar (which would seem to prove Linda's point that the H- volatizes when the vinegar is boiled), and another couple of sites that said they've made concentrated wine vinegar by freezing it then pouring off the stronger vinegar (not pure acetic acid, just stronger vinegar).

I have to get DD off to camp now, will try to search more later today.

Oh, and you have to consider the effect all that boiling is having on your other ingredients too, so it may not matter what happens to the vinegar.

This post was edited by ajsmama on Wed, Aug 6, 14 at 7:36

As the water boils off the pH of the remaining product declines, lowers more into the acidic safety zone.

Dave

I guess the because of the heat that it boils immediately. And also when we boil vinegar we can easily smell it and I think the acidity of the vinegar is boiling and evaporating.

I asked Linda and she is checking into it again, but says that acetic acid will boil off, citric acid doesn't. She said it used to be common advice given on extension sites not to boil vinegar solutions for longer than the recipe specifies because of that.

Tomato-based sauces should get more acidic with boiling down/concentration because of the citric acid in the tomatoes themselves, but I'm not sure of something like a fermented pepper mash (lactic acid), mango-based, etc.