It's impossible to say for sure what elements you're tasting, but it isn't vinegar. We don't use vinegar, or anything like it, in any of our flavors. I know it's suddenly become trendy to add all sorts of things to swing the ph of e-liquid, but I don't believe in it.
What you're likely to be tasting is merely fresh liquid. We make our liquids only after you order, and many of our flavorants (including several that make up Robacco Caramel) are alcohol based extracts. They need some time to blend to taste. This will differ for each person, as some prefer them almost right away, some prefer to let them age weeks or months. Given that there are as many opinions on the subject as there are people, we opt to go for fresh so that you have full control over how long your liquid steeps. The first whiff off the bottle may show some of the alcohol character, but it fades pretty quick in any liquid.
I'm also concerned that you may be characterizing the nicotine flavor as "vinegar", as you did order 32mg/ml... and you appear to be a new user, if your join date on ECF is any indication.
Good, fresh nicotine, in it's most pure form, has a single sharp note to it which most closely resembles black pepper. This will meld and fade with many other flavors, and in fact works well in blending with most tobaccos, but will sometimes still stands out in other flavors, and to users who aren't used to such a high concentration.
We blend down all of our own liquid bases, starting with 99%+ pure nicotine. From the day that arrives to us, to the day we empty the bottle, it's crystal clear and with no skunky flavors. We store it in airtight vessels at subzero temperature to slow it's oxidation to a crawl. Again, this allows us to ensure that the only thing you taste in the nicotine base, is the nicotine, with a single, sharp, true note.
If you're used to more heavily oxidized liquids, like you'd find in pre-filled cartridges, you may not have experienced that before, especially in such a high concentration.
ETA: Thank you, oldsoldier, for giving me an opportunity to respond to this thread.