[vmelkon]

Does anyone know why vinegar is 4 to 6 % acetic acid?
Why do they sell it in 4 L jugs and waste money on transportation when they can sell a small quantity of pure acetic acid and the home cook adds the water himself?

I was thinking that maybe their manufacturing technique results in low concentration acetic acid.

Also, will it concentrate if I leave it out or is acetic acid volatile?

[Arkcon]

Ha Ha Ha.  Brilliant.

OK.  Yes, the fermentation of sugars to wine by yeast generally stops at around 10% ethanol, and the bacterial oxidation of the ethanol to acetic acid produces, at most 6% acid.  Even the distilled white vinegar is re-diluted to 6%.  We're all used to that household strength, it makes good salad dressing and adequate pickles.  The acetic acid in vinegar is generally believed to be produced by this "natural" process, and not industrially.  'Tho its hard to believe that actually matters for the white vinegar.

And no, glacial acetic acid is too hazardous for household use.  The solvent will go straight through a person's skin, causing severe damage, after in gets underneath, mixes with water, and becomes a very concentrated acid solution.

This is what's so funny.  When I was 7 or 8, I tried to concentrate vinegar by evaporating it, to create the super acids.  I tried to dry vinegar, scrape it into emptied medicine capsules, and convinced myself I'd created super acid to destroy things with.  Other kids believed me too.  Alas, no, the active ingredient is too volatile for concentration by evaporation, you will need to distill.

[Borek]

70% acetic acid is sold in some European countries - like Austria. See an old thread here: http://www.chemicalforums.com/index.php?threadid=7014 - unfortunately, attachment disappeared. But it was there.

[Arkcon]

Well, that's pretty exciting.  I guess if you want real strong pickles, or have some corroded metal to "pickle."  I guess its aqueous enough that its no longer as permeable to skin.  'Tho I wouldn't want to be the one who tests that.

[Borek]

From what I remember Alberto told us it is used just as you would use tabasco sauce - a drop or two to make something more spicy.

Ah, it was called essig essenz!

[vmelkon]

And no, glacial acetic acid is too hazardous for household use.  The solvent will go straight through a person's skin, causing severe damage, after in gets underneath, mixes with water, and becomes a very concentrated acid solution.

I'm sure you can wash it off and continue cooking. It is not as if you are dealing with hydrofluoric acid.

[CrimpJiggler]

I agree, it would be way more practical if the vinegar was more concentrated. Have to look at it from the manufacturers point of view though: sooner or later, an irresponsible consumer would injure themselves with concentrated acetic acid. Then again, they could injure themselves will dilute vinegar too but you can't really hold the manufacturer responsible for a consumers stupidity.

I attempted to concentrate vinegar once by partially freezing then filtering out the frozen acetic acid and discarding the liquid water. From what I remember, something unexpected happened, rather than the ice being the acetic acid, it was the liquid that turned out to be more concentrated.

[fledarmus]

Glacial acetic acid is too irritating to the nose and throat to be used regularly in the typical unvented kitchen. Even vinegar can be an issue when you are boiling it, and it is much less concentrated!

For CrimpJiggler, the "unexpected" result of the ice freezing out of a vinegar solution can be explained if you look at a phase diagram for a mixture of acetic acid and water (shown below, from http://www.chem.queensu.ca/people/faculty/mombourquette/firstyrchem/liquid_soln/index.htm

[CrimpJiggler]

For CrimpJiggler, the "unexpected" result of the ice freezing out of a vinegar solution can be explained if you look at a phase diagram for a mixture of acetic acid and water (shown below, from http://www.chem.queensu.ca/people/faculty/mombourquette/firstyrchem/liquid_soln/index.htm

Thanks for clearing that up. Thanks for the diagram, first time I've seen a phase diagram for a mixture. I'm guessing that room temperature is at the top of the axis. If I'm not mistaken, plain white vinegar is around 20% acetic acid so the starting mole fraction should be well to the left of the x axis. Yep, that explains it. So after 1 or 2 filtrations (to get rid of the frozen water), the mole mole fraction should be high enough that its the acetic acid that starts freezing. Now that I know this, I could devise a far more effective method of concentrating AcOH.