> I completely missed the concept of buffers in wine, maybe
> they're there, maybe not.

A buffer is somethign that resists pH changes. If somethign is
buffered at 7.5 it will take more acid to make it go down than what you
would expect just considering that pH = - log {h} where H is the acid
concentrations.

So what makes bufffers? Any acid that you add that will not COMPLETELY
release its hydrogen atoms into the liquid. For example, you put
hydrochloric acid (HCl) it will split apart totally into H+ and Cl-
ions.

That is not the acid found in wine though. Wine acids are composed of
organic chemicals that do not liketo completely give up their H+ ions.
All organic acids (that we need to be concerned with in wine) have a
carboxyl acidic group. It is composed of a carbon atom (C), two oxygen
atoms (O) and a Hydrogen atom (H). Both oxygen atoms are attached to
the carbon and they hydrogen atom is attached to one of the oxygen
atoms. Like this
O
||
-C-O-H

The "-" in front of the C is where it is attached to the rest of the
molecule (and what makes each molecule different).
Here are a couple links where you can see the "COOH" groups
tartaric
http://www.chm.bris.ac.uk/webproject...erson/e334.htm
malic
http://www.pdrhealth.com/drug_info/n...mal_0292.shtml
citric
http://www.science-projects.com/MolecStruct.htm


It is that difference in the structures that makes each a different
strength acid. First tartaric and malic acid can give off 2 H+ ions,
while citric can give off 3. But more importantly is that when the
acid gives off the H+ it becomes less stable becasue it now has a
negative charge. The rest of the chemical helps stabilize that charge.
So the differences seen in the rest of the chemical affect how stable
it can be without the H+.

Now, since the chemical does not "like" (to keep it non technical) to
lose that H+ all that much, you will find that part of the time, it
finds a H+ floating around and grabs a hold of it, the pH that the
chemical is sitting around with the H attached half the time (and the
other half of the time it is loose) is the pKa...that is a measure of
how strong the acid character of the chemical is. It is also the spor
where the chemical will "buffer" or resist chages in teh pH. If you
add more acid, it gives the chemical more H+ to grab a hold of, if you
take away some of the H+ (by addition of OH-) there are fewer H+ to
grab a hold of. But around the pKa it takes more H+ to make the pH
change than it does if there is a TON of loose H+ floating around (as
if it was a really low pH).


So the different acids that you put in there and their proportions will
affect the ability of the pH to change. Without knowing the exact
concentration of the different acids it is impossible to know for sure
how the pH will act if you mix or mess with it. You can know that it
will go up if you add a higher pH wine or chemical, and you can know
that it will go down if you add a lower pH wine or acid...but you can't
know by how much. Any calculator you will find will have to assume
that the wine had a certain percent of a certain acid (with its pKa) to
guess what it would be with blending. That is how the titration works,
you assume that all the acid is tartaric (or sulfuric).