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
First Timer Apple wine 36The primary foamed and bubbled for about a week, then slowed down. I didn't have time to transfer it, so I added 1cup of sugar. Last night, 8 days...
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 malic citric
nice smells 39Pinky is exactly right. Many people expect fruit wine to taste like the original fruit...
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).
Understanding Wine Technology David BirdYou know, Joe, I have to disagree on Yair Margalit's "Winery Technology & Operations" (I'm leafing through it now). I'm really less enthuiastic about this book... although obviously you've found it of great...
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 buttume 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 breastration works, you buttume that all the acid is tartaric (or sulfuric).
