I often end up with wines that have pH's that are either too high or too low, and the best solution is to blend the two. My question is how to predict the resultant pH.
Obviously, pH is a log function, so blending equal parts of wines with pH's of 3 and 4 DOESN'T produce a wine with a pH of 3.5. A wine with a pH of 3 has 10 times the concentration of H+ ions than a pH of 4. Does anyone know of an equation to predict a resultant pH of a blended wine the following 4 variables:
X = volume of wine with pH of A Y = volume of wine with pH of B
My goal is to work backwards and aim for a specific pH, knowing the pH's of the original components and then calculating the necessary volumes of the two components. While bench trials are another solution, there should be some science to predict the results.
I'm an unemployed chemist, so conceptually, this is an easy topic for me. But ...
1) You use conc of the acid and base, not the pH to determine how much of each
2) You need the value for pKa, which is a constant. Now, that number is published for citric, malic, and tartric acids, but what about the other acids, and how much of each. You can't know this without an expensive lab test.
3) Here's my question: Do you really need to get an exact final pH to make the wine the proper flavor and stability?
I figure, you're just going to have to use trial and error to get to where you want.
That is fine and all, but you also have the problem with different buffer systems (the Henderson-Hasselbach equation is for determining pH in a buffer system, if the acid/base does not buffer but instead completely disociates in water like HCl then [H] = [HCl] and pH = -log [HCl] - for the non chemists). So you have multiple pKas to deal with. You have bicarbonate buffers, phosphate buffers and several organic acid buffers (tartaric, malic, acetic, succinic, citric and more).
You could make the assumption that the dominate acid will determine the final pH, in in use you will find that assumpion does not work that well.
Mathematically the answer is yes. You can use the Pearson's Square -- but not exactly as it is normally used. As you comment, the pH scales are log based. So first you need to take the exponent of each pH. Then use the Pearson's Square. Then take the log of the final number.
There are "got'chus" however. pH is not going to blend like alcohol. As commented above, the different buffer systems and different acids that will interact differently when the wines blend will change the pH. You might blend them and check the pH and find it is quite far off from the predicted value. In fact you might blend them and check the pH and then check it again a week later and find that it has changed considerably from the first measure.
It might work but I am not sure it is valid to talk about blending pH.
With all deference to the scientists who have already replied, why not use a simple bench trial to determine the desired belnd proportions? Take a known quantity of Wine 1, measure the pH. Add a known quantity of Wine 2, blend, and test pH. Increment until you get to the desired level.
I use a Pearson square to give a rough indication, then start from a more conservative assumption, adding incremental amounts of Wine 2 until reaching the desired blend acidity.
"Huh?" Might you chemists pls dumb down the discussion for us scientifically impaired readers? Simple english preferred.... among the challenged, bobdrob.
Interestingly, the only one of Jack Keller's conversion calculators that DOESN"T work (i.e., when you enter the numbers and click "submit", nothing happens) is the one for predicting pH. Maybe Jack (whose advice I take as gospel) knows that this isn't a simple conversion.
Yeah, I just found that link on Google when I searched the question, so I just posted it blindly. ;) The values for pH should be on a log scale, and they are affected by relative amounts of the various acids in wine. I completely missed the concept of buffers in wine, maybe they're there, maybe not, I don't know for sure. Then there's the alcohol, that removes some of the acid's activity, and shifts the whole mix closer to neutral. They why when you test a finished wine with a pH meter, you should heat lightly to boil off some alcohol.
Bah. If the two wines are similar in type, and likely have the same levels of various acids, mixing them might produce the correct pH. The logs cancel out, don't they? If I'm wrong, just call it a brain fart and move on ...
No one's answered my question. Does anyone really need to get the pH value of their wine that tight? Most websites recipies and winemaking books suggest just adding some acid mix or potassium carbonate to move the pH down or up, respectively, or mixing over acid and over alkaline wines, as the flavor of the wine requires it. Does anyone really get their pH to exactly 3.5 or whatever?
I made a batch of Welches wine last March. I put a little too much lemon juice and rind in, and it was very tart when bottled in June -- perhaps only good as a marinade. I tasted some today, its mellowed a lot -- just like conventional wisdom said it would. So I figure I was right to not sweat the pH with this wine.
Probably. It will be unless the blending brings about a chemical reaction or changes the buffering capabilities which could cause it to be outside the original range. That said, I would expect it to be between. But I would not blend a lot of wine without benchmarking it.
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
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malic
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citric
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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).
To answer yuor question, no. (In my opinion.) I use pH to decide how much sulfite I need and to get a ball park on acid balance; it only takes a few more minutes to get TA. too.
I use TA as a baseline when adjusting wine acids, it's just easier for me to understand. High pH usually equates to low TA, and both usually equate to a dull, bland wine. High pH and high TA usually mean you have excess potassium but if you want to get it down you still add tartaric and chill. It means watch that wine closer, I had a Pinot start at 3.6, creep up to >3.7 after fermenting and a month later it was at >4.0 and just awful. I used phosphoric on that one although you can't use that commercially. (If it's legal for soft drinks I do not understand why it's not for wine, but no one pays for mine so there...) I still did not like that wine, it was 'thin'. I won't use phosphoric now, just tartaric unless I have a good reason to use malic or citric.
I would prefer to bottle wines at a pH of 3.6 or lower but have bottled at 3.85 and drank those up to 3 years later with SO2 at 50- 60 PPM with no problems. If I was in a commercial operation that fed my family I would not do that though; the giudelines that report issues with wines over pH of 3.6 were made by other failures so luck of the draw is no excuse to ignore them..
Taste is the best tool you have, the most important thing I have learned over the years is my instincts are now better than my instruments, if they disagree my instinct wins and I adjust based on that. I can always remeasure and adjust again. I could not say that 5 years ago, I just needed more time with evolving wines (and keeping track of what I did to see if it was the right call) to develop that.
It's like having a good 24 ounce framing hammer and a finish nailing hammer, if you want to play with wood you should have both because each does its job particular better than the other and sooner or later you will need both.
An excellent description of what is going on and an excellent explanation of why people who try to apply too much science to the art of winemaking are destined to frustration!
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