conversion from TA to pH?

[suprasteve]

I ordered a pH tester to retire the strips I had been using (thinking there will be a noticeable increase in accuracy). I've read the range for acid in wine is 2.5-4.5, more specifically 3-3.5 is the 'best' range. I did find this on the forum which helped somewhat:

Here is the PowerPoint slide show that I presented at Winestock this year:
/images/uploads/20071031_043753_pH_Acid_SO2_in_.pps

from Keller's website I've been trying to follow this:
Dry White Grape Wines..........0.65-0.75%

Sweet White Grape Wines.......0.70-0.85%

Dry Red Grape Wines.............0.60-0.70%

Sweet Red Grape Wines..........0.65-0.80%

Sherry Grape Wines.................0.50-0.60%

Non-Grape White Wines..........0.55-0.65%

Non-Grape Red Wines.............0.50-0.60%

Any easy way to convert TA into a pH, like a simple formula, or is it just one of those low TA means high pH things with no clear answer?
Thanks!

 

[Travisty]

I don't believe there's any way to accurately convert a TA number to a pH. Generally, a low TA will correspond to a relatively higher pH and raising the TA will usually lower the pH. However, there's not a direct correlation that would allow a nice formula. I would guess that's because of the different kinds of acids found in wines which are all differing in strengths.


Also, I know there are conditions in which cold stabilizing (which precipitates out acid) can actually lower your pH. I read an explanation on that and it made sense, but I don't remember what that explanation was.

 

[Wade E]

Those #'s you listed 1st are I believe PH and not acid. The 1's below that are definitely acid and are what I go by all the time.

 

[geocorn]

They are acid number, just a different way of expressing them. Just multiply times 10 and all will look correct.

 

[suprasteve]

I didn't even stop to think of the different pH's ofthe same amount of differentacids in solution, oops, guess that makes quite a bit of spread! I guess I'll figure the higher pH for a lower TA and hopefully that should be close enough, better than strips I suppose. So in the neighborhood of a 3.5 for fruit wines I'm guessing and closer to 3.0 for, say sweet grape wines? Kinda been tasting it to get a mouth feel of what seems right and have been fairly consistently in the upper 3's by the strips if that means anything...

 

[JWMINNESOTA]

suprasteve, pH and titratable acidity are two different test. Think of it like this, T.A. is the measure of HOW MUCH (or Little) acid is there, While pH is the measure of HOW STRONG (or weak)the acid is. Usually the higher T.A. will be reflected by lower pH, but not always, as lower T.A. will usually be reflected as Higher pH, but not always. Depending on How strong(pH) and how much (T.A.) acid is present in the solution.

 

[grapeman]

The pH is a measure of how acidic the wine is. The lower the pH, the stonger the acid (probably oversimplified). The TA is a measure of the total amount of acid of that strength there is in g/L and like George says a figure of 0.80% is the same thing as a TA of 8 g/L. Generally speaking if you have a high TA, the pH will be lower. You can however sometimes have a good low pH of say 3.2 and still have a fairly low TA so it is best to measure both.

 

[gaudet]

Please correct me if I am misunderstanding this.

Knowing a little about pH:

pH is the measure of the strength of an acid or a base the lower the number (0-7) the stronger the acid.

TA is the total amount of all acids (citric, malic, tartaric) expressed in grams of acid per liter of solution.

So adding acid blend (or any of the individual acids) should bring down the pH (strengthen the acid)

We adjust accordingly before pitching yeast to ensure a good environment for yeast reproduction as well as taste/mouthfeel

 

[Dean]

Gaudet you are correct. However, different acids have different strenght at different concentrations. For instance, lactic acid is quite weak at 5% of volume, and acetic acid at 5% is stronger. Even stronger still at 5% of volume is hydrochloric acid, etc. Each acid that is stronger will have a lower PH, even though they will have the same amount of acid in g/L.

When it comes to wine, Citric is stronger than Malic which is stronger than tartaric. Citric really cannot be reduced except with precipitated chalk, malic can be turned into lactic and tartaric is the main acid we strive to be dominant in most wines.

While the two are related, PH and TA are very differnt things based on the strength versus amount.Edited by: Dean

 

[grapeman]

Any easy way to convert TA into a pH, like a simple formula, or is it just one of those low TA means high pH things with no clear answer?
Thanks!

After all of the above repies, I would have to say the answer to your question is NO

 

[Travisty]

Any easy way to convert TA into a pH, like a simple formula, or is it just one of those low TA means high pH things with no clear answer?
Thanks!

After all of the above repies, I would have to say the answer to your question is NO

Good answer!


Another way to think of it is that pH is a measure (on a logarithmic scale in which the lower number means a higher concentration of hydrogen ions) of the concentration of the hydrogen ions in solution. A stronger acid will disassociate it's hydrogen ions (or put more into solution) to a greater degree than a weaker acid so the stronger acid will have a lower pH thanthe weaker acid at the same molecular concentration. TA measures the total amount of acids. The acid/base reaction that takes place will measure all the molecular acid even if it hasn't disassociated its hydrogen ion(s).


So, say you have two different solutions with the same concentrations of two different acids (ie: One solution of tartaric acid at 6 g/L and one solution of malic acid at 6 g/L) the TA should be the same for each, but the pH should theoretically be lower for tartaric acid than for malic acid because tataric is a stronger acid than malic.

 

[suprasteve]

well darn, I was hoping for a quick and easy answer

points all well taken, thanks a bunch! One final question though, obviously a pH meter measures pH, the test strips as well measure pH I assume, the instructions on the acid titration kit refer to percentage acid in solution (TA), but since it uses phenolphthalein as a pH indicator, isn't this also really a measure of pH? So the only real way to measure TA is.... to measure it out exactly before pitching it in? And you never know exactly how much acid or in what quantities are in the must to begin with.


Or shouldI just say "yeah, somewhere from 3.0-3.5 pH should usually be close enough" and quit thinking about it so hard?

 

[Travisty]

The test for titratable acidity (TA) is an acid/base titration using phenolphthalein as an indicator, which changes color at a pH of 8.2, which happens to bethe point in this particular titration where all the acid has been neutralized by the sodium hydroxide (NaOH). You then can calculate how much acid is in the solution because you know exactly how much NaOH was added.


Basically, yes pH and TA are related, but the relation is not a linear one due to the different acids possibly in solution and the different strengths of all these acids. If there was only one acid ever in a must and all other conditions (ionic strength, temperature, etc.) were always the same, we might be able to reliably and accuratelyconvert TA to pH and vice versa. That's just not the case though, so you really can't convert TA to pH accurately. Just try and remember that pH is basically only a measure of the acidic strength of the must/wine whereas TA is a measurement of the amount of acid in the must/wine regardless of the strength of the acids dissolved in the wine.


As far as I know a pH of 3.0-3.5 will almost always give you an acceptable TA as well. IMO, I would rather have TA numbers than pH if I had to choose but I have very little evidence to say that's more than a personal preference!


Basically, you can get as deep into the chemistry as you want or you can simply follow the instructions and recipes and guidelines for winemaking and I'd be willing to bet youwill get great wine either way! I just happen to be a chemistry nerd and so I like to know more about the chemistry of winemaking, but that's definitely not a requirement for a home winemaker. In fact it could be a detriment sometimes! haha

 

[suprasteve]

I just happen to be a chemistry nerd and so I like to know more about the chemistry of winemaking

ha ha, seems I'mtrying to fall in that category as well! As an aside, I did end up just checking the pH in my secondaries and they all were in that 3-3.5 range, so I guess that's good. The titration makes sense, so I guess that's the only 'true' way to measure TA I have readily available, anyways thanks again for the responses!


EDIT: was bored today, searching the forum, found this:

"If you are going to get a pH meter, you can place the Acidometer on the shelf with the other little used equipment. First put your sample in a 50ml beaker and take your pH reading (the meter must be calibrated first). Then to determine acidity, slowly add sodium hydroxide (using burette, pipette or syringe), stirring as you add, until you have a pH reading of 8.2. The titratable acidity of your sample can thenbe determined with the following formula:<?amespace prefix = o ns = "urnchemas-microsoft-comfficeffice" /><?:NAMESPACE PREFIX = O /><?:NAMESPACE PREFIX = O /><O></O>

<O></O>
TA = 75 * V * C/VS<O></O>
<O></O>
Where:<O></O>
<O></O>
V = volume of sodium hydroxide needed to obtain a pH of 8.2<O></O>
C = concentration of sodium hydroxide used (0.1 normal or 0.2 normal)<O></O>
S = volume of the sample of wine or must<O></O>
<O></O>
For example: you have a 15ml sample of wine and add 12ml of 0.1 normal sodium hydroxide solution to reach a pH of 8.2.<O></O>
<O></O>
TA = 75 * 12 * (0.1 / 15)<O></O>
TA = 6.0<O></O>
<O></O>
The acidity of the sample is 6 grams per liter (6 parts per thousand or 0.60%). Note that this formula will also work if you use Phenolphthalein indicator solution since the color change occurs at pH 8.2
<O></O>
Play with the formula to adjust the sample and the concentration of sodium hydroxide solution. For example; if you use a 15ml sample and the concentration of sodium hydroxide is 0.2 normal, each ml of sodium hydroxide added translates into one gram per liter (0.1 %) of titratable acid.<O></O>

I should have thought of this! My issues with the TA test was the difficult-to-pinpoint transition of color. But if I take my same sample, add NaOH like i would with the phenol, but measure to 8.2 pH instead of relying on my eyes, it accomplishes the same thing! Just figured I'd add it here so the next person doesn't hafta find it 6 pages back Edited by: suprasteve