Difference between titrating for ppt and measuring pH of acid

[StringJunky]

A long time ago, I had a book on winemaking that delved into the chemistry more than most. It said, iirc correctly, that titrating wine was a more accurate/predictable  measure of how acidic the wine would taste than measuring pH. In those 80's days it was litmus paper tests or titrating. Titrating red wine was difficult to see the indicator result. 

Fast forward to now, I'm thinking of winemaking again and would like to use an electronic pH meter I have.

Does anybody understand the difference the author was talking about. The authors were chemists themselves.

Edited March 17, 2023 by StringJunky

[studiot]

titrating for ppt  ?

 

Can you elaborate on this  ppt only means power point to me.

 

I know little of winemaking chemistry, but understand that various measurements can be made as well as acidity.

The fruit contains sugars and fruit acids to start with.

These are fermented first to alcohols and then to vinegars by the action of the yeasts.

So chemical monitoring is more complicated than just measuring acidity.

 

[StringJunky]

9 minutes ago, studiot said:

titrating for ppt  ?

 

Can you elaborate on this  ppt only means power point to me.

 

I know little of winemaking chemistry, but understand that various measurements can be made as well as acidity.

The fruit contains sugars and fruit acids to start with.

These are fermented first to alcohols and then to vinegars by the action of the yeasts.

So chemical monitoring is more complicated than just measuring acidity.

 

ppt-parts per thousand. I'm just looking at this parameter. I'm fully aware of the intricacies of winemaking, but it's been a long gap and I remember that I didn't fathom this. I'll probably just buy the book again. I know a lot more now and will probably fall in to place anyway once I read it again.

[exchemist]

35 minutes ago, StringJunky said:

A long time ago, I had a book on winemaking that delved into the chemistry more than most. It said, iirc correctly, that titrating wine was a more accurate/predictable  measure of how acidic the wine would taste than measuring pH. In those 80's days it was litmus paper tests or titrating. Titrating red wine was difficult to see the indicator result. 

Fast forward to now, I'm thinking of winemaking again and would like to use an electronic pH meter I have.

Does anybody understand the difference the author was talking about. The authors were chemists themselves.

I assume the idea of titration is to determine the amount of acid present rather than just the pH. As there are several weak acids present in wine, the pH will tell you the concentration of H+, but that won't tell you how much of the acid molecules there are, since they are only partially dissociated and if there are several you won't be able to correlate an H+ concentration with the total amount of all of them.

But I'm guessing a bit.   

[StringJunky]

1 minute ago, exchemist said:

I assume the idea of titration is to determine the amount of acid present rather than just the pH. As there are several weak acids present in wine, the pH will tell you the concentration of H+, but that won't tell you how much of the acid molecules there are, since they are only partially dissociated and if there are several you won't be able to correlate an H+ concentration with the total amount of all of them.

But I'm guessing a bit.   

Yes, thanks. That sounds like it. I had a feeling it was to do with the fact that there is a detectable correlation in taste using titration but not pH. Is it likely that the H+ ion concentration does not correlate to taste differences? You have given me something  to make a start to look into. Thanks.

[studiot]

Here is a procedure for determining the acid content of a wine

 

[exchemist]

Just now, StringJunky said:

Yes, thanks. That sounds like it. I had a feeling it was to do with the fact that there is a detectable correlation in taste using titration but not pH. Is it likely that the H+ ion concentration does not correlate to taste differences? You have given me something  to make a start to look into. Thanks.

There are several acids: tartaric, citric, malic and maybe more. Tartaric and malic are dibasic and citric is tribasic. Each carboxylate group will have a different tendency to release H+ (different pKa). All are contributing to the overall H+ concentration. To make matters worse, you can get (as a winemaker you may indeed want) malolactic fermentation, which converts some of the malic acid into lactic acid, which is monobasic, with a fairly low pKa.

I imagine the mouth feel and perceived acidity of the wine may depend on how much of each is present. Since saliva is slightly basic, you could perhaps get a sort of buffering situation in your mouth. Quite complicated, I would think.  

[StringJunky]

3 minutes ago, studiot said:

Here is a procedure for determining the acid content of a wine

 

Thanks that will be useful but I didn't want to use indicator for visibility reasons. It turns out I can measure the endpoint with my meter.

Quote

https://www.awri.com.au/industry_support/winemaking_resources/laboratory_methods/chemical/ta/#pH

TITRATION TO END POINT USING PH METER
Description: The TA of grape juice or wine is determined by titration to an end point of pH 8.2 as indicated by a pH meter. Wine samples are degassed prior to measurement to remove dissolved carbon dioxide. The measurement is subject to temperature effects, due to both sample and instrument, and must be corrected, with most meters and electrodes having automatic temperature compensation.
Equipment: Burette for titration, pH meter, pH electrode, flasks and vacuum for degassing (or nitrogen gas for sparging)

Reagents: Sodium hydroxide solution
Calibration: Use standard buffer solutions, recommended daily or as per manufacturers instructions
Services: Electricity, wash up area
Space required: Small bench area

 

[studiot]

I have also found an electrochemical procedure for determining sulphite (added commercially as a preservative) in white wine, if you are interested.

 

1 minute ago, StringJunky said:

Thanks that will be useful but I didn't want to use indicator for visibility reasons. It turns out I can measure the endpoint with my meter.

 

Note what exchemist and my attachments said about there being other acids so a pH meter will not directly compare with what appears to be an industry standard using only tartaric acid.

Perhaps industry now has an ion selective electrode for tartrate.

Edited March 17, 2023 by studiot

[StringJunky]

8 minutes ago, exchemist said:

There are several acids: tartaric, citric, malic and maybe more. Tartaric and malic are dibasic and citric is tribasic. Each carboxylate group will have a different tendency to release H+ (different pKa). All are contributing to the overall H+ concentration. To make matters worse, you can get (as a winemaker you may indeed want) malolactic fermentation, which converts some of the malic acid into lactic acid, which is monobasic, with a fairly low pKa.

I imagine the mouth feel and perceived acidity of the wine may depend on how much of each is present. Since saliva is slightly basic, you could perhaps get a sort of buffering situation in your mouth. Quite complicated, I would think.  

Thanks for that. 

Yes, each acid contributes a different quality and mouth feel. Onlythe empirical discovery of tasting will find the optimal balance, then I can quantify it for future reference and consistency.

5 minutes ago, studiot said:

I have also found an electrochemical procedure for determining sulphite (added commercially as a preservative) in white wine, if you are interested.

 

 

Note what exchemist and my attachments said about there being other acids so a pH meter will not directly compare with what appears to be an industry standard using only tartaric acid.

Perhaps industry now has an ion selective electrode for tartrate.

Yes. Thanks. I remember from that book it mentioned about sulphite can be fed to the yeast in low doses to increase glycerol. He showed the chemical pathway the yeast use as well.

I don't expect it to be accurate. I know I'll be working with a lot of noise obscuring my targets. Tis life!

 

[StringJunky]

I've re-ordered the book. Progressive Winemaking by Duncan and Acton. Released 1968.

[John Cuthber]

The simple answer is buffering.
https://en.wikipedia.org/wiki/Buffer_solution
If you have 5 ppt of citric acid in one wine and 5ppt of citric acid and also 5 ppt of sodium citrate in another wine they will have very different pH values but (relatively) similar tastes.
Or, at least that's what I'm told about the tastes; I never checked.

[StringJunky]

1 hour ago, John Cuthber said:

The simple answer is buffering.
https://en.wikipedia.org/wiki/Buffer_solution
If you have 5 ppt of citric acid in one wine and 5ppt of citric acid and also 5 ppt of sodium citrate in another wine they will have very different pH values but (relatively) similar tastes.
Or, at least that's what I'm told about the tastes; I never checked.

Thank you. That's useful.