TA vs pH

[Deezil]

Here's a noob question: do you need to measure acid (whether TA or pH) before fermentation begins, or is it OK to measure later on in the piece and make your adjustments then?

Much better to make the acidity adjustments pre-fermentation. Much better.

 

[REDRUM]

And if, er, that boat has already sailed ... would you recommend that acid adjustment be avoided altogether, or just try to err on the side of caution when adding any additional acids?

 

[vernsgal]

you can still adjust your levels after fermentation.I've read that if adjusting your TA after fermentation to use tartaric acid instead of an acid blend though.Or you could do a MLF which others here would have to explain.

 

[GeoS]

TA and pH are related and you adjust the SO2 based on the acid level so what your saying is correct. However, the SO2 that keep the wine from spoiling is the free SO2. That's the sulfur dioxide that has not bonded with the must. The only way to determine free SO2 is checking TA.

 

[cmason1957]

TA and pH are related and you adjust the SO2 based on the acid level so what your saying is correct. However, the SO2 that keep the wine from spoiling is the free SO2. That's the sulfur dioxide that has not bonded with the must. The only way to determine free SO2 is checking TA.

I don't believe the last part of this statement is true. Free SO2 has little or nothing to do with TA.

 

[GeoS]

You can adjust pH afterwards and may have to tweek it because pH will change during ferment.

Check TA at each stage to and add sulfite as needed but do not adjust acid based on TA.

MLF is converting harsh malic acid to a milder lactic acid and gives a buttery taste. Read up on this one and start a thread if you have questions.

 

[GeoS]

Cmason1957, then please enlighten us on this subject. Usually when giving a dissenting opinion one has justification for it.

 

[Deezil]

Cmason1957, then please enlighten us on this subject. Usually when giving a dissenting opinion one has justification for it.

SO2 additions are based off the current Free SO2 and the pH of the wine. TA is more about the taste perception, than anything else. You just have the two backwards is all;

I find in most instances, that pH relates more to SO2 additions, where TA usually relates more to peoples perception/taste of the wine.

pH is the important parameter for controlling spoilage bacteria and maintaining proper SO2 levels.

I believe that all the references you make to having the correct TA levels for SO2 should really refer to having the right pH value. The web citation you gave, for example, has a whole section on "The relationship between pH and SO2," and never mentions TA and SO2.

I don't believe the last part of this statement is true. Free SO2 has little or nothing to do with TA.

 

[ibglowin]

Sorry, free SO2 has nothing to do with TA.

I don't believe the last part of this statement is true. Free SO2 has little or nothing to do with TA.

 

[Bergmann]

OBEYWAN: you are whipping the wrong horse.

 

[berrycrush]

This article by Curtis Phillips helps clarifying the relation between SO2 and PH:

************************ from winebusiness.com **********************
...We frequently discuss a wine’s sulfite in terms of “free SO2” and “total SO2” because these are what we can measure. In wine, sulfur dioxide exists in several forms: dissolved sulfur dioxide gas, called “molecular SO2”; unbound bisulfite (HSO3-) or sulfite (SO32-) ions—the sulfite and bisulfite ions are in equilibrium and are usually lumped together with the molecular SO2 under the term “free SO2” or “unbound SO2”; bound bisulfite, where the bisulfite ion has formed a complex with something else, like acetaldehyde, sugars, uronic or ketonic acids. As one might expect, the “total SO2” is the sum of all of these forms.

From a winemaker’s perspective, it’s really the free SO2 that we pay attention to since it is easily measured whereas the molecular SO2 is not.

I find that a distressing number of winemakers overlook the detail that it’s the molecular SO2, not the free SO2, that provides protection from spoilage microbes. The amount of molecular SO2 that is in a solution depends on both the concentration of free SO2 and the pH of the wine. In simple terms, it takes roughly 10 times as much free SO2 to inhibit microbial activity in a wine with a pH of 4.0 than is needed in a wine with a pH of 3.0.

To put this back into terms of free SO2, we see that at pH 3.0 we need only 13.19 ppm free SO2 to achieve 0.8 molecular SO2, whereas at pH 4.0 we need a whopping 124.71 ppm free SO2 to get the same level of protection...
**********************************************************************************************

 

[GeoS]

Berrycrush, thanks. Very intresting, this article contradicts others I have read where they claim it's the free SO2 that prevents spoilage!

That certainly throws a wrench in the proverbial gear.....

Perhaps I am looking at this backwards. At least we're getting somewhere.

Adjust acid levels based on TA and adjust pH based on spoilage. What doesn't make sense to me is how do I tell how much potassium metabisulfite to add based on the pH?

 

[GeoS]

So I am backwards!

" An important consideration in sulfite management is that the effectiveness of free SO2 decreases as pH increases. Therefore, winemakers are advised to compensate for pH when managing the level of free SO2."

http://winemakermag.com/1301-sulfite-calculator

However, this article states it's the free SO2 that protects the wine.....

Now to find the mathematical relationship......

 

[sour_grapes]

Berrycrush, thanks. Very intresting, this article contradicts others I have read where they claim it's the free SO2 that prevents spoilage!

That certainly throws a wrench in the proverbial gear.....

Perhaps I am looking at this backwards. At least we're getting somewhere.

Adjust acid levels based on TA and adjust pH based on spoilage. What doesn't make sense to me is how do I tell how much potassium metabisulfite to add based on the pH?

It is not really in contradiction. "Free SO2" includes molecular SO2 as well as HSO3 and SO3:

Free SO2 consists of 3 species: molecular SO2 (directly active in preventing oxidation and spoilage), and two ions, HSO3- (bisulfite) and SO3= (sulfite), which comprise the majority of the free SO2 but are MUCH less reactive than molecular SO2. The percentage of free SO2 existing as molecular SO2 drops as pH rises (2nd column). Thus, at the SAME free SO2 level, wines with higher pH have less molecular SO2, and therefore less SO2 protection.

From http://www.santarosa.edu/~jhenderson/SO2.pdf


Think about it: If it were only free SO2 that mattered, we would not have to concern ourselves with pH at all!

Now to find the mathematical relationship......

Molecular SO2 = free SO2/[1 + 10^(pH – 1.8)]


Here is another good reference: https://www.extension.purdue.edu/extmedia/fs/fs-52-w.pdf

 

[ibglowin]

Easy Peesy.

Use the handy Winemaker Sulfite Calculator

Or use any of the charts.

Adjust acid levels based on TA and adjust pH based on spoilage. What doesn't make sense to me is how do I tell how much potassium metabisulfite to add based on the pH?

 

[GeoS]

Charts schmarts I use a calculator.....

Thanks sour_grapes.

 

[GeoS]

And I found an app for my note 4.....

 

[wineforfun]

Thanks Mike. Chart makes things easy to see.

 

[ibglowin]

Your very welcome.

 

[cmason1957]

Thanks all for jumping in and agreeing with me. I didn't get a chance to look at my phone all day long at work. I suppose I should have been a Lytle more explanatory there at the first.