Tartaric acid, total acidity or titratable acid

[sjjan]

I have been asked by a Dutch wine association to test one of their wines for an article in their upcoming magazine edition. Seemingly, I have an analyser that can measure things like malic-, lactic, acetic- or total acid levels, but they also want to know specifically the tartaric acidity level in the wine. They will compare my results with the test results from one of the top labs in Germany. I want to do a good job, but I am confused now with their request for the tartaric acid level. My analyser measures total acidity, not tartaric acidity.

Total acidity is often expressed in grams/liter of tartaric acid. There is even this formula: TA = (Number or milliliters of NaOH / Number of milliliters of juice) X 0.75 The units for the TA in this calculation are: Number of grams of tartaric acid per 100 milliliters of juice.

So how important is it to know or measure the tartaric acid level apart from the total or titratable acid level in the wine? How is it measured on its own? (tartaric that is).


A picture taken of the anlyser I use to measure stuff.

 

[Rice_Guy]

* how important is tartaric? Really tartaric doesn’t matter! Your tongue responds to H+ and we want a number of how many H+ are in the beverage. My understanding is that France reports results assuming all acid is H2SO4. We in the states report as if all acid is tartaric. Reported numbers are easy to convert from one acid to another.
* it is useful to have a unit which measures how your mouth will sense acid since this is a predictor of how the sugar will balance (taste good).

1) Cabernet sauvignon
View attachment 72205
by the numbers your Cab has a high TA 1.02%, low pH 3.05, normal gravity 0.995; the two samples I put in for reference (California & Florida commercial wines) have a TA in the "normal" range.
opinion: (if I look at this as a grocery store beverage) for that high a TA the numbers would suggest that it should be sweetened to be in the orange band, however it isn't a very tannic flavor so the balance is good, transparent..clean, good flavor/ no off flavors (VA) so technically it is a well made wine. A guess is that you sourced a northern Cab for reference two juice buckets in the club were:

Cabernet Sauvignon, Chile 2020​

3.83​

1.085​

​

0.49%​

Cabernet Sauvignon, California 2019​

3.28​

1.090​

​

0.44%​

I suggested members try to get the TA to 0.65% if they were competing in state fair next year, you are balanced so ignore the "rules".
,,,,, RiceGuy

* looks like an optical measuring system, one of the vinters club members has a similar technology and is very happy with it, ,,,, especially how easy it is to clean it.
* your calculation should specify the normality of the sodium hydroxide, there are several concentrations available in the States and they seem to be specific to who sold the kit.

 

[sjjan]

* how important is tartaric? Really tartaric doesn’t matter! Your tongue responds to H+ and we want a number of how many H+ are in the beverage. My understanding is that France reports results assuming all acid is H2SO4.
* looks like an optical measuring system, one of the vinters club members has a similar technology and is very happy with it, ,,,, especially how easy it is to clean it.

Thanks! Yes, France deals in a different way with TA and tartaric acid than e.g. Germany. It seems hard to measure tartaric acid separately? I can’t find any information on how it is being measured. I found a very short article on tartaric acide here: Why is testing for Tartaric Acid important in winemaking? from which I cannot conclude so easily why it would be so important.

The analyser is indeed an optical instrument (photospectral). It is a great device and takes away a lot of uncertainty around the winemaking process. I have a simpler version of the analyser shown here in this video:

 

[sour_grapes]

I don't know how your optical spectrometer works, i.e., exactly how the reagents interact with various compenents to render a signature that can be measured optically. But, to answer your questions, it is useful to step back and discuss how acid testing is done traditionally. (I believe you know a lot of this already, but I will try to set it out for others.)

Traditionally, the acid in the wine is titrated with a base until a set pH value is reached. As @Rice_Guy alluded to, the base does not "know" which specific acid is providing the H+ ions that the base is titrating. You only get to measure how many H+ ions there were, not the source of them. (And, as you know, some acids provide 1 H+ per molecule, some provide 2 H+ per molecule, and some provide 3.)

So what do you do with this number? One way is to pretend that all of the H+ ions came from tartaric acid (since that is the prinicipal acid in grapes). Then you figure out how many g/L of tartaric acid would be required to provide that many H+ ions. (Another way would be to pretend, as they do in "l'Hexagone," that all the ions came from sulfuric acid.) Back to TA: I think you can see why all of these names could apply. Hey! We are measuring all of the acids (Total Acidity). Wait, no, we are measuring just the ions that were dissociated, and thus that can be titrated! (Titratable Acidity). And, hey, let's express these as if they were all from Tartaric Acid. No wonder it is confusing!

Now, in your device, there seems to be a way to measure WHICH acids are present, i.e., not just the H+ ions, but some marker that is sensitive to the rest of the molecule. But I could not find enough info on the CDR Wine Lab site to tell how it is done.

 

[sjjan]

I don't know how your optical spectrometer works, i.e., exactly how the reagents interact with various compenents to render a signature that can be measured optically.

How TA is measured by the analyser is found here: Total Acidity with CDR Winelab Analyzer - Wine Test

Before using this analyser I used the Vinmetrica tools, which worked great using (mostly) the titration method to find the results.

 

[sjjan]

Now, in your device, there seems to be a way to measure WHICH acids are present, i.e., not just the H+ ions, but some marker that is sensitive to the rest of the molecule. But I could not find enough info on the CDR Wine Lab site to tell how it is done.

How L-Malic Acid is measured can be read at the bottom of this page: Determination of L-Malic acid - CDR WineLab Wine Testing

 

[sjjan]

@sour_grapes: I just started out making wine, so consider me a beginner. I have learned a lot along the way but the first wine is still to be bottled (in the coming weeks). I have had issues along the way during fermentation and afterwards that had to be resolved. And the wine that is ready to be bottled tastes good!

So, the wine lab where the wine association has sent an exact copy of the wine sample that is also sent to me is called Weinlabor Klug (weinlabor is wine laboratory in German). See: https://klug-gmbh.de/images/aktuelles/Weinlabor/Klug_GmbH_Messe-Flyer-Preisliste.pdf
I think it is considered as one of the most outstanding wine laboratoriets in Germany and, of course, I want to deliver an accurate result to the magazine and wine association for the comparison.

They are requesting: total acidity, tartaric acidity, malic acid, lactic and acetic acid. I can deliver with my analyser: total acidity, malic-, lactic- and acetic acid but not tartaric. I am using the analyser only in our own wine cellar. Now that I cannot deliver exactly what was asked for, I have to come with a good reason or story

 

[Rice_Guy]

The key seems to be the sample tube with pre measured reagent. (Curious what chemistry and how much cost per test). The pipete looks to be nanoliter accuracy.

I don't know how your optical spectrometer works, i.e., exactly how the reagents interact with various compenents to render a signature that can be measured optically.
Now, in your device, there seems to be a way to measure WHICH acids are present, i.e., not just the H+ ions, but some marker that is sensitive to the rest of the molecule. But I could not find enough info on the CDR Wine Lab site to tell how it is done.

 

[sjjan]

An analysis can be made with the Nespresso coffee machine and its coffee cups. The Nespresso machine is offered relatively “cheap” into the market and the money is made (or initially was made) with the Nespresso cups. This analyser works a bit like that. It is offered into the market at a competitive price and the test kits (the Nespresso cups so to say) are where they make some money.

The test kits are sold per 10 or 100 tests and the price per test ranges from 2 to 3.5 US$. So, if you want to test for pH, TA, free SO2, total SO2, acetic acid, L-Lactic and L-Malic acid and alcohol by volume, you would have to pay approx. 25-30 US% to run these test. If I send them to a lab, I would pay more or less the same, but now I have the results instantly and do not have to hassle with sending samples out to a lab.

As for the sampling size, we use small plastic test tubes of 5 mL. Most of the tests mentioned above only require a sample of 25 to 50 μL, where 1 μL is 0,001 mL. The pipette is accurate from 10 to 100 μL, so the 100.0 is 100 μL at which is it set as seen in the picture, but we would normally set it to e.g. 25 of 50 μL and pull a sample.



So before getting this analyser we were doing some of our tests with Vinmetrica as follows: Available Tests - Airtable
Nowadays, we do all the tests with the analyser and none through titration of distillation (alcohol by volume) anymore and than to confirm the results through another method.

 

[sour_grapes]

The key seems to be the sample tube with pre measured reagent. (Curious what chemistry and how much cost per test). The pipete looks to be nanoliter accuracy.

Now that @sjjan taught me that you have to scroll down on the pages to find this information , it appears that most of the analyses use the presence or absence of NAD+ vs. NADH. That is, they oxidize the analyte and convert NAD+ to NADH (or vice versa). The conversion is done with an enzymatic catalyst, so they get specificity to the particular analyte of interest. They have an optical absorbance test in the near-UV that is sensitive to NADH.

But they don't appear to have a enzyme for tartaric acid, I infer!

For total (titratable) acidity, they use a pH-sensitive dye, and detect the absorbance change (i.e., color change) upon titration optically.

 

[sjjan]

In the beginning I compared the results coming from my analyzer with that of an outside lab by sending a sample to an external commercial lab and the results were in my case spot-on. Yes, the tartaric acid measurement seems to be a difficult one. When asking them for the tartaric acid test, they (of course) answer that I don’t need it and that TA is more valuable.

So now that I cannot deliver on tartaric acid, I have to think of reasons why they won’t need it

 

[stickman]

I would just report the tests that your equipment is capable of, if you determine total acidity, you may then be able to just calculate the Tartaric acid by subtracting the malic, lactic, and acetic acid, but I'm not certain of the details, though I'm speculating you would have to convert the malic, lactic, and acetic numbers into their tartaric equivalent values before subtracting.
I noticed on some of my juice analysis certificates, the tartaric results have been indicated in some cases as determined by enzymatic method and other times indicated as HPLC.