A question about using a pH meter to check the TA

[BernardSmith]

I thought I posted this question yesterday but I don't see it: Ive been reading how to use a pH meter to check the TA of a wine (It is easier to read the scale on a meter than it is to determine that an appropriate color change has occurred especially but not only when testing red wines) but I have also seen some videos on YouTube where the advice is to dilute the sample of wine with a quantity of distilled water before titrating NaOH. What is the reason for adding distilled water? Is it to allow you to use less sodium hydroxide to reach a pH of 8.2? But wouldn't using say, 15 mil of wine or 10 mil rather than 25 have a similar effect? Why add (distilled) water?

 

[ibglowin]

Water doesn't have any Tartaric acid so you can dilute the wine without changing the pH (to a point). The reason to add is so you need less wine (sample) to fully immerse the pH probe in. Less sample is less wine wasted!

 

[MalvinaScordaad]

Without getting into the chemistry equations adding water makes a bigger sample and easier to see. Also it depends on the strength of the Naoh Solution you are using. For example using a 0.1n solution you use 5 ml of wine to 100 ml of distilled water. There are Winemakers who use different strength Naoh and have to adjust the sample accordingly and use a different equation to calculate after getting to 8.2. When using 15 ml of wine and a 0.2 Naoh you start with 10 ml of Naoh and each ml used to get to 8.2 equals 1gr/liter of Acid. To me it is easier to use and work with a 100ml sample especially with the probe of the ph meter.

 

[whackfol]

I have found adding a couple of drops of wine to the distilled water and then titrating back to 8.2 pH before adding the wine sample improves my readings. Also, once you hit 8.2 in your titration you can just add a new sample to the old, now neutralized, liquid and re-titrate over it. I take three tests of each wine to confirm accuracy and repeatability. This saves time. I dilute so I have sufficient sample size to keep the probe submerged and allow enough clearance for the stirrer.

 

[GreginND]

Whackfol, what do you think the wine at the beginning is doing to make your readings more accurate? I would think just titrating the water to 8.2 and adding the wine would be the same.

And thanks for the tip on re-titrating samples. It never occurred to me but makes sense.

 

[winemaker_3352]

Without getting into the chemistry equations adding water makes a bigger sample and easier to see. Also it depends on the strength of the Naoh Solution you are using. For example using a 0.1n solution you use 5 ml of wine to 100 ml of distilled water. There are Winemakers who use different strength Naoh and have to adjust the sample accordingly and use a different equation to calculate after getting to 8.2. When using 15 ml of wine and a 0.2 Naoh you start with 10 ml of Naoh and each ml used to get to 8.2 equals 1gr/liter of Acid. To me it is easier to use and work with a 100ml sample especially with the probe of the ph meter.

Is this the equation you use?

Put 100 ml distilled water into 250 ml beaker w/ stir bar
Put 5 ml wine into water
Place pH meter probe into sample
Titrate with 0.10N NaOH to pH = 8.2
Multiply volume of NaOH used by 0.15
Result = percent TA

 

[whackfol]

To begin, I am not a chemist. So I am not the best to explain the reason. My procedure it one I have used for over ten years and, while I can't say exactly who suggested it, I believe I learned it at a wine lab seminar. It is my memory that it was recommended because: 1) The pH of pure water is very difficult to measure as it lacks buffering capacity with little or no mineral content. Try to measure the pH of pure water or a new bottle of distilled water. Mine drifts all over the place. 2) Distilled water absorbs CO2 from the air from the time it is distilled until you use it. Disolved in distilled water, CO2 forms carbonic acid. When you combine the sample of wine with the slightly acidic water, you are not accurately measuring the pH of the wine sample. I add the wine first so I create a better buffer in the water and also have something to titrate against.
Absent my lack of chemistry skills, I can vouch for the results I achieve. I have sent out over 30 samples over the years to an acredited lab and my results are always within .05 g/L. The same with pH, although I'm closer there. Best of all, my results are repeatable as I test each wine three times. If I find an outlier, I start again and examine everthing from my pH meter calibrations, the correct size of my pipette, normality of my NaOH...

 

[ibglowin]

TA in g/l = (A X B)/C

A = ml of NaOH used
B = Normality of the NaOH solution used
C= ml of must or wine sample

 

[ffemt128]

When using the formula of (V)(N)(75)(100)/1000(v) where

V=Volume of Sodium Hydroxide
N-Normality of Sodium Hydroxide (.1, .2)
v=volume of sample

If you are adding 100 ml of distilled water and 5 ml of wine, how would that affect the formula? Would you end up using more or less NaOH and what would the value of v be? Would it be 5 or 105?


I've never added distilled water when checking and wanter to confirm this.

Thanks,


I believe I found the above formula here on the site somewhere or maybe morewine.com

 

[ibglowin]

V= volume of wine used, not total volume of sample.

 

[winemaker_3352]

TA in g/l = (A X B)/C

A = ml of NaOH used
B = Normality of the NaOH solution used
C= ml of must or wine sample

So dumb question - what is the Normality of the NaOH solution? Does this need to be calculated?

 

[ibglowin]

It is listed on the bottle. Usually its 0.1 or 0.2 sometimes. Normality is basically the "strength" of the solution.

 

[ibglowin]

When carbon dioxide dissolves in water it exists in a chemical equilibrium producing carbonic acid:

CO2 + H2O --> H2CO3 --> H20 + CO2

Carbonic acid forms two kinds of salts, the carbonates and the bicarbonates. It is a weak acid.

To begin, I am not a chemist. So I am not the best to explain the reason. My procedure it one I have used for over ten years and, while I can't say exactly who suggested it, I believe I learned it at a wine lab seminar. It is my memory that it was recommended because: 1) The pH of pure water is very difficult to measure as it lacks buffering capacity with little or no mineral content. Try to measure the pH of pure water or a new bottle of distilled water. Mine drifts all over the place. 2) Distilled water absorbs CO2 from the air from the time it is distilled until you use it. Disolved in distilled water, CO2 forms carbolic acid. When you combine the sample of wine with the slightly acidic water, you are not accurately measuring the pH of the wine sample. I add the wine first so I create a better buffer in the water and also have something to titrate against.
Absent my lack of chemistry skills, I can vouch for the results I acheive. I have sent out over 30 samples over the years to an acredited lab and my results are always within .05 g/L. The same with pH, although I'm closer there. Best of all, my results are repeatable as I test each wine three times. If I find an outlier, I start again and examine everthing from my pH meter calibrations, the correct size of my pipette, normality of my NaOH...

 

[whackfol]

Just realized this was answered by the time I posted... Sorry

Carbonic not carbolic -- got it! Thanks.

winemker 3352, that works! If you want a formula that allows for differing sample size and normality try this one:

TA (g/ml) = (ml NaOH)*(N NaOh)*(75)/10 * (ml of wine sample)

Go to Moundtop.com for a great discussion of testing procedures for TA and other tests. There are other articles on the site that I found informative.

 

[whackfol]

Knowing and verifying the normality of your NaOH is essential. You can verify the strength with a primary standard such as KaPH or a lesser standard such as HCl of a similar normality. I was taught to verify every time I test. You will find that even fresh NaOH will not be exactly the normality stated. That being said, I standardize my NaOH with phenolphthalein and, if I don't get the titration exactly right, I introduce an error.

 

[Ernest T Bass]

As Eddie would say, "here is a real dumb question". If the pH is good, 3.4 to 3.6, is TA really that important? I feel sure it is from all this discussion, but I don't understand why it's soo important if the pH is good.
Thanks for any replies
Semper Fi

 

[Runningwolf]

As Eddie would say, "here is a real dumb question". If the pH is good, 3.4 to 3.6, is TA really that important? I feel sure it is from all this discussion, but I don't understand why it's soo important if the pH is good.
Thanks for any replies
Semper Fi

Bud if the acid is real high, it is not drinkable to a lot of people. In some cases high acid can be countered by having a high rs in your finished wine.

 

[ibglowin]

pH and TA are related but you can have one good and one out of whack. You have to test for both!

 

[MalvinaScordaad]

Is this the equation you use?

Put 100 ml distilled water into 250 ml beaker w/ stir bar
Put 5 ml wine into water
Place pH meter probe into sample
Titrate with 0.10N NaOH to pH = 8.2
Multiply volume of NaOH used by 0.15
Result = percent TA

That's it!
Malvina

 

[MalvinaScordaad]

Knowing and verifying the normality of your NaOH is essential. You can verify the strength with a primary standard such as KaPH or a lesser standard such as HCl of a similar normality. I was taught to verify every time I test. You will find that even fresh NaOH will not be exactly the normality stated. That being said, I standardize my NaOH with phenolphthalein and, if I don't get the titration exactly right, I introduce an error.

Didn't you mean potassium acid phthalate?
Malvina