# Total Acidity Question ### Help Support Winemaking Talk - Winemaking Forum: #### JeremyBenson11

##### Junior
I'm looking at two different articles for calculating total acidity, without any scientific background and a lack of math skills one is a bit harder. I was wondering the more scientific method is vastly different than the second method. The second method is the simplified NaOH method with and without pH meter. I assume the harder method is more accurate? I'll show both below.

First Method:

15 ml sample titrated out with 12.6 ml of the 0.1 molar solution of sodium hydroxide (NaOH).

1. Calculate molar mass of acid in sample as sum mass of all atoms in the melucule.
- The molar ass of Tartaric Acid:
(C4H6O6)=4 x M(C)+6 x M(H)+6 x M(O)=4 x 12+6 x 1+6 x 16=150 g/mole.
150 g/mole.

2. Caluclate number of moles of NaOh by multiplying volume of NaOH by its concentration.
Number of moles = Volume (in L) x molar (mole/L) concentration.
number of moles (NaOH) = 0.0126 L x 0.1 mole/L= 0.00126 moles.
0.00126 moles.

3. Divide moles of acid by sample volume and multiply by 100 to find acid amount in 100ml.
(C4H6O6) = 0.00063 moles x 100 ml/15 ml = 0.0042 moles.
0.0042 moles.

4. Multiply the acid amount in 100 ml (Step 5) by its molar mass (Step 1) to calculate titratable acidity (in g/100 ml).
titratable acidity = 0.0042 x 150 = 0.63 g/100 ml.
0.63 g/100 ml.

Second Method:

Calibrate the pH meter using a two point calibration. The most common buffer solutions used for calibration are pH 7 and pH 4 but pH 10 is also available. Our pH meter has two set screws with one marked pH 7 and the other pH 4 or 10. Fresh pH buffer solutions are important to assure accuracy in the calibration of the meter.

First, calibrate with pH 7 buffer because this is a weaker solution. If the meter does not read pH 7 with the pH 7 buffer, we turn set screw marked pH 7.0 to attain 7.0.

Then calibrate with the pH 4 buffer solution turning the set screw marked pH 4, or whatever method used for your meter.

Add a known amount of grape juice or wine into a beaker (usually 10 milliliters).
Place the pH meter into the solution. At this point you can take a reading of the pH of the must or wine.

Add 0.1N NaOH (1/10 Normal Sodium Hydroxide) to the solution until the pH meter reads 8.2. In our set-up, we have a stand that supports a 10 ml burette with a stopcock on the bottom of the burette. The burette is calibrated in 0.1 increments. When the stopcock is opened, the solution is allowed to flow into the beaker. Closing the stopcock stops the flow of solution and allows a reading from the burette of how much solution has been dispensed. As the solution pH rises to around a pH of 6.0, changes occur faster so be careful as you pass pH 7.0 on your way to pH 8.2.

Use the following formula to determine the TA of your wine or must. 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.

#### sour_grapes

##### Victim of the Invasion of the Avatar Snatchers
I'm looking at two different articles for calculating total acidity, without any scientific background and a lack of math skills one is a bit harder. I was wondering the more scientific method is vastly different than the second method. The second method is the simplified NaOH method with and without pH meter. I assume the harder method is more accurate? I'll show both below.

First Method:

15 ml sample titrated out with 12.6 ml of the 0.1 molar solution of sodium hydroxide (NaOH).

1. Calculate molar mass of acid in sample as sum mass of all atoms in the melucule.
- The molar ass of Tartaric Acid:
(C4H6O6)=4 x M(C)+6 x M(H)+6 x M(O)=4 x 12+6 x 1+6 x 16=150 g/mole.
150 g/mole.

2. Caluclate number of moles of NaOh by multiplying volume of NaOH by its concentration.
Number of moles = Volume (in L) x molar (mole/L) concentration.
number of moles (NaOH) = 0.0126 L x 0.1 mole/L= 0.00126 moles.
0.00126 moles.

3. Divide moles of acid by sample volume and multiply by 100 to find acid amount in 100ml.
(C4H6O6) = 0.00063 moles x 100 ml/15 ml = 0.0042 moles.
0.0042 moles.

4. Multiply the acid amount in 100 ml (Step 5) by its molar mass (Step 1) to calculate titratable acidity (in g/100 ml).
titratable acidity = 0.0042 x 150 = 0.63 g/100 ml.
0.63 g/100 ml.

Second Method:

Calibrate the pH meter using a two point calibration. The most common buffer solutions used for calibration are pH 7 and pH 4 but pH 10 is also available. Our pH meter has two set screws with one marked pH 7 and the other pH 4 or 10. Fresh pH buffer solutions are important to assure accuracy in the calibration of the meter.

First, calibrate with pH 7 buffer because this is a weaker solution. If the meter does not read pH 7 with the pH 7 buffer, we turn set screw marked pH 7.0 to attain 7.0.

Then calibrate with the pH 4 buffer solution turning the set screw marked pH 4, or whatever method used for your meter.

Add a known amount of grape juice or wine into a beaker (usually 10 milliliters).
Place the pH meter into the solution. At this point you can take a reading of the pH of the must or wine.

Add 0.1N NaOH (1/10 Normal Sodium Hydroxide) to the solution until the pH meter reads 8.2. In our set-up, we have a stand that supports a 10 ml burette with a stopcock on the bottom of the burette. The burette is calibrated in 0.1 increments. When the stopcock is opened, the solution is allowed to flow into the beaker. Closing the stopcock stops the flow of solution and allows a reading from the burette of how much solution has been dispensed. As the solution pH rises to around a pH of 6.0, changes occur faster so be careful as you pass pH 7.0 on your way to pH 8.2.

Use the following formula to determine the TA of your wine or must. 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.

As I read it, the first method merely reveals the thinking behind the second method.

But there is an important question/distinction: What is meant in the first method by "15 ml sample titrated out with 12.6 ml of the 0.1 molar solution of sodium hydroxide (NaOH)"? Titrated to what? If to a fixed pH value, then I become more sure of my first comment. But without knowing what is meant by this step, the first "method" is not really a method!

#### JeremyBenson11

##### Junior
I would think that statement means 15ml of wine, say, meeting its final sodium hydroxide reaction at 12.6 ml of sodium hydroxide?

#### sour_grapes

##### Victim of the Invasion of the Avatar Snatchers
I would think that statement means 15ml of wine, say, meeting its final sodium hydroxide reaction at 12.6 ml of sodium hydroxide?

Well, why 12.6 ml? What if you added 43 ml? Or 78 ml? The first method would indicate a different TA in each of these cases. (Which is obviously wrong.)

We need to know what the criterion is that determines how much NaOH solution to add. (I am willing to bet it is to get to a certain pH value, likely 8.2.)

#### JeremyBenson11

##### Junior
Well, this is what I think I know. You add 0.1N sodium hydroxide to a 15ml sample of any liquid until there is no more reaction. So you wouldn't add 12.6, or 43ml, or 78ml. You would add sodium hydroxide until adding it is complete based on final reaction. I think, in this case, that amount as 12.6ml.

#### ibglowin

##### Moderator
Staff member
Super Moderator
Two ways to get TA in wine. One is with a pH meter and you titrate your sample to pH 8.2.

2nd is the old school way using an indicator (in this case phenylthalene) which turns color (indicating the titration endpoint) at....... pH 8.2

The formula (for TA) will vary depending on your (wine) sample size, and strength of your NaOH (titrant).

See this (old) thread: When testing acid and ph with a meter, how much

Last edited:

#### sour_grapes

##### Victim of the Invasion of the Avatar Snatchers
You would add sodium hydroxide until adding it is complete based on final reaction. I think, in this case, that amount as 12.6ml.

The question I have is how do you know the "final reaction" is "complete." As I have said, and as Mike has said, those directions probably mean that you add NaOH until the pH is 8.2.

May I suggest that you review the place where you got the directions for Method 1 to see if they tell you? Was it here: How to Calculate Titratable Acidity ? If so, this example directs you to use the phenylthalene indicator that Mike referred to (which, as he said, turns color when the pH is 8.2).

#### JeremyBenson11

##### Junior
That is the article sour_grapes. I can't find the word 'phenylthalene' in the article, can you quote the area for me? I see, other articles I read phenylthalene wasn't necessary, but was included to help. I had indications you could see the final reaction without it.

Thanks Mike, I understood that method, but I'm just trying to determine accuracy is all.

#### sour_grapes

##### Victim of the Invasion of the Avatar Snatchers
It is tacitly referred to here: "The reaction completetion [sic] is determined by a chemical indicator that changes its color at this point."

#### JeremyBenson11

##### Junior
I see. Thanks for the help. I have a second question about ABV. I've seen Brix - TA = ABV, but I find that hard to believe. Is that more of an estimate?

#### cmason1957

##### CRS Sufferer
Supporting Member
I see. Thanks for the help. I have a second question about ABV. I've seen Brix - TA = ABV, but I find that hard to believe. Is that more of an estimate?

TA has nothing to do with ABV at all.

A rough estimate, assuming that your must will ferment to 0 Brix, is Starting Brix * 0.59 = ABV.