How To Take An Acid Test With A ph Meter

[djrockinsteve]

How To Take An Acid Test With A ph Meter

Determining a wines acid titration can be difficult with a deep red wine such as Merlot or a Cabernet. Watching for the color change to a faint pink or gray end point can be challenging. However for those of you who have a ph meter, you are just a few steps away from determining your musts/wines acid percentage with 1 solution and in about half the time but with more accuracy.

Simply extract 10ml/cc of your wine with a syringe and place into a small cup. Rinse your syringe and draw 10ml/cc of Sodium Hydroxide (NaOh) solution (the same solution used in your acid titration kit but without the indicator solution-phenolphthalein) into it.

Now add 1ml/cc of NaOH to your wine sample and stir. I use the ph meter to stir mine. You will see the ph reading starting to rise. When it is complete you may record the reading or simply mark an addition of 1ml/cc.

Repeat by adding another 1ml/cc of NaOh to your sample and be sure to stir completely. The readings will start off rising slowly but later there will be a much larger increase. Wait until the reading stops and always indicate how much NaOh solution you’ve added.

Once you have reached a reading in the 8.0 area begin adding in increments of .2 or .25ml/cc of solution. You are to continue adding NaOH solution until your ph meter reaches a reading of 8.2 and stop. The above photo shows a reading of 8.02, just a few drops away from 8.2

All acid is neutralized at a ph reading of 8.2 Now that you have reached this reading or have come very close, count how much NaOh solution you have added. For example let’s say you added 8ml/cc of NaOh to reach a ph reading of 8.2 Simply multiply the number of ml/cc used (ex:8) times .75 (point 75) to give you your acid percentage reading. In this case it is .6% acid (point 6 %). You’re finished.

Immediately dispose of your sample and never return it or add these chemicals to your wine. Wash hands well if your skin comes in contact with them and rinse off your ph meter as well. Always store chemicals in a cool dark place and handle with care.

This is the same procedure used in your acid titration kit without the indicator solution and waiting for the wine to turn gray or pink. Now instead of purchasing two solutions phenolphthalein (indicator) and sodium hydroxide (NaOh) you need only one, sodium hydroxide.

For additional information about standardizing Sodium Hydroxide you may visit this page via the link,

http://www.extension.iastate.edu/Wine/Resources/preparingstandardsodiumhydroxidesolution.htm

courtesy of Bob F WMT Forum

 

[DoctorCAD]

Thats what I followed, but nowhere does it mention the .1N sodium hydroxide.

 

[djrockinsteve]

The .1N is what I have always used so I can't elaborate on the .2N solution. In fact I didn't know it existed for quite sometime as the single strength is all that my wine store carries.

 

[photoactivist]

Simply multiply the number of ml/cc used (ex:8) times .75 (point 75) to give you your acid percentage reading. In this case it is .6% acid (point 6 %).

Maybe this has to do with the 1N or 2N hydroxide you guys mentioned later; but my acid test says to multiply the cc's used by 0.25, not 0.75, to get the percentage tartaric. Are you sure you've got it right?
Either way, I'm super fascinated by this concept!

 

[wood1954]

I just did his test and it seemed to work, seems too easy. Sure is a lot easier than trying to use the color chart system

 

[JoP]

Maybe this has to do with the 1N or 2N hydroxide you guys mentioned later; but my acid test says to multiply the cc's used by 0.25, not 0.75, to get the percentage tartaric. Are you sure you've got it right?
Either way, I'm super fascinated by this concept!

Hi all,
The basic formula used to calculate TA as g/L of tartaric acid is as follows:
TA = (Vt * Nt *75)/ Vs
Where,
Vt: Volume of titrant in mL to acheeve the end point of PH 8.2
Vs: Volume of sample in mL
Nt: Titrant concentration in normality
75: Value based on various conversion factors (i.e. molecular weight, reaction ratio, etc.)
Vinmetrica’s simplified formula based on 0.133 NaOH titrant
Using NaOH 1.33 and 5 mL wine sample:
TA = (Vt * 0.133 *75)/ 5
The resulting simplified formula is:
TA = 2 * Vt
Example with 0.133 NaOH:
Let's say to achieve the end point of PH 8.2 you used 3.2 mL of titrant in a 5 mL of wine:
Basic formula:
TA = (3.2 * 0.133 *75)/ 5
This gives you a TA of 6.38 g/L, or 0.638% concentration of Tartaric Acid
The simplified formula:
TA = 2 * 3.2
This gives you a TA of 6.4 g/L, or 0.64% concentration of Tartaric Acid
If you use different concentration of NaOH titrant, 0.1 for example, you will use more titrant to achieve the end point (by a factor of 1.33)
Cheers!

 

[masic2000]

Cool, here is a link of someone performing the same acid test as mentioned above,

 

[wood1954]

https://www.hannainst.com/hubfs/006-finished-content/eBooks/Wine_TA_ebook_12_07_15.pdfheres a good link about ph, ta and how to measure it.

 

[Hic]

All acid is neutralized at a ph reading of 8.2 Now that you have reached this reading or have come very close, count how much NaOh solution you have added. For example let’s say you added 8ml/cc of NaOh to reach a ph reading of 8.2 Simply multiply the number of ml/cc used (ex:8) times .75 (point 75) to give you your acid percentage reading. In this case it is .6% acid (point 6 %).

That last sentence looks wrong. 8 x 0.75 = 6%, not 0.6% as stated.

 

[sour_grapes]

That last sentence looks wrong. 8 x 0.75 = 6%, not 0.6% as stated.

I am guessing the confusion arose from citing TA as g/liter vs. percent. Both are in common use. A value of 7 g/liter is equivalent to 0.7%.

 

[mrchrisjordan091]

The .1N is what I have always used so I can't elaborate on the .2N solution. In fact I didn't know it existed for quite sometime as the single strength is all that my wine store carries.

Perhaps that has something to do with the 1N or 2N hydroxide you stated later; nevertheless, my acid test advises to multiply the cc's used by 0.25, not 0.75, to calculate the percentage tartaric. Are you certain you're on the correct track?
In any case, I'm completely enthralled with this concept!

 

[TurkeyHollow]

Here's a link to calculate TA with adjustments for normality of acid:
https://www.vinolab.hr/calculator/titratable-acidity-en34

 

[mrchrisjordan091]

Perhaps that has something to do with the 1N or 2N hydroxide you stated later; nevertheless, my acid more test advises to multiply the cc's used by 0.25

, not 0.75, to calculate the percentage tartaric. Are you certain you're on the correct track?
In any case, I'm completely enthralled with this concept!

Thanks For Sharing your Thoughts.

 

[Monty Knapp]

I use the "Vintner's Best" Acid Testing Kit.
On the box it say's that "Vintner's Best" is a registered trademark of LD Carlson Co.
I've bought the kit on Ebay and at a local liquor store - a chain called "Friar Tuck's" - in their beer and wine making section.

This kit removes the need for any math or formula.
You draw a 15mm sample of wine and place it in a cup.
You then draw 10ml of the NaOH solution provided and add it to the wine as described in the original post in this thread.
When your pH meter reads 8.2, you look at the syringe and determine how much NaOH you added.

If you added 6ml, then the TA of the wine is 0.6%.
If you added 7.5ml, then the TA of the wine is 0.75%.
And so on.......

No need for the formula.
This works because the wine sample is 15ml and NaOH solution is a .2N solution.

Using the formula provided above:
TA = (Vt * Nt *75)/ Vs
TA = (6ml x .2N x 75)/15ml
TA = 90/15 = 6g/L = 0.6%

Or

TA = (Vt * Nt *75)/ Vs
TA = (7.5ml x .2N x 75)/15ml
TA = 112.5/15 = 7.5g/L = 0.75%