Checking TA with a pH meter

[DoctorCAD]

I found a link that shows how to check TA by using a pH meter and sodium hydroxide. You add a few ml of the sodium hydroxide to the wine until a balance point at 8.2 pH is reached, and multiply the number of ml by 3/4 to get a percent TA.

OK, that is all well and good, but my readings are so far off of what I think they should be that something must be wrong.

My wine (and I tested 3, a Williams Pino Noir, a Williams Merlot and a Selection International Tempranillo w/grape pack) show that my pH's are a little bit low, somewhere around 3.35 to 3.55.

The TA readings are where I am messing up, if I add 4 ml, I get readings around 7.8ish, just a few more drops shoots the pH up to well over 8.2., so that gives me a TA of 3% TA. That is about half of what I expected and the two numbers together (pH and TA) just seem to not be right.

One thing I noticed is that my sodium hydroxide is .2N. Is that where I am getting messed up?

 

[salcoco]

Yes, I am not sure what the multiplier would be if the titrator is.2, suggest using .1

 

[DoctorCAD]

I found this formula that allows all volumes and dilutions.

Here is the Equation for using any sample size and any strength NaOH.

TA as tartaric acid (g/100 ml) = (V) x (N) x (7.5) / v
If you want the answer in g/L you would multiply x 10

V = ml of sodium hydroxide solution used for titration
N = Normality of sodium hydroxide solution
v = sample volume (ml)

I used 10 ml of wine and appx. 4.25 ml of .2N sodium hydroxide

I my case you would have: 4.25 x (0.2) x (7.5) / 10 = 6.375/10 = .6375%
.6375 x 10 = 6.4g/l TA

Much Better!
Much better!

 

[djrockinsteve]

That's your problem. I have always used single strength. Calculate as its twice the amount. I believe that is accurate.

 

[djrockinsteve]

Here is a tutorial on getting an acid % with a PH meter.

http://www.winemakingtalk.com/forum/f71/how-take-acid-test-ph-meter-11244/

 

[LoveTheWine]

anybody use the wine calc app for this?

http://web2.airmail.net/sgross/fermcalc/FermCalcJS.html

it gives you the option to type in the sample size of juice and then the strength/amount of Sod Hydroxide used. It then spits out an answer.

Just wondering if its accurate or not.

 

[Hokapsig]

remember that when adding your NaOH, that pH is logarithmic. So when you get close to 7.8 and you're looking for 8.2, it will only take a few drops to get to the 8.2 reading. It's easy to blow right on by 8.2 which then will throw off your reading.

 

[Poni]

Try this calculator, you can type in the normality of the NaoH - http://web2.airmail.net/sgross/fermcalc/fermcalc_download.html

When i do these titration with my vimetrica, even though it is an awesome shiny vinmetrica unit, i still have to titrate slowly, and set the drip on the burette to a slow moderate drip. Sometimes when i get the pH to certain points like 5 6 and 7 i allow the ph meter to catch up from the titrations, stabilize and then slowly proceed to 8.2, the end point. it takes practice to reach the 8.2 end point smoothly without blowing past 8.2.