Use caution when testing TA with ph meter

[REDBOATNY]

I tested two finished wines for TA this weekend using sodium hydroxide and a ph meter. I needed to make adjustments before cold stabilizing. The results were almost double compared to pre- fermentation. 1.5 compared to .9.

I suspected the sodium hydroxide and went to buy "fresh". The shop owner told me it only has a 6 month shelf life. When I returned home, I re-did the test and got what I expected .9 TA on Diamond, .85 on Niagara.

I then checked the PH of the old and new Sodium hydroxide and got readings of 11.4 /old, 14.6/ new.

Now the question: Is a PH test of the solution an accurate test of freshness?

 

[zadvocate]

Interesting I just bought new Sh and my results were similar. I need new again

 

[Runningwolf]

This is the procedure for checking Sodium Hydroxide

View attachment Sodium Hydroxide test.pdf

 

[ibglowin]

I am assuming you purchased either 0.1 or 0.01 Normal (N) NaOH from the Home Brew Store and not Concentrated (undiluted) NaOH. The stuff from your LHBS has been cut with water so in theory the 0.01N solution of NaOH has a pH of 12 and a 0.1N solution in theory has a pH of 13.

Unless you have a very very expensive pH meter you won't get much better accuracy than this on a typical inexpensive pH meter at extreme (low or high) pH's

Now the question: Is a PH test of the solution an accurate test of freshness?

 

[BernardSmith]

This is the procedure for checking Sodium Hydroxide

Can you use a pH meter (8.2) rather than the indicator to check for the amount of KaPH needed ?

 

[ceeaton]

This is the procedure for checking Sodium Hydroxide

Thank you for helping me solve one of my major issues with testing TA using NaOH. Nice that PI Wines had what I needed, ordered on Thursday night and had a box on my doorstep today before noon, very nice!

 

[ceeaton]

Just for giggles I tested my 0.2N solution tonight that I opened 10-29-16, it is now 0.185N. Tested the new 0.1N solution I had ordered from PI Wines and got 0.102N (pretty darn close, and I could have been a bit off with my syringe management (kids have had insulin pumps for some time now, no drawing for arm shots anymore, yea)).

Thrilled I can now test and trust my NaOH solutions, thank you Dan!

 

[bionerd]

xxxxxxxxxxxxx

 

[bionerd]

xxxxxxxxxxxxx

 

[jburtner]

We must always test the tester and calibrate the calibrator - Have a glass of wine and adjust the attitude

Cheers!
-johann

 

[ibglowin]

Actually the pH meter is the easiest and most accurate way to measure TA. Especially with red wine. You use a small amount of wine. Usually 10ml and then dilute it with distilled water (enough to cover the probe well) Usually 30-50ml or so. You can make your analysis more accurate if you bring your test water to pH 8.2 but your only talking about a drop or two of NaOH which is well within the noise of the analysis. Endpoint is 8.2 which is the endpoint of the Phenolphthalein indicator . Easy peasy with a pH meter.

Titratable Acidity Testing Kit Instructions

NaOH is hydroscopic, meaning that it will absorb water from the environment over time, which will cause the concentration of the solution to slowly decrease over time. If you notice the pH decreasing or you need to add more NaOH to titrate the same recipe, you probably need new NaOH. If you keep it properly stored (air tight container) it will last longer, but probably should replace every 6 month (more often if you expose it to air often)

pH is a direct measurement of the concentration of the concentration of the hydrogen ion concentration (which can be used to determine concentration of hydroxide). If you have a 1N solution of NaOH, it should give a reading of 14 on a pH meter. But you do want to make sure that you have properly calibrated your pH meter. Some meters only have calibration settings for solutions of pH of 7 and 4, which makes the meter more accurate for measuring low pH values, but not as accurate for large pH values. The other thing to consider if the pH scale itself. A pH difference of 1 unit equates to a 10 fold difference in concentration. So if you starting pH when you first bought your NaOH was 14 and now is 13, you have 10 fold less NaOH than what you started with.

For using a pH meter, you can, but you get the same results as using an indicator (long explanation of science below if you are interested)
You can use a pH meter for the titration, but this isn't really the easiest approach (I have done it both ways in lab). When using an indicator like phenolphthalein (the indicator that comes with most titration kits), it will change color once the solution gets to a pH around 8. Once you get to the equivalence point (where you have neutralized all your starting acid) the pH of the solution will quickly increase with additional base, which allows you to quickly see the change in color. If you were to do the titration with a pH meter, you would essentially be looking for the same rapid increase in pH. To accurately use a pH meter, you would likely need to use a larger volume of starting liquid to fully submerge the probe (and thus would use your NaOH solution more quickly). You would also need to constantly stir your solution (which you do anyway swirling the mixture when using indicator).

 

[Hoxviii]

Actually the pH meter is the easiest and most accurate way to measure TA. Especially with red wine. You use a small amount of wine. Usually 10ml and then dilute it with distilled water (enough to cover the probe well) Usually 30-50ml or so. You can make your analysis more accurate if you bring your test water to pH 8.2 but your only talking about a drop or two of NaOH which is well within the noise of the analysis. Endpoint is 8.2 which is the endpoint of the Phenolphthalein indicator . Easy peasy with a pH meter.

Titratable Acidity Testing Kit Instructions

You touched on this, but for this to work you need to know and trust your pH meter and know that when it indicates 8.2 it actually is 8.2. Using the pH meter and using 8.2 as a fixed end point means you have to use distilled water, correct that water to 8.2, de-air your must sample, and even then you need to watch for the sudden ramp up of indicated pH as you perform your test.

If you aren't doing all of that, then it really wouldn't be any more accurate than a visual titration. All you need to do for a visual titration is to make sure your hydroxide solution is still good per the PDF up thread, and watch for the color change.

So for someone that can verify their equipment I can see using the meter being a good method, but if someone has any questions about their equipment (or doesn't know 8.2 needs to be verified) I can see this as giving someone a false confidence/false sense of security. Ya know, a "the meter says 8.2 so it must be 8.2!" when there's no shade of pink showing.

 

[BernardSmith]

But trying to find color change with some red wines is not always very easy. The 8.2 is good enough even if not so accurate as long as you also trust your taste buds. Knowing the TA does not in fact mean that your wine is acidic enough or insufficiently acidic or too acidic

 

[ibglowin]

How do you see pink in a red wine sample?

Trusting your meter is sorta a given here and that is why you always calibrate with buffer solution(s) before hand. I would trust a pH meter any day of the week over a totally uncalibrated eye. Especially when your testing red wine samples. As I said the difference between uncorrected distilled water and corrected distilled water is one or two drops of NaOH. Considering your probably using a 5 or 10ml syringe that also is in the noise level of the syringe your using which more than likely has a 0.2ml increment.

 

[mikewatkins727]

This is the procedure for checking Sodium Hydroxide

Where, may I ask, do you get the Potassium Acid Phthalate?

 

[ibglowin]

http://www.piwine.com/potassium-acid-phthalate-n10-solution.html

Where, may I ask, do you get the Potassium Acid Phthalate?

 

[bionerd]

How do you see pink in a red wine sample?

If the color is dark you would want to dilute it with water till it becomes clearer. A 1:4 dilution would probably be sufficient. This wouldn't affect the amount of base that you need to add since you are still starting with the same amount of acid (just in a different volume).

With the dilute solution, the color change of phenylthalein should be really easy to see. It turns a vibrant pink. If you are worried about accuracy, using the same syringe would cause the same issues with the pH mediated titration. If you really want a good an accurate measurement, you should probably get a 1mL syringe.

Since it is an acid base titration, the pH should change really quickly with the addition of base to the solution after the equivalence point has been reached (you have neutralized all the acid). The color range change for phenylthalein is between 8 and 10, so it would occur right about when the pH is 8ish.

I tend to like using the indicator more simply because I dont trust the pH meter that I have. When I was doing titrations in the lab, I had access to a really high end pH meter that had .01 accuracy and was calibrated over a larger pH range. The one I have now is "student grade" aka bought with a just finished school budget. I would say if you have a fancy pH meter and feel comfortable using it, definitely go that route. But if you have a cheepo meter and wanna be sure you are getting accurate readings, indicator based endpoints are good too if you dilute the solution enough to see a strong color change.

 

[ibglowin]

I'm going to take a WAG in that you have never done single TA analysis on a sample of wine?

FYI, You can get a very accurate pH meter for about $100-150 these days. With temp probe compensation as well as 0.01 accuracy.

I have 35 years experience in analytical chemistry. You certainly can have have your phenylthalein if that is what you prefer. The rest of us will happily be using our pH meters and getting an accurate result without shooting past the endpoint in less than 2-3 minutes with some experience.

Oh and if you were to use a 1ml syringe you would have to refill it between 5 and 10 times for a single wine sample......

If the color is dark you would want to dilute it with water till it becomes clearer. A 1:4 dilution would probably be sufficient. This wouldn't affect the amount of base that you need to add since you are still starting with the same amount of acid (just in a different volume).

With the dilute solution, the color change of phenylthalein should be really easy to see. It turns a vibrant pink. If you are worried about accuracy, using the same syringe would cause the same issues with the pH mediated titration. If you really want a good an accurate measurement, you should probably get a 1mL syringe.

Since it is an acid base titration, the pH should change really quickly with the addition of base to the solution after the equivalence point has been reached (you have neutralized all the acid). The color range change for phenylthalein is between 8 and 10, so it would occur right about when the pH is 8ish.

I tend to like using the indicator more simply because I dont trust the pH meter that I have. When I was doing titrations in the lab, I had access to a really high end pH meter that had .01 accuracy and was calibrated over a larger pH range. The one I have now is "student grade" aka bought with a just finished school budget. I would say if you have a fancy pH meter and feel comfortable using it, definitely go that route. But if you have a cheepo meter and wanna be sure you are getting accurate readings, indicator based endpoints are good too if you dilute the solution enough to see a strong color change.

 

[bionerd]

I will say that i am not a total *****, I have a PhD (from the sciences and with that experience I'm pretty sure I know what a color change looks like). I'm here so that I can learn more about the process from other people, so you don't need to be condescending. I have gotten some great advice from other people that have been more welcoming and willing to have more of a conversation. I'm just saying that both can work. If you have a lot of money and want a super accurate process that's great, use your pH meter.

 

[Tnuscan]

At times I've wondered, if before electricity, if A/O might of still existed, but instead of an electric pump, like a bunch of guys blew into a little hose. When one was out of breath, the next guy tapped the shoulder of the guy waiting to blow next, then he took over, using a manifold of course.

I can just see these guys now, complaining about, how this little electric pump was going to put them all out of business.

Then along came the pH meter.

Edit: I use both, am I crazy or what? I'm waiting... @sour_grapes.