Titrating for TA: using a pH meter to find the end point

I am no expert but I think you should Calibrate your PH meter with 2 buffers, PH 7 first and then PH 4. That way the meter can calibrate the slope correctly.

I agree. Some other comments:

I would measure the wine before heating it to get rid of CO2. You may have lost alcohol and or water during the heating which would concentrate the acids. The procedure I've heard is best is to measure the 15 ml of wine, heat and then restore the original volume using distilled water.

Andy

Andy:

Thanks for the reply. Yes, the wine was cheap and young, and didn't taste "acidy", so maybe the 4.3 measurement was not erroneous after all.

Maybe in order to remove the CO2 it would be better to subject it to vacuum than to heat it up, no?

Subjecting a wine to a vacuum will still lose fluids. Wonderful equipment you have! Sean

I also have a question. I've already add 50grams of tartaric to a Lodi Zin that had a pH of around 4.

I'm using 0.1N NaOH.

When I check the pH of the wine I got 3.49. I add 5ml of wine to a flask, add 50ml of distilled water and the pH reads 3.6. What gives? Shouldn't it be the same?

It took about 4.7 ml of NaOH to get to 8.2, so that's about .70 TA.

Igor wrote:

Nope. The pH should go up. And it went up by only as little as it did because wine is a pretty amazing buffer--it tends to resist pH changes.

Remember, pH is the negative log of the hydrogen ion concentration, so if you dilute the wine with water, you lower the concentation, and thereby raise the pH.

Dave

The procedure I follow is to collect a 50 ml sample; heat it, cool it back to the original temperature, restore the lost volume (which is almost always less than 2% of the original). Then measure both pH and TA.

To be honest most of the texts I have do not say it is necessary to heat the sample before measuring pH. I can tell you from experience that if there is any dissolved CO2 in the sample it will affect both TA and pH.

Joe

The Procedure you follow is all correct, heating the wine to degass it is fine, according "Techniques for Chemical Analysis and Quality Monitoring During Winemaking".

It is possible to dilute the wine with RO water for a TA without adverse effect. Again it reccomends it in the lab book, in order to ensure the pH meter electrode is covered, if using small amounts of wine.

Yes, as long as you measure the volume of wine before you subject it to heating or (reasonable) dilution you should be ok.

Andy