Acid test using PH meter

Hello Pete, If this is happening in your white wine I would guess your pH meter is off. If this is happening in your red wine then it is the wine pigments changing with pH and not the endpoint. I use a pH meter instead of phenothaline because I screwed up a batch of pomegranate wine thinking it only had about .5 TA when it was much much higher. If you want to use a color indicator for red wine you need to dilute the red wine with distilled water.

-Alex P

coupla thots....

Are you using the 5-second rule? i.e. the color stays for 5 seconds before disappearing.

How old are your pH calibration buffers?

Gene

Pete,

Trust the pHep5 and forget about the phenolphthalein.

Turns color does not matter, _stays_ at the faint color change for several seconds does. The endpoint of phenolphlthalein is 8.0 - 8.4. If you are seeing it change before that the meter calibration or technique is supect.

Make sure you swirl well or stir well, it's not as tricky as it sounds. Red wines can interfere as said previously.

Calibrate the meter before each use, it's good practice. Some calibrate before and after, that way there is no question the meter is accurate.

The Europeans use 7 as the endpoint as an FYI.

Joe

Hi: Remember to heat the sample to boiling to drive off the carbon dioxide will interfere with the titration (it is acidic and will titrate) Cool to room temperature using a cover on the beaker so that the solution does not reabsorb carbon dioxide.

My color is staying at least five minutes. I just bought new buffer tablets this year. Same results from my old liquid tablets.

I have distilled water, what PH should I get with that?

gene wrote:

Maybe that is my problem.

The must was fermenting...

I have some still wine now... I am going to start taking another round of readings.

Joe Yudels> Hi: Remember to heat the sample to boiling to drive off the carbon dioxide

Depending on how much CO2 is absorbed, anywhere from pH 5.6 to 6.3. (equilibrium in contact with air tends to pH 5.6-5.8). Distilled water without pH buffers is not reliable as a pH reference solution.

Joe's advice is good.

Gene

Please remember that your "still wine" may be nearly saturated with carbon dioxide gas, so de-gassing your test sample may still necessary. Lum Del Mar, California, USA

Hi: Theoretically the pH of pure water should be 7. But this is rarely obtained with samples exposed to air (due to CO2 adsorption)

So if I check it in distilled water... I should be close to 7?

And the best way to de-gas is by boiling?

Won't this concentrate the wine, by driving off water?

Pete, there are several ways to de-gas your wine sample. Some are more accurate than others. Here is the one I prefer because it is easy.

(1) Accurately measure 5 milliliters of wine and place in a Pyrex flask. (2) Add about 50 milliliters of distilled water. (3) Place the flask in a microwave oven and bring the contents to a boil. (Turn off microwave as soon as bubbles are seen). (4) Cool the de-gassed sample to room temperature. (5) Titrate to end point with 0.1 N sodium hydroxide. (6) Obtain TA by multiplying the milliliters of sodium hydroxide used by

The exact quantity of distilled water added (or lost) is not important. You are measuring the amount of acid molecules contained in the 5 milliliters of wine. Pure water contains no acid, so the amount of acid in the flask is independent of the water added (or lost).

Lum Del Mar, California, USA

A saturated solution of potassium bitartrate has a pH of 3.56 at room temperature.

Buy "cream of tarter" at the grocery store. Add about 1/4 tsp. of the cream of tarter to a cup of distilled water and stir well. Let the solution sit over night.

The solution is saturated if you can see crystals on the bottom of the container and the pH will be 3.56. The solution will keep for a week or two.

Would the following be true? (rather than "Pure water contains no acid") :

Pure distilled water contains a small amount of carbonic acid solution [(HCO3- + H+) the ionized form in water] from the dissolved carbon dioxide. The amount of the carbonic acid in the degassed solution of wine and distilled water is small enough that it is an insiginificant contribution to your TA measurement.

milliliters of

You are correct Gene. Please pardon my slipshod explanation. Lum Del Mar, California, USA

Bring sample just to the very start of a boil. CO2 will have been driven off before any H2O is lost to speak of.

My acid test kit says to multiply by .25

Why do you suggest .15?

Just curious.

Lum wrote:

The correct value is 0.15 _if_ you are titrating a 5 milliliter wine sample with 0.1 N sodium hydroxide. Other values are needed if you use another size wine sample or if you use sodium hydroxide with some other normality. Lum Del Mar, California, USA