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.
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.
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.
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.
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
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
0.15.
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).
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.
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
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