Hi I've just bought two tests to measure TA in wine. However both tests rely on a colour change of the liquid . Due to me having a very deep red wine, I am unable to measure when the transition, even if I dilute it 50% with water.
Is there any other method?, or should I abandon the TA test altogether and relay on taste for acid content?
No don't abandon the test. It is really quite easy if you have a pH meter. The color change occurs when the pH reaches 8.2. Simpley add the NaOH as you normally do and at the same time stir and watch your pH. The end point occurs when the pH is 8.2. I know, it is not real intuitive that 8.2 is the end point instead of 7.0 but 8.2 is the point at which the indicator indicates neutrality. For more information, do a google on titration and
8.2. I used this method for the first time last week and it works like a charm.
Me too. I'm not color blind but most of my family is so we have used this for a while.
Thanks will try that out. A number is easier to read then a colour shade.
I'm not familiar with this test but the density of color in a red wine can be seen to change, if you put a yellow light behind the wine.
You need a burette for this test (a stir plate, and stir bar would be helpful but not necessary). Use .1N NaOH. First boil some D.I. water (adding some juice to the water can be helpful, but just a splash), to drive off any dissolved CO2. Adjust about 75 milliliters of this to a pH of 8.20. Add 10 mls of sample to the titration solution, and add .1N NaOH until you return to a pH of 8.20. Then multiply the number of mls of .1N NaOH you used, and multiply by .75 (another fudge factor). The results are expressed as grams of tartaric / 100 ml.
The pH is a better indicator of the sourness of the wine. The TA can be adjusted (by home wine makers) with the use of K2CO3 (potassium carbonate). Calcium carbonate could also be used but it may precipitate more tartaric than you want. Test in small batches first, and give it a couple of weeks to stabilize.
It's not 7 because you're neutralizing weak acids (acetic, tartaric, etc) with a strong base.
It's the isoelectric point of tartaric acid, where it isn't an ion, but still has both of its "acidic" protons attached.
No it isn't. Tartaric acid will have both of its acidic protons attached at a low pH; when you react it with sodium hydroxide in the titration, you're removing both of the acidic hydrogens.
Isoelectric points, as the link you provide indicates, are only relevant for amphoteric substances, such as metal oxides or amino acids. Tartaric acid is not amphoteric.
If you titrate a strong acid HX with sodium hydroxide, then at the equivalence point, all the acid will be converted to X-. Since HX is a strong acid, X- is a very weak base, and will not affect the pH of the solution. So the solution is neutral.
If you titrate a weak acid HA with sodium hydroxide, then at the equivalence point, all the acid will be converted to A-, which is a weak base. The A- anion will react with water via the reaction: A- + H2O HA + OH-. This means that there is a small amount of OH- in solution, and the solution is basic.
My bad, you're right.
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