Wednesday, February 08, 2006
One of the simplest and most effective ways to measure T.A. in wine is by the titration method, which uses an inexpensive titration or acid test kit. These test kits can be purchased for as little as $6.00 and can be used over and over again.
If you took chemistry in high school, you'll probably remember that titration is a process where you determine the concentration of an unknown substance in a liquid (in our case, we are looking for the amount of acid in must or wine) by slowly adding a small amount of reagent (a base called sodium hydroxide - NaOH - whose chemical concentration is known) until a change in color occurs due to the presence of an indicator (phenolphthalein).
To begin the test, you will draw a 15 cc sample (one cc equals one ml) of must into a test tube. Most test tubes that come with the acid test kits are marked with a line indicating this volume. If not, no sweat. Just use a small plastic syringe (provided) to precisely measure the desired amount into the test tube, and be sure to rinse the syringe afterwards.
Next, put about 3 drops of phenolphthalein indicating solution into the test tube. Swirl or shake the test tube so the indicator is mixed in with the must.
Using the syringe, draw out 10 cc of reagent (sodium hydroxide), making sure there are no bubbles in the liquid. Be careful to avoid contact with your skin or eyes. This NaOH stuff burns something awful!
Very carefully, add the sodium hydroxide to the test tube 0.5 cc at a time. After each addition, swirl or shake the test tube to mix the contents together. You'll notice that the color of the liquid will momentarily change upon the addition of reagent. If you are testing white wines, the color change will be pink; if testing reds, the color change will be gray. Just swirl and swirl until the color subsides. So long as the color of the must goes back to the original color, repeat this step until the color change is permanent.
When the color (either pink or gray) DOESN'T go away, stop and determine the amount of reagent used. From here, it is very simple to determine the acidity of your must. For each cc of reagent used, this equals 0.1 % TA.
For example, if you used 6 cc of sodium hydroxide to react with the must, the titratable acidity of your must is 0.6 %.
Pretty simple, eh? Just remember to throw away your sample, since this stuff is toxic. DO NOT add it back into your must or wine.
Lastly, wash and dry your test equipment before storing it away.
Article from Grapestompers