NOTES ON DETERMINING

NOTES ON DETERMINING

THE COLOR ENDPOINT

WHEN TESTING FOR

TITRATABLE ACIDITY

IN RED WINES

The color compounds in red wine turn to green as NaOH (titrate solution) is added, so the phenolphthalein (color indicator) endpoint

must be perceived through the green color.

If the wine is very old or has browned, the sample may turn brown instead of green.

If the wine is very young, the sample may turn gray instead of green.

Each red wine will exhibit a different range of shades during the titration.

The color endpoint is indicated as the INTRUSION OF A PINKISH TINGE AFTER THE INITIAL REDDISH COLOR OF THE WINE HAS BEEN COMPLETELY REPLACED BY GREEN, BROWN OR GREY.

If using a pH meter, this color endpoint is pH 8.2.

HELFUL HINTS:

Use a white background and a bright white light.

Add about 200 mls of distilled water. Add color indicator. Add titrate solution until seeing the faintest pink (pH 8.2). Then add your sample and titrate.

Use boiling water to drive off CO2 in just fermented or effervescent wines.

Use a 500 ml or larger flask or beaker with as wide a bottom as possible.

.1N or .067N NaOH solutions are more accurate. Size of sample changes.

A buret is a much more precise way to dispense the titrate solution.