Titrations for total acid
Equipment:
Burette- 50 mlPipetteFunnelRetort Stand3 250 ml flasks or clear plastic cups45ml grape juice250ml .2M NaOH= 2gms of NaOH to 250ml distilled water Method:
Measure 15 ml of juice into each of 3 flasks or cups
Dilute to 150ml with distilled water
Add 7 drops phenolphthalein to each flask
Add 50ml of NaOH solution to burette
Titrate into juice until colour change is reached (end point)
Calculate %TA .
e.g 9ml = 9gms acid/100litre TA
Desirable level White wine 7-9Red Wine 6- 8
Accuracy
Make sure you read the burette at the low point of the meniscus.
The reading here is 4.8ml
pH Meter
A pH meter can be used instead if you wish as long as you are confident your meter is accurate.
The pH at which phenolphthalein changes colour is 8.2
Therefore adding 5ml quantities of NaOH (sodium hydroxide) and checking the pH change with a meter until the meter is stable at pH 8.2-8.4
CAUTION: This is very difficult to achieve with a hand held meter. They are not sensitive enough to small changes and tend to react suddenly to a gradual build-up of NaOH.
The amount of NaOH you have added to the wine sample is equivalent to the Total Acid of your wine.