Alternative Test for Protein Tannic Acid Precipitation

2 Alternative Test for Protein (Tannic Acid Precipitation) 

This test takes advantage interaction of tannin and protein to form a visually apparent haze or precipitate. 

To 100 mL of suspect wine, add 5 mL of tannic acid solution. Interpretation Formation of pronounced haze (compared to a control) in treated sample is indicative of unstable protein. 

Folin-Ciocalteu reagent. This reagent is commercially available and, given the chemicals and time involved in preparation, is a worthwhile expense. Whether purchased or made from scratch (see procedure below), the reagent should have a definite yellow coloration with no hint of blue-green. To reoxidize older solutions of Folin-Ciocalteu reagent, add several drops of bromine and reboil under a fume hood. 

2 L round bottom boiling fiask equiped with appropriate reflux condenser 

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