Heat 10 ml of apple juice to 70oC in a test tube. Allow to cool then add 2-3 drops of
1% iodine in 10% potassium iodide solution (the type used for food tests). A blue colour
indicates the presence of starch; brown shows that the starch is partially broken down;
yellow indicates no starch.
have appreciable
amounts. A few tests of different varieties
will be needed.
Add 1 part of juice to 1.5 parts of acidified ethanol ( 96% pure alcohol to which 1%
concentrated hydrochloric acid has been added ). If flocculation occurs after 15 minutes,
pectin is still present.
3. Stability test
The clarified juice is heated to 75oC, cooled down immediately and kept for 4-6 hours
at 0oC in iced water or in a freezer. If no haze forms the juice is suitable for
concentrating or
bottling. If a haze forms
the juice requires further enzyme treatment.