This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
4. In jelly-making, when much water has to be added to the fruit, the juice must be boiled down to restore its natural composition. Long boiling may destroy the jellying property of the pectin. Therefore use as little water as possible, and avoid overcooking.
For further development of topics treated in this section see: -
Olsen : Pure foods. Ch. 13.
Goldthwaite : Principles of jelly-making. (University of Illinois bulletin, v. 11, no. 31, March 30, 1914.)
Snell: Household chemistry. P. 180, Pectin.
Norris : Organic chemistry. Pp. 320-327, Pectin.
Harris : Jellies, preserves, and marmalades. Florida State College for Women. Dept. of Home Economics. Extension bulletin No. 3.