This section is from the book "Preserving And Pickling", by Mary M. Wright. Also available from Amazon: Preserving and Pickling: Two Hundred Recipes for Preserves, Jellies, Jams, Marmalades, Pickles, Relishes and Other Good Things.
Partially ripe grapes make better jelly than the ripe grapes. To every six pounds of grapes add three pounds of Siberian crab-apples, or apples, quartered. Stew all together until tender. Fill into a jelly bag and let drip into vessel. Measure the juice and to each pint of juice add one pound of sugar. Boil about thirty minutes before adding the sugar, then boil up after the sugar has been added. This should be ready to take off the fire in a few minutes, if the sugar has been heated in the oven before adding, but one should test it, and if it does not jelly, allow it to boil longer.
One-third of elderberry juice or one-third of rhubarb juice added to grape juice makes a nice jelly, with the flavor of grape.