This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
Made of (1) 1 pt. water, 1/4 oz. pulverized alum, boiled a minute or two, 4 lbs. white sugar, boiled a short time, strained, colored variously, flavored with oils or essences to imitate fruit jellies. (2) 3 1/2 lbs. commonest gelatine in 2 1/2 gals, water with 30 lbs. sugar, boiled until gelatine is all dissolved, colored as desired, 1/4 oz. tartaric acid added, taken from the fire, dissolved, flavored, allowed to get cold in pails or glasses Makes 50 lbs. Glucose also is largely used in making bogus jellies, and the jams and preserves of the same class are made fruity with shredded turnips boiled in pineapple-flavored glucose. "A year or two since a man found himself with a large crop of red currants, and he manufactured them into "jam," or "jelly," using the best of sugar, and producing a most excellent article. He found the hotels supplied with a heap, impure article, manufactured from glucose and acids and colored to resemble somewhat in color and taste currant jelly, which could be procured at retail even lower than he could afford his at wholesale. The result was the enterprising man had a large quantity left on hand. But we haven't heard of his manufacturing any more 'pure currant jelly' for market.
A few years since a gentleman in Union village started the manufacture of apple-jelly, and he produced a very pure and delicious article, which should have commanded a ready sale at hotels, bakeries and in families, for the table and for pies, tarts, etc. But the business did not prosper, we think. At all events it was suspended. An inferior article, made up largely of adulterations, which 'answered the purpose,' took the trade".
An American physician teils how the cheap jellies which some bakers put into their tarts and jelly cakes are made, as follows: Take 4 qts. water and 1/2 lb. alum; boil 2 minutes, add 32 lbs. of white sugar; boil 5 minutes longer, strain while it is warm (and the hotter it is strained the easier) through a coarse towel; when nearly cold, add 2 ozs. of acetic acid, and 1/2 lb. of real currant jelly-When cool, pack it in tumblers. If you desire a vanilla jelly, add in place of currant jam four 25-cent bottles of extract of vanilla, and stir when nearly cold. If you desire strawberry jam, prepare the alum and sugar as before, and add 1/2 pt. of essence of strawberry. Or if lemon is desired, add essence of lemon. You can make what you like with these proportions of alum and sugar. " This is th way to make the grocers' jelly and jam that are placed in the confectioneries and bakeries".