Gelatin is made from ground-up animal by-products, including hooves and bones. According to Knox, the ubiquitous gelatin manufacturer, its gelatin, which comes in 7 gram/¼ ounce packages, will gel 2 cups of liquid. I find that one package of gelatin measures 2¼ teaspoons, so 1⅛ teaspoons are needed per cup of liquid.
Powdered gelatin needs to be softened in cool water for at least 5 minutes before being heated to dissolve it, a process that enables it to be effective as a thickening agent. Gelatin requires a minimum of 4 hours to thicken and will continue to thicken a mixture over a 24-hour period. Once it has reached maximum thickness, it will not thicken more, even on freezing, but neither will freezing affect its thickening power. A gelatin mixture can be frozen, thawed, remelted, and refrozen several times before it loses its thickening capability. I use Grayslake powdered gelatin, available at cake decorating and baking supply stores such as N.Y. Cake, in recipes calling for gelatin. A kosher gelatin made of vegetable gum, tapioca dextrin, and acids is produced by KoJel.