The most important influence on the texture of a jelly is the concentration and quality of its gelatin. Gelatin is a highly variable material. Even manufactured gelatin (below) is only 60–70% intact, full-length gelatin molecules; the remainder consists of smaller pieces that are less efficient thickeners. The gelatin in a stock is especially unpredictable, since meat and bones vary in their collagen content, and long cooking causes progressive breakdown of the gelatin chains. The best way to assess gel strength is to cool a spoonful of the liquid in a bowl resting in ice water, see if the liquid sets, and how firm the gel is. A liquid lacking in firmness can be reduced further to concentrate the gelatin, or it can be supplemented with a small amount of pure gelatin.