A gel is a soft solid built from a network that traps liquid: pectin, gelatin, starch or alginate chains linked into a three-dimensional mesh holding water or juice. The network sets texture, from the wobble of a dessert jelly to the firmness of processed fruit and vegetable products. Calcium ions cross-link alginate and low-methoxyl pectin into firm gels, which is why calcium chloride firms pickles and canned tomatoes. Gel strength, syneresis and melting behaviour are the quality measures, tuned by hydrocolloid choice, sugar, acid and temperature.