Agar by John Spottiswood.

Since gelatin is made from animal tissue, many vegetarians rely upon this seaweed derivative as a substitute. Like ordinary gelatin, agar is flavorless and becomes gelatinous when it's dissolved in water, heated, and then cooled. Agar, though, gels more firmly than gelatin, and it sets and melts at a higher temperature--it can even set at room temperature. Agar, like gelatin, is full of protein (though incomplete), but it also contains the rich array of minerals one would expect from seaweed. To use agar, just soak it in the liquid for about 15 minutes, bring it to a gentle boil, then simmer while stirring until it's completely dissolved. The liquid will gel as it cools. Acids weakens agar's gelling power, so if you're firming an acidic liquid, use more. Like gelatin, agar will break down if exposed to the enzymes of certain raw fruits, like kiwi fruit, papayas, pineapple, peaches, mangos, guavas, and figs. Cooking these fruits, though, destroys the enzymes. If you plan to add any of these fruits to a gelatin salad, it's a good idea to buy them in cans, since all canned fruit is pre-cooked. Agar comes in flakes, powder, or bars.