Agar agar is a seaweed-derived powder that sets liquids into gels without gelatin, making it essential for plant-based cooking. Unlike gelatin which melts at body temperature for a melt-in-the-mouth quality, agar sets firmly at room temperature and holds its shape even in warm conditions. The critical technique is dissolving agar fully in water before heating — it must reach a full rolling boil and simmer for 1–2 minutes to activate its gelling power completely. Acid weakens agar's setting ability, so when making citrus gels, always add lemon juice or other acids after removing the pan from heat. This preserves both the gel's structure and the juice's bright, fresh flavor. If a gel sets too firmly, reduce the agar to three-quarters of the stated amount. If it fails to set, the agar was not boiled long enough or too much acid was added during cooking. A failed gel can be re-melted and reboiled to try again — unlike gelatin, agar tolerates reheating.