What It Is: Gelatin is made by boiling collagen-rich animal tissue in water to unravel the collagen into long protein strands. The gelatin is then extracted from the liquid and dried to create granules (powder).
How It Works: Achieving properly gelled gelatin is a two-step process. First, it must be bloomed, or hydrated, in cool water. The cool water penetrates slowly through each granule of gelatin, ensuring that it hydrates fully and dissolves. (If you skip blooming and add gelatin directly to hot water, the surface of each granule will rapidly hydrate and stick to its neighbors in clumps, while the interiors of the granules remain unhydrated and undissolved.)
The second step to properly gelled gelatin is heating, which causes the protein molecules to dissolve so that the mixture is fluid. Then, as the mixture cools to about body temperature, the strands tangle together, forming a mesh that slows the flow of the liquid, thickening it. Finally, after enough time has elapsed, that mesh is sturdy enough to stop the liquid from flowing altogether, turning it into a solid gel.