Thickening Agents: Proteins

The simplest protein thickener is gelatin, which unwinds on heating into long molecular threads, tangling and impeding the movement of water molecules. However, at concentrations needed to produce noticeable thickening, the liquid will gel on cooling. Other proteins (blood, egg yolks, or liver) can also be used. Unlike gelatine, these proteins coagulate on heating, and form such strong bonds that they may squeeze out the trapped liquid, causing the sauce to separate out.

Dairy products like cheese and yoghurt are also used to thicken; however their proteins have already been coagulated—they act by lending their own thickness to the sauce.