Cloudy Suspensions: Thickening with Particles

Most of our raw ingredients— vegetables, fruits, herbs, meats—are plant or animal tissues built from microscopic cells that are filled with watery fluids. The cells are contained within walls, membranes, or thin sheets of connective tissue. (Dry seeds and spices contain no juices, but are still made up of solid cells and cell walls.) When any of these foods is broken apart into small pieces by being ground in a mortar or pulverized in a blender, they are turned inside out, so the fluids form a continuous phase that contains fragments of the solid cell walls and connective tissue. These fragments obstruct and bind the water molecules, and thus thicken the consistency of the mixture. Such a mixture of a fluid and solid particles is called a suspension: the particles are suspended in the fluid. Sauces made from pureed foods are suspensions.