Emulsifiers make it easier for the cook to prepare an emulsion, but they don’t necessarily result in a stable emulsion. Once formed, the droplets may be so crowded that they bump into each other or are forced up against each other, and the force of surface tension may pull them together and cause them to coalesce again. Fortunately, there are many kinds of molecules and particles that can help stabilize an emulsion once it’s formed. They all have in common the property of getting in the way, so that two approaching droplets encounter the stabilizers rather than each other. Large, bulky molecules like proteins do this well, as do starch, pectins, and gums, and particles of pulverized plant tissue. Ground white mustard seed is especially effective thanks both to its particles and to a gum that it releases when wetted. Tomato paste contains a considerable amount of protein (around 3%) as well as cell particles, and is a useful emulsifier and stabilizer.