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What is Viscosity?
Viscosity is the "resistance to flow" that a liquid has. At its most basic this just measures how easy something is to pour. Water has a low viscosity and maple syrup, especially cold out of the refrigerator, has a high viscosity.
Taken from the Latin word viscum, viscosity is an inner characteristic of fluids which refer to its measure of resistance to flow. Fluids which are thinner have lower viscosity. Likewise, liquids which have higher viscosity are thicker. Greater movement comes with fluids which are less viscous. This property is also known as fluidity.
This opposition to flow can be broken by shear stress. When viscosity is referred to exclusively for liquids, it is defined as internal friction or thickness.
Aside from sheer stress, other factors may affect viscosity as well. Temperature is one of the biggest factors. Viscosity can differ according to the amount of heat that it is exposed to.
Most simple fluids have a tendency to flow more freely when exposed to higher temperatures. Conversely, lower temperatures will decrease the ability of simple fluids to flow.
Pressure may also affect viscosity when presented in great amounts. Liquids which are exposed to large amounts of pressure may become more viscous due to the compression of molecules.
Many classic and modern cuisine techniques consider viscosity in the creation of dishes. The thickness or thinness of liquids in a dish plays a role in presentation, texture, as well as flavor of a dish.