The strange physics of plant milks is just beginning to emerge

The physics of plant milks is strange. Scientists are just beginning to understand this and hope it could lead to better drinks.

Vivek Sharma at the University of Illinois Chicago and his colleagues found that most plant milks flow and drip in more complex and unusual ways than their animal counterparts.

The team examined eight different milks—cow, goat, pea, soy, oat, almond, coconut, and rice—and studied their viscosity, or how difficult it is for them to flow. They found that all plant-based milks except rice milk showed something called shear thinning, where viscosity decreases with pressure.

This means that these milks are non-Newtonian fluids, physically more similar to ketchup or shampoo, which flow more easily when pressure is applied to the bottle than cow’s or goat’s milk, which have a constant viscosity.

Sharma says this is because the plant-based milks contained very small amounts, often less than 0.1 percent, of gum derived from legumes or bacteria. These chews make them more stable and give them a creamier mouthfeel.

The non-Newtonian nature of these milks also affects how people interact with them every day, Sharma says. For example, drops of skimmed plant-based milk would spill more if spilled on a kitchen counter, while a cookie dipped in a glass of such milk would get a thinner coating.

The researchers believe that by studying the physics of the various properties of milk and the ingredients they contain, it should be possible to design new drinks with all the desired properties. Experienced food scientists may have remarkable empirical knowledge and intuition for processing milk, but they rarely work with rigorous physical models or measurements, Sharma says.

Sharma presented the work on 18 March at American Physical Society Global Physics Summit in Denver, Colorado.

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