Scientists Say: Colloid

Milk, fog and jelly have more in common than you think.

Jam is a type of colloid. Small particles of sweet fruit are suspended in water and pectin, which creates a sweet sticky treat.

PatríciaR/Wikimedia Commons

Colloid (noun, “KAHL-oyd”)

A colloid is any material in which tiny particles of one substance are spread through a larger volume of another substance. The tiny particles do not dissolve. Colloids come in many forms. Fog is a colloid in which drops of liquid water are spread through the air. Milk is a colloid, in which globs of fat stay suspended in watery fluid. Even jelly is a colloid, in which bits of sweetened fruit sit suspended in water and a thickener called pectin.

In a sentence

When people try to make tasty gluten-free baked goods, they sometimes add colloids to them to make them springy.

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Power Words

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colloid   A material in which tiny insoluble particles are spread throughout a larger volume of another substance. Colloids take many forms. Smoky air is a colloid. So is fog. Milk is a colloid, with tiny globs of butterfat suspended throughout the liquid. Whipped cream is a colloid too. Colloids typically don’t separate into their individual components over time. 

pectin  A water soluble substance that binds adjacent cell walls in plant tissue. Pectins also serve as a thickener in making jams and jellies.

suspension  A mixture in which particles are dispersed throughout the bulk of a fluid.

Bethany Brookshire was a longtime staff writer at Science News for Students. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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