ELI5: What is fermentation?

Context: Science 3 views Apr 1, 2026 2 min read

Fermentation is when tiny living things like bacteria or yeast break down sugars to make energy, and they also make other things like acid or gas.

Imagine you have a bunch of LEGO bricks (those are the sugars). Fermentation is like having little LEGO-eating monsters (bacteria or yeast) come along.

  • These monsters are hungry and need energy.
  • They eat the LEGOs and use the pieces to make energy so they can play and grow.
  • But they also make other things while they're eating, like maybe little LEGO cars (acid) or LEGO balloons (gas).
So, fermentation is a process where little creatures eat sugars and make energy, but also create other stuff as a byproduct.

Here are some examples:

  • Making yogurt: Bacteria eat the sugar in milk (lactose) and make acid, which makes the milk thick and sour, turning it into yogurt.
  • Making bread: Yeast eats the sugar in the dough and makes gas, which makes the bread rise and become fluffy.
  • Making beer or wine: Yeast eats the sugar in grapes or grains and makes alcohol, which is what makes these drinks alcoholic.
Basically, fermentation is like a tiny creature's way of eating and making energy, but it also leaves behind some interesting "presents" that we can use to make yummy foods and drinks.

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