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A fungus breathing out

Why Does Bread Rise?

Yeast is a living fungus that eats sugar and releases gas, which inflates the dough.

1 Yeast eatssugar in thedough2 It releasescarbon dioxide3 Gas is trappedand the doughrises
A microbe, doing all the work.

  1. Step 1 of 5

    Yeast is alive.

    Dried yeast Dormant, waitingWarm water and sugar Alive and feeding

    It is a single-celled fungus. Dried yeast is dormant, and warm water and food wake it up within minutes.

  2. Step 2 of 5

    It eats sugar and gives off gas.

    Sugar in the dough Carbon dioxidereleased

    Flour contains starch that breaks down into sugar. Yeast consumes it and releases carbon dioxide and alcohol as waste.

  3. Step 3 of 5

    Gluten traps the bubbles.

    Unkneaded Gas escapes — flatKneaded Stretchy network trapsit — rises

    Kneading builds a stretchy protein network that holds gas in. Without it — as in a cake without raising agents — the gas simply escapes.

  4. Step 4 of 5

    Warmth controls the speed.

    Warm placerises in an hourRoom temperaturea few hoursFridgeovernight

    Yeast works fastest around 25 to 30°C. Cold slows it right down, which is why slow overnight rises happen in the fridge.

  5. Step 5 of 5

    The oven finishes the job.

    1 Heat expandsthe gas2 One last rise3 Structure sets— bubbleslocked in

    Heat makes trapped gas expand sharply for a final rise, then kills the yeast and sets the structure. The bubbles are locked in permanently.

    The alcohol yeast produces bakes off almost entirely. The same organism makes both bread and beer.

The short version

Yeast eats sugar and releases carbon dioxide, and a stretchy gluten network traps the gas so bread rises.

Try it yourself

Mix yeast, warm water and sugar in a bottle and stretch a balloon over the neck. It inflates within the hour.

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