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Kitchen science · Fermentation and measurement

Yeast and sourdough: the living things that make dough rise

The holes in bread begin with yeast eating sugar and giving off carbon dioxide. Find out at what temperature yeast speeds up, where it dies, how the gluten network traps the gas, and where the sour taste of sourdough comes from.

  • 16 min
  • 2 simulations
  • Mini quiz

Updated:

Preview

The question

A bowl of dough was kneaded in the evening and covered. By morning it has doubled in size and its surface has risen into a dome. The bowl was covered; nothing got in. So who puffed the dough up?

And why does the same dough barely move in the fridge, yet overflow its bowl next to a radiator? Where exactly do the spongy holes in a loaf fresh from the oven come from?

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Matching

Who does what in the dough?

Choose a job for each player (radio buttons; the arrow keys work too). When you have matched them all, press Check.

Prediction

Predict first

Where do you think most of the sour taste of sourdough bread comes from?

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Ordering

From fridge to oven

Put the cards in order by dragging them or moving them with the keyboard, then press Check.

Prediction

Predict first

At what stage do you think the yeast in the dough dies?

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Frequently asked

5 questions

What makes dough rise?

Baker's yeast, Saccharomyces cerevisiae, a living single-celled fungus. The yeast turns sugar into ethanol and carbon dioxide by fermentation, and it is the carbon dioxide that raises the dough. The gluten network in wheat holds the gas in.

Will dough rise faster if I start the yeast in hotter water?

Only up to a point. Yeast works fastest at about 25–35 °C, struggles above 40 °C, and dies above about 50–60 °C, after which the dough will not rise at all. The water should be lukewarm: slightly warm on your wrist, but not hot.

Does the yeast die if I put dough in the fridge?

No. At about 4 °C yeast slows down a lot but does not die; the dough rises a little overnight. Take it out and leave it somewhere warm and it speeds up again. This cold fermentation often gives more flavour, too.

Does yeast make the holes in bread?

Yeast does not create new bubbles. It inflates the tiny air bubbles that got into the dough during kneading with the carbon dioxide it makes, and the gluten network holds them. This is one reason why well-kneaded dough has a finer, more even crumb.

Is sourdough a kind of yeast, and is it suitable for coeliac disease?

Sourdough is not a single organism but a community of wild yeasts and lactic acid bacteria; its sourness comes from the lactic and acetic acids the bacteria make. Sourdough wheat bread still contains gluten, so it is not suitable for people with coeliac disease.