Bread rises because yeast produces carbon dioxide during fermentation. The gas becomes trapped in the dough’s gluten network, and oven heat expands the bubbles before the crumb sets.
Yeast makes gas
Yeast consumes available sugars and releases carbon dioxide and ethanol. The gas forms bubbles throughout the dough. Temperature, water, sugar and yeast activity control the rate, which is why dough can rise slowly in a cool room.
Fermentation also creates flavour compounds. Rising is not only a volume change; it is part of the dough’s chemistry.
Gluten holds the bubbles
Wheat proteins hydrate and link into an elastic gluten network. Kneading helps organise that network so it can stretch around gas cells rather than letting them escape immediately. Flour type and mixing change the strength of the structure.
A dough can contain gas and still fail to rise well if the network is weak or damaged.
The oven sets the crumb
Heat expands existing gas, creates steam and speeds reactions. Yeast eventually stops working, proteins coagulate and starch gelatinises, fixing the open crumb in place. Cooling allows moisture and structure to redistribute.
A loaf rises in stages: fermentation creates gas, gluten holds it and heat turns a flexible foam into bread.
Sources and evidence
- Washington State University — Why bread rises ↗
Yeast, gas bubbles and dough structure.
- USDA Agricultural Research Service — Bread science ↗
Ingredients, fermentation and baking transformations.
Sources consulted: 9 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Added original explanatory comparisons, source-linked evidence and a reader-focused example.