Q.Why does bread dough rise before baking? Identify the microorganism involved and describe the biochemical process responsible for the rise.

[!TLDR] The yeast Saccharomyces cerevisiae ferments sugar in the dough, releasing CO2 that gets trapped and makes the dough rise.

[!ANSWER] Saccharomyces cerevisiae (baker's yeast) ferments sugars in the dough, releasing carbon dioxide gas that is trapped by the dough's elastic gluten network, causing the dough to rise before baking.

Bread dough rises because of the metabolic activity of the yeast Saccharomyces cerevisiae, mixed into the dough along with sugar. As the yeast ferments the available sugars, it releases carbon dioxide gas and a small amount of ethanol as by-products. The dough is elastic, thanks to a protein network called gluten, so the carbon dioxide produced gets trapped inside as countless tiny bubbles rather than escaping freely. This trapped gas causes the dough to expand, or 'prove', before it is baked. During baking, heat further expands these bubbles before setting the structure permanently, producing bread's light, porous, spongy texture; the small quantity of ethanol produced simply evaporates away during baking.

[!ANSWER] The yeast Saccharomyces cerevisiae ferments sugar in the dough, releasing CO2 gas that is trapped by the dough's gluten network, causing it to rise before baking.

Name the organism, then explain the mechanism as a two-part chain: fermentation produces gas → the dough's elastic structure traps the gas as bubbles, which is what physically causes the rise.

A common error is saying yeast 'produces air' rather than specifically carbon dioxide gas from sugar fermentation, or forgetting to explain why the gas doesn't simply escape (the gluten network trapping it).