Yeast!
The ingredient in bread that produces carbon dioxide is yeast.
yeast.
Yeast produces carbon dioxide when they eat which makes those tiny wholes in bread. As yeast produces the carbon dioxide the bread expands and with all the ingredients in the dough of the bread it creates the bread we eat.
carbon dioxide
Carbon dioxide
carbon dioxide
When glucose is added to yeast in solution, the enzymes inside it turn the mixture into ethanol and carbon dioxide, so, for your question, carbon dioxide. It also respires normally (aerobically) and then too produces carbon dioxide.
Carbon dioxide
Yeast produces CO2 gas and sometimes ethenol when it metabolizes sugar.
In yeasts, fermentation results in the production of ethanol and carbon dioxide – which can be used in food processing: Bread – Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking.
Yeast is a living organism (a fungus). It feeds off the sugar in the bread and respires, meaning that it takes in oxygen and gives out carbon dioxide. The carbon dioxide given out forms bubbles in the thick dough and these become the air spaces found in the bread after it is baked.
Bread gets big holes through the fermentation process. This process produces bubbles of carbon dioxide within the grain of the bread, thus causing holes.