Leavening is the action used to introduce bubbles into dough which when cooked, leaves a matrix of holes, often supported by proteins such as gluten that make the product airy and light.
There are many ways used to leaven doughs:
- Biological leaveners
- Chemical leaveners
- Mechanical leaveners
- Beating or whisking (particularly with egg-whites)
- Creaming - mixing sugar crystals and solid fat
- Introducing crushed ice and quickly cooking so the ice melts, leaving air-gaps
Unleavened, particularly when applied to bread, is when no leavening or rising agent is used. This normally means no yeast is used, due to religious taboo.