Bread unpredictable since the steam is not produced until the bread is baked. Steam leavening happens regardless of the raising agents (baking soda, yeast, baking powder, sour dough, beaten egg white) included in the mix. The leavening agent either contains air bubbles or generates carbon dioxide. The heat vaporises the water from the inner surface of the bubbles within the dough. The steam expands and makes the bread rise. This is the main factor in the rising of bread once it has been put in the oven. CO generation, on its own, is too small to account for the rise. Heat
Bread and butter pudding can be used instead. Sometimes raspberry, strawberry, blackberry or mixed fruit jam, marmalade, or other sweet preserves will be spread upon the bread, along with the butter. Other modern variations include scattering fresh grapes between the layers of bread, melting apples into the egg-milk mixture, and using unusual types of breads — such as brioche — to make it. Lemon or orange peel will add a characteristic flavour. The earliest bread and butter puddings were called "whitepot" and used either bone marrow or butter. Whitepots could also be made using rice instead of bread, giving rise to the rice pudding