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
Cockle bread in which the bread is mentioned: Writing in "Observations on the Popular Antiquities of Great Britain" in 1854, John Brand describes the nursery rhyme as "modern", but adds that its connection to the earlier "moulding" of cockle bread "is by no means generally understood". Cockle bread Cockle bread was an inferior type of British corn or wheat bread mixed with "cockle weed". In the 17th century a practice known as "moulding" cockle-bread had a sexual connotation. Cockle bread is also mentioned in a 19th-century nursery rhyme. The play "The Old Wives' Tale" by George Peele, first published in 1595, has