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 circuses range of different themes including lust for power and desire for old age to illustrate his argument. Roman politicians passed laws in 140 B.C. to keep the votes of poorer citizens, by introducing a grain dole: giving out cheap food and entertainment, "bread and circuses", became the most effective way to rise to power. Juvenal here makes reference to the Roman practice of providing free wheat to Roman citizens as well as costly circus games and other forms of entertainment as a means of gaining political power. The "Annona" (grain dole) was begun under the instigation of the "popularis" politician