Demeter was the Greek goddess of bread and she was considered patron of bread. She was also the goddess of agriculture, milling, horticulture, pig farming, motherhood and of the blessed afterlife. See www.theoi.com/Summary/Demeter.html for details.
In ancient Roman mythology, a minor goddess, Fornax (the name means oven), was in charge of bread, yeast, the "mysteries of baking" and the oven doors - specifically, to make sure that people did not open the oven doors before the baking was finished. She had a feastival on the 17th of February called Fornacalia.