In this podcast episode of Food Non-Fiction, we talk about the baker's dozen. When someone says "a baker's dozen" they mean 13. But why is it 13 when a dozen is actually 12? The history of "a baker's dozen" goes back to medieval England. In 1266, King Henry III revived an old statute called the "Assize of Bread and Ale", which set the price of bread in relation to the price of wheat. To make sure that even the poorest of citizens could buy bread (because it was a staple food), bread was priced at a quarter penny, a half penny or a penny. In years when wheat prices went up, the loaves got smaller, but you could still always buy bread for a quarter penny. The Worshipful Company of Bakers was the name of the baker's guild - one of the oldest guild in England. They were given the power to enforce the Assize of Bread and Ale and would punish bakers that sold underweight bread. In order to make sure they wouldn't be punished for selling underweight bread, bakers gave customers extra bread. Extra slices were called "inbreads" and extra loaves were called "vantage loaves".
References:
The Worshipful Company of Bakers
Phrase Origins
Bakers in the Middle Ages
Wonderopolis