Dear Straight Dope:
I can't find anything on why a baker's dozen is 13. I heard that it came from the time when royalty had food testers. Thus, the tester got one and the dozen was still intact for the king or queen. For some reason I don't buy that. Help.
SDStaff Dex replies:
I don’t buy it either. I’ve got a much simpler theory, and if you don’t like it I’ve got a slightly more complicated one that doesn’t require us to drag in the royalty.
The first theory goes back to ancient times. Bakers were widely viewed with suspicion, since it was common (and easy) for them to short-weight customers. Many societies had severe penalties for bakers who engaged in such underhanded practices. For instance, one source says that in ancient Egypt, the baker’s ear was nailed to the doorpost of his bakery if he were found selling light loaves. (I’m not sure whether the ear was still attached to the baker. Either way it was a pretty stiff punishment.)
Under the code of Hammurabi, a loaf of bread and a man’s hand were interchangeable. They took their bread seriously back then.
In the mid-13th century, British law imposed strict regulations on bakers regarding the weight of bread. Bakers wanted to make sure they complied, since the penalties were severe (a fine or the pillory, although nothing involving ears, so far as I know). It was difficult to make loaves of uniform weight in those days before automation, so bakers added a 13th loaf to every shipment of 12–better to be overweight than under. Thus “a baker’s dozen” meant 13.
The second theory is more complicated. A baker selling to a third party (a street vendor, say) would add a 13th loaf as the profit for the middleman. That is, the baker sells the middleman 13 loaves for the price of 12, and the middle man sells the 13 individual loaves for a 7.7% profit.
Whichever theory you accept, the evolution of the expression today has come to mean that the baker adds an extra cookie, bun, pastry or whatever to the order of 12 as a bonus.
By the way, the word “baker” itself, meaning one who bakes (duh), dates from around the year 1000. A variant is bakester, which survives in the surname Baxter. As Cecil has pointed out, some think -ster is a female ending and that a bakester or baxter was originally a female baker, just as there were websters (female weavers) and spinsters (female thread spinners). But those acquainted with many gangsters, mobsters, or teamsters (not saying these three terms are in any way related) may have their doubts.
SDStaff Dex, Straight Dope Science Advisory Board
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