Baker's Dozen 13

Baker's Dozen 13, A baker's dozen, devil's dozen, long dozen, or long measure is 13, one more than a standard dozen. The oldest known source, but questionable explanation for the expression "baker's dozen" dates to the 13th century in one of the earliest English statutes, instituted during the reign of Henry III (1216–1272), called the Assize of Bread and Ale. Bakers who were found to have shortchanged customers (some variations say that they would sell hollow bread) could be subject to severe punishment. To guard against the punishment of losing a hand to an axe, a baker would give 13 for the price of 12, to be certain of not being known as a cheat. Specifically, the practice of baking 13 items for an intended dozen was insurance against "short measure", on the basis that one of the 13 could be lost, eaten, burnt, or ruined in some way, leaving the baker with the original legal dozen. The practice can be seen in the guild codes of the Worshipful Company of Bakers in London.


However, there is some doubt over whether this is the real explanation for the expression, because baking 13 instead of 12 units has been good practice all over Europe, not only in England. It also seems unusual that only bakers deliver 13 in a dozen, and not, for example, butchers. An alternative explanation for why specifically bakers deliver 13 in a dozen has been found in the tidy way 13 disks (loaves, cookies, biscuits, etc.) can pack a rectangle (baking tray) of appropriate proportions. Packing trays have a 3:2 aspect ratio, and the most efficient two-dimensional array is hexagonal close packing, which has sixfold symmetry, such that each baked item is equidistant from its six nearest neighbours. The corners of a cookie sheet heat up and cool off faster than the edges and interior, so any item placed near a corner will not bake at the same rate as the other items. A 4+5+4 arrangement provides the dense hexagonal packing while avoiding corners, and would have been discovered empirically by bakers with the goal of baking the maximum number per batch with optimal uniformity.

According to the 1811 Dictionary of the Vulgar Tongue, by Capatin Grose, a Baker's Dozen is "Fourteen; that number of rolls being allowed to the purchaser of a dozen".

Source:http://en.wikipedia.org/wiki/Baker%27s_dozen#Baking