Friday fun fact #7: A baker's dozen

(Photo taken from Google Images)

Did you know that a baker's dozen is, in fact, 13 and not 12? Well, maybe you did. But, do you know why?

The expression goes back to the times of Henry II of England (1154 - 89) but the origen of the expression goes much further back in time, probably to the year 1000.

As it is very difficult to calculate the exact quantity of dough needed to make a loaf, bakers were often finding that they were accidentally cheating their customers. If they were found out that they had sold short then they were quite likely to have their hand chopped off! Not good. This was also true in other countries, like Egypt and Babylon where similar fates awaited those who were accused of selling 'light loaves'.

So, to get around the problem, the bakers started to add a loaf of bread to their vendor's or customer's sack, giving them 13 loaves for every 12 ordered. The addition was called the 'in-bread' or 'vantage loaf'.

This practice eventually made its way into the Worshipful Company of Bakers (London) guild code.  This guild was actually started in the 12th century and had a large part in formulating the rules on the Assize of Bread and Ale statute.

While modern bakers no longer fear medieval law, they have found other reasons for a baker's dozen, as seen in the tidy way 13 disks (loaves, cookies, biscuits, etc.) can pack a rectangle (baking tray) of appropriate proportions. Modern standard sized 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. 

Talking of cookies, I'm off to bake some for the weekend. It rained ALL DAY yesterday so you can guess which ones I'll be baking. See here if you are in any doubt!