Maths Says There's A Right And Wrong Way To Cut Christmas Cake

Cut your cake like this and that baby's gonna' be dry as a bone. Anna Pustynnikova/

Christmas dinner can be something of a ritual for those who celebrate during the festive season. Different households can hold very different ideas as to what absolutely must be present at the feast and how it should be prepared. Whether you’re a nut roast connoisseur or a firm defender of classic turkey, we all have our own favorites, and for some, a Christmas cake is the grand finale to a decadent day of dining.

If you consider yourself a master Christmas cake maker, you may be surprised to learn that – according to a scientific journal entry from 1906 – there is a right and wrong way to cut your cake. “What kind of nanny state is this?!” I hear you cry, but there is logic behind the 114-year-old theory.

Professor of Applied Mathematics at the University of Bath and Professor of Geometry at Gresham College Chris Budd recently hosted an online lecture titled “A Mathematical Christmas Stocking”, which touched on the subject. In the lecture, Budd explained why the traditional cake-cutting technique of slicing segments from the outside to the cake’s center is a poor approach, as it leaves more of the cake’s surface area exposed and therefore likely to dry out.

So, what’s the correct technique? Dusting off a rather old piece of research, Budd leaned on the 1906 journal entry by the polymath Sir Francis Galton entitled "Cutting a Round Cake on Scientific Principles,” published in Nature, to explain the answer.

“Christmas suggests cakes, and these the wish on my part to describe a method of cutting them that I have recently devised to my own amusement and satisfaction,” wrote Galton. “The problem to be solved was, “given a round tea-cake of some 5 inches across, and two persons of moderate appetite to eat it, in what way should it be cut so as to leave a minimum of exposed surface to become dry?”."


The above video demonstrates Galton’s solution, in which the cake is cut across the middle leaving two semicircles which, to use his own words, “are kept in apposition by a common elastic band that encloses the whole.”

The method ensures that the inside of what cake remains is at no point exposed to drying air, keeping your delicious Christmas cake moist (everyone’s favorite word) and delicious for as long as it hangs around. There are of course some limitations to this, in that no amount of mathematics and elastic bands can prevent the cake’s eventual decay.

Back in 2017, researchers found a remarkably well-preserved fruitcake that could well be the only survivor from Scott of the Antarctic's infamous 1910 expedition. "There was a very, very slight rancid butter smell to it, but other than that the cake looked and smelled edible! There is no doubt the extreme cold in Antarctica has assisted its preservation," said program manager for artifacts, Lizzie Meek, of the cake. However, it’s still not advisable you wait this long before eating yours.

So, does Bath’s Christmas mathematician practice what he preaches? “My daughter makes us a lovely Christmas Cake every year,” wrote Budd in an email to IFLScience. “Far too much to eat on Christmas Day. So, we always use the ‘Galton method’ to cut the cake. It works! I warmly recommend that everyone tries it. We also use a fair method to divide up the slices. However, as my son is also a mathematician, we generally disagree on whether my method is better than his.”

I suppose it’s more original than arguing over Monopoly.


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