The Science of Dunking

Can science do anything to bring the dedicated biscuit dunker into parity with the dunker of doughnuts? Could science, which has added that extra edge to the achievement of athlete and astronaut alike, be used to enhance ultimate biscuit dunking performance?

Doughnuts might have been designed for dunking. A doughnut, like bread, is held together by an elastic net of the protein gluten. The gluten might stretch, and eventually even break, when the doughnut is dunked in hot coffee, but it doesn’t swell or dissolve as the liquid is drawn into the network of holes and channels that the gluten supports. This means that the doughnut dunker can take his or her time, pausing only to let the excess liquid drain back into the cup before raising the doughnut to the waiting mouth. The only problem that a doughnut dunker faces is the selection of the doughnut.

Biscuit dunkers face much more of a challenge. If recent market research is to be believed, one biscuit dunk in every five ends in disaster, with the dunker fishing around in the bottom of the cup for the soggy remains. The problem for serious biscuit dunkers is that hot tea or coffee dissolves the sugar, melts the fat and swells and softens the starch grains in the biscuit. The wetted biscuit eventually collapses under its own weight.

Can science do anything to bring the dedicated biscuit dunker into parity with the dunker of doughnuts? Could science, which has added that extra edge to the achievement of athlete and astronaut alike, be used to enhance ultimate biscuit dunking performance and save that fifth, vital dunk?

These questions were put to me by an advertising company wanting to promote ‘National Biscuit-Dunking Week’. As someone who uses the science underlying commonplace objects and activities to make science more publicly accessible, I was happy to give ‘The Physics of Biscuit Dunking’ a try.

The first question that we asked was ‘What does a biscuit look like from a physicist’s point of view?’ We decided to be reductionist about biscuits, attempting to understand their response to dunking in simple physical terms and leaving the complications until later. When we examined a biscuit under a microscope, it appeared to consist of a tortuous set of interconnected holes, cavities and channels (so does a doughnut). In the case of a biscuit, the channels are there because it consists of dried-up starch granules imperfectly glued together with sugar and fat. To a scientist, the biscuit dunking problem is to work out how hot tea or coffee gets into these channels and what happens when it does.

One of the tasty heroes of our story

With this picture of dunking in mind, I sat down with some of my colleagues in the Bristol University Physics Department and proceeded to examine the question experimentally. Solemnly, we dipped our biscuits into our drinks, timing exactly how long they took to collapse. This was Baconian science, named after Sir Francis Bacon, the Elizabethan courtier who declared that science was simply a matter of collecting a sufficient number of facts to make a pattern.