Always choose a chocolate dip

How to Dunk a Doughnut
March 14, 2003

If Len Fisher invites you to dinner, cancel everything to be there. No superchef has thought more closely about food and its enjoyment than Fisher, a physicist from Bristol University.

Fisher shows how science works with reference to the everyday.

He sprang to fame in 1999 when he won an Ig Nobel prize in physics for his research on biscuit dunking, the successor to his groundbreaking work on doughnut immersion. Doughnuts are ideal for dunking because they are a 3D web of gluten with many channels for the liquid to penetrate. This research led to an industry-sponsored follow-up on biscuits, where the science is trickier. An estimated one in five biscuit dunks ends in disaster. This is because biscuits contain sugar and fat, both of which dissolve, and starch, which absorbs liquid until the weakened structure collapses. The trick is to dunk the biscuit sideways, ideally with an impermeable layer to add waterproof strength. The next time you are choosing between plain and chocolate biscuits, remember that science demands chocolate.

Dunking may seem trivial, but Fisher's research did its sponsors proud, bringing in 7,000 calls in 15 minutes to an Australian radio station and featuring on US television. It also touches on capillary force and random-walk theory, and sheds light on serious issues, including ship sinkings and blood flow. Fisher did tangible work on the project, including using a sander to make ever-thinner biscuits, which left him covered in both crumbs and the derision of his colleagues.

He also addresses the more serious topic of how food cooks. He has taken part in cooks-meet-scientists conferences at which thermocouples were sunk into meat during cooking to show how heating progresses. Because heat takes time to get from the outside of the joint to the centre, the temperature at the core keeps on rising after the meat is taken out of the oven, which is why it is important to let meat stand before carving it.

Turning to the world of DIY, Fisher stays on good form. He looks at tools from chisels to wheelbarrows and finds that most are one or another type of lever. Pulling out a nail with a claw hammer gets harder as the nail emerges because the point at which the hammer pivots on the hard surface gets closer to the nail.

Less useful is Fisher's method of guessing supermarket bills; his statistical analysis produces a method that is too cumbersome. And you may feel less than fulfilled by his analysis of the physics of sex, which concentrates on such matters as how sperm swim, revealing that what they do is nearer to rowing. Better is his explanation of how to arrive at the right time and place to catch a ball (keeping it in the same position in your field of view as it flies and you run is key).

For maximum satisfaction, stick with the work on food. Fisher's study of gravy absorption, in which ciabatta comes out top for absorbency, is the sort of enjoyable survey that makes science indisputably accessible.

Martin Ince is contributing editor, The THES .

How to Dunk a Doughnut: The Science of Everyday Life

Author - Len Fisher
ISBN - 0 297 60756 1
Publisher - Weidenfeld and Nicolson
Price - £12.99
Pages - 241

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