Happy National Donut Day! While we can agree that all donuts are delicious, not all donuts are made equally. The perfect donut, many would argue, is fried to a golden crisp on the outside and is soft and chewy on the inside. Purists would insist on only a dusting of sugar. But between the deep-fried goods peddled by Dunkin Donuts, Krispy Kreme, and countless independent donut artisans, it’s easy to be overwhelmed by choice. How do we make sure we get the perfect donut every time?
Science, as always, has the answer.
The ultimate ring donut, according to Eugenia Cheng, Ph.D., a mathematician at Sheffield University, has to optimize both its crispy surface area and the volume of its “squidgy” insides. Figuring out a mathematical formula for the perfect donut was made easier by the fact that a donut is pretty much a torus, which Cheng says is an “important mathematical object, as well as being delicious.”
A disproportionately big donut hole would create too much surface area, so the pastry’s crispiness might overpower its softness; but make the donut hole too small, and it’ll take a lot more to perfect its crust.
Using calculus, Cheng determined that the optimal donut hole size should be 0.4 inches, and its diameter should be somewhere between 2.8 and 3.2 inches.
That leaves us with a donut with 78 percent squidge and 22 percent crisp — a mathematically perfect pastry.