Cookie Dunking – For SCIENCE!!

In the latest issue of WIRED, they tackle that every day problem of the best way to dunk cookies into milk, a problem which, let’s face it, has enamored the geekiest amongst us from time to time. What is the optimal time for a cookie to be in milk before falling apart in a goopy mess into the milk cup?

Their findings? The Washburn equation that could be used to optimize cookie-dunking. The equation looks like this:


t is the time for a liquid of dynamic viscosity η and surface tension γ to penetrate a distance L into the capillary whose pore diameter is D.

All of this is a fancy way of saying every porous material out there has a set amount of liquid it can hold. If you push it beyond that limit? You get goop.

So how much time should a cookie be in milk before it hits that stage? Len Fisher, a visiting fellow in physics at the University of Bristol, England, determined in 1998 that somewhere between 3.5 seconds to 5 seconds is the optimal time (depending on what kind of cookie, which ingredients were used, etc, etc.)

But, Fisher found, this is if you dunk cookies the traditional way, that is to say, vertically into the milk. If you decided to dunk your cookies horizontally, and only place half of the cookie into the milk, you could keep it in between 14 and 20 seconds.

So now you know.