Oreo Dunking Physics

As most people know, cookie dunking is serious business. Everyone has their own preference for cookie saturation and stiffness. Happily, scientists have examined this problem and have advice to offer those seeking cookie dunk perfection. Previously, we discussed Len Fisher’s Ig Nobel Prize-winning work on the physics of cookie dunking. In that work, Fisher found that Washburn’s equation for flow through cylindrical pores worked well to describe the uptake of tea or milk into a cookie.

More recently, Splash Lab researchers have investigated just how much milk several common American cookies – including Oreos – take up in a given dunk. Because these cookies are quite dry, they take up liquid quickly, soaking in about 80 percent of the liquid weight within the first 2 seconds when dipped in 2% milk. Within five seconds, the cookies take on 99% of their liquid weight capacity, so there’s no point to a longer dunk – unless you like your cookie to disintegrate into the milk. The fat and sugar content of the dunking liquid does affect how quickly capillary action can whisk fluid into the cookie’s pores, but, overall, the research shows that milk users should be well-served by a three second dunk. If you like your cookie softer than that, simply pull it out of milk and let it sit for a bit while the milk soaks in. That way, your cookie doesn’t crumble! (Image credits: A. Melton; research credit: R. Hurd et al.; h/t to Randy H. and Mental Floss)

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