What causes the glossy skin on top of brownies? Some kitchen science tries to figure that out

Brownies have a glossy top surface. What exactly is up with that? Why … glossy?

Adam Ragusea wondered, so he dialed up Pia Sörensen, a Harvard professor who teaches a course called "The Science of Cooking" — and with her expertise to guide him, did some superb kitchen science to figure out what's going on.

There are, as Ragusea notes in the video he shot about his research, three major hypotheses about what causes the top layer of brownies to be glossy.

Number one, the cocoa butter hypothesis — people who say you get a shiny crust if you use lots of solid chocolate containing cocoa fat in your batter.

There is the sugar dissolution hypothesis — people who say it's all about whether you sugar is fully dissolved into the aqueous phase of the batter.

And then there's the meringue hypothesis. Lots of people say the trick to getting that skin is to beat the batter really thoroughly, or even to beat the eggs and sugar alone to create an egg foam.

So Ragusea bought some lab equipment, baked a ton of brownies, scraped off their top glossy layer, and began analyzing it.

I won't spoil what he and Sörensen figured out — which of the three hypotheses is correct — so you'll have to watch the video to see. But the journey here is just as excellent as the destination.