Blooming cocoa powder
You see it all the time in recipes for brownies, chocolate cakes, and pretty much anything else with cocoa powder: the instruction to pour boiling water (or sometimes coffee, or even red wine) over the cocoa powder to “bloom” it. As I dutifully heat my liquid, I always wonder what difference this extra step makes and if it’s really worth it. In BakeWise, Shirley Corriher writes that blooming cocoa powder gives it a richer, fuller flavor and also helps it dissolve more easily. But much as I like Shirley Corriher, I needed to see this one for myself.
I prepared two bowls with one tablespoon each of cocoa powder, then added the water: one got a quarter cup of boiling water and the other a quarter cup of cold tap water. I stirred it all together and noticed a difference immediately. The cocoa powder dissolved readily in the hot water but resisted my best efforts in the cold water–even a full minute of vigorous whisking left grainy lumps. I stirred in a teaspoon of sugar to make them easier to taste and let the hot bowl cool to room temperature.
It only took a sip to know that Shirley Corriher was right on both points. The hot water brought out more flavors in the chocolate, creating a strong, full-bodied drink with deep flavor and hints of coffee. The cocoa powder dissolved fully and left a smooth texture. In contrast, the cold water never fully dissolved the cocoa powder and created a gritty drink without the dark, rich flavor of good chocolate. It seemed more acidic and only carried the thin high notes of flavor, without the bass line to support it.
So my experiment left no doubt that I should take the time to bloom my cocoa powder, but I’m still not fully satisfied with the explanation for why. I can’t find much in the way of sources for this, but I think the presence of residual cocoa butter in cocoa powder plays a big role here. With powders containing up to 30% cocoa butter, they need the hot water to melt the fat in order to dissolve smoothly. Dissolving easily in turn allows more volatile compounds from the powder into the water, which makes it more flavorful. It’s also possible that the heat may break some larger molecules into smaller, more flavorful pieces.
Whatever the mechanism (and if you have more insight, please tell me!), taking a minute to heat some water and bloom your cocoa powder makes a big difference in both flavor and texture. Need to prove it to yourself? Go make a big mug of hot chocolate–in the name of science, of course.