January 16 2011

let’s stay together

Being home for the holidays means getting to spend quality time with my family. More specifically, it means that I get to hang out with my little brother, a fellow biochemist and food enthusiast. And being around my brother means getting to eat all of the crazy delicious confections he whips up during the wee hours of the morning (yes, marshmallows were actually made at 3 am). They may not be the prettiest sweets you’ll ever see, but they more than make up for it in taste. My current favorites are a homemade homage to the See’s Scotchmallow.

image

Being in the kitchen with my brother also means learning all kinds of science-y food facts. For example, did you know that the weird white coating that sometimes shows up on chocolate has a name? It’s called chocolate bloom. And it doesn’t end there. It turns out that there are even two different types of chocolate bloom — fat bloom and sugar bloom. Sadly, some of my brother’s chocolate succumbed to bloom while he was making candy. Poor chocolate…

image

A typical chocolate bar is a mixture of cocoa butter, cocoa solids, sugar, and an emulsifier such as lecithin. The cocoa butter and cocoa solids are made up of hydrophobic molecules (from the Greek for “water fearing”) while sugar is generally hydrophilic (also Greek, meaning “water loving”). Hydrophilic and hydrophobic molecules don’t mix well, so an emulsifier is used to help blend the different molecules and keep them from separating over time.

If you’ve ever made salad dressing, you probably know that it’s really hard to mix oil and vinegar. No matter how hard you shake, the oil and vinegar will ultimately separate because the hydrophobic oil molecules and hydrophilic vinegar molecules don’t like to be together. Yet adding just a bit of an emulsifier like mustard or egg yolk can make a huge difference. Why? Because these emulsifiers are made up of molecules that have both hydrophilic and hydrophobic components which help hold together hydrophilic and hydrophobic molecules (such and oil and vinegar) that otherwise wouldn’t mix well.

This basic idea of mixing hydrophilic and hydrophobic molecules also explains the driving forces behind chocolate bloom. Sugar bloom occurs when chocolate comes in contact with water. Because sugar mixes with water more readily than the fats in chocolate, any moisture that comes in contact with chocolate dissolves the sugar at the chocolate’s surface. As the water evaporates, a grainy white mess of sugar crystals is left behind.

Similarly, fat bloom occurs when hydrophobic cocoa butter molecules separate from the rest of the chocolate and make their way to the chocolate’s surface. The specific causes of fat bloom are a bit more complicated and have been the focus of several scientific studies. Who knew so much research went into something as simple as a chocolate bar?

About

Grad student by day, culinary enthusiast by night. What better way to combine my interests in science and cooking than to write about them here?

Do you have comments, questions, or ideas for future posts? Send them to bitesizedbiology(at)gmail(dot)com.

Tumblr users can contact me here.

And if you still don't have enough food science in your life, now you can even follow Bite-Sized Biology on Twitter!