As summer starts up so do campfires and toasted marshmallows. So what gives a golden brown, melty marshmallow its amazing flavour? What makes them puff up? And why isn’t a burnt one as sweet anymore?
Let’s start with the ingredients of a marshmallow. A marshmallow is around 50% air. This actually starts to answer our second question about why marshmallows expand when they heat up. The air expands as it warms up so the marshmallow gets bigger. But back to the ingredients. The rest of the marshmallow is gelatin, which doesn’t have much of a direct role in a perfectly toasted marshmallow, and sucrose. Sucrose is a type of sugar that has two other sugars inside of it. Sucrose is basically a glucose and a fructose stuck together. All sugars are made of carbon, hydrogen, and oxygen in related but different amounts. This is important because as it burns it releases carbon dioxide and water vapour. This is the second reason the marshmallow expands is there is actually more gas.
So now, how does it get so tasty? As the sugar heats up some of the chemical bonds start to break. Sucrose starts to break down into its components: the glucose and fructose. In the process, volatile chemicals are released. Volatile chemical just means that they are very likely to turn from solid or liquid into vapour. The different chemicals have slightly different flavours and odours. This starts to happen when sucrose reaches 160°C (320°F). This is easier to do over warm coals that directly over the flame due to the consistency of the heat. So now we have our warm, toasty flavour.
Our last question is why we don’t get more toasty flavour from a burnt marshmallow? Remember that sucrose broke down at 160°C into glucose, which also breaks down at 160°C and fructose, which breaks down at 110°C. This means that you can get too much of a good thing. The base sugars will start to break down until there is no sugar left. At that point you’re left with carbon on a stick.
So the next time you’re hanging out, toasting marshmallows, think about all the chemistry that goes into that tasty ball of goodness.