Learn the science behind:
Gently press into a marshmallow. And let it go.
It should have bounced right back up
Now, drop one in a glass of chocolate milk. Does it float or sink?
Marshmallows are light and airy, while being bouncy to the touch, thanks to great teamwork of two, maybe three ingredients: sugars, gelatin, and possibly egg whites. Let’s see how this small but mighty team creates a marshmallow.
- Air bubbles make marshmallows light and fluffy
- Sugars contribute sweetness and firmness
- Sugar is added as a hot syrup
- Egg whites enable air bubbles
- Gelatin keeps it stable over time
- A tip for cleaning up
- Listen to our marshmallow podcast episode!
Air bubbles make marshmallows light and fluffy
Marshmallows are a very light style of candy. They float on top of hot chocolate milk and even a handful doesn’t seem to weigh anything. That’s because marshmallows are a foam. They contain a lot of tiny air bubbles which are surrounded and stabilized by sugar and proteins from egg whites and gelatin. Since air doesn’t weigh much, adding it into a product decreases its density. That is, the same volume of that product will weigh less.
A bouncy foam
Marshmallows aren’t the only food foams out there. Ice cream, foam on top of a beer, chocolate mousse, these are all foams as well. What sets marshmallows apart though is their bounce. You can compress them. But, they’ll bounce back upon release. Try doing that to ice cream or chocolate mousse, and you’ll simply see a fingerprint left behind.
It’s the delicate interplay of a marshmallow’s three core ingredients that makes this possible: sugars + gelatin + egg whites. Let’s have a look at each and how they impact the texture of marshmallows.
Sugars contribute sweetness and firmness
Look at the label of a pack of marshmallows, or a marshmallow recipe – we have one at the bottom of this post. Most likely, the main ingredient is sugar. Of course, sugar makes marshmallows sweet. But that’s not all, a marshmallow wouldn’t be able to hold its shape without the sugar!
As a thought experiment, remove the sugar from the marshmallow recipe below. You’ll be left with just 2 egg whites and a few grams of gelatin. You can’t make anything that resembles a marshmallow from just those ingredients. What’s more, removing the sugar will make it virtually impossible to make a nice brown marshmallow during roasting.
Marshmallows contain various types of sugar
Most marshmallows don’t contain just one type of sugar. Often, they’ll contain regular sugar as well as corn syrup – also referred to as glucose syrup. They each have a slightly different role:
- Regular sugar is made from sugarcane or sugar beet. It is made up of just sucrose molecules. It dissolves very well in water, but the slightest disturbance can cause it to crystallize. A sugar solution with a very high sugar concentration is very thick and viscous. This is ideal for making marshmallows.
- Corn syrup is made from corn and is a mixture of different sizes of sugars. It contains glucose and fructose, but also larger polysaccharides. Corn syrup helps prevent the crystallization of regular sugar. However, too much corn syrup can cause a marshmallow to become sticky.
Honey can add some extra flavor
For some recipes, you may be able to replace the corn syrup in marshmallows with honey. Honey is a mixture of different types of sugar, but it does have a different composition than corn syrup. It can help prevent the crystallization of sugar, but may also make a marshmallow stickier. Lastly, keep in mind that honey has quite a strong flavor. For some, this is an advantage, for others, not so much.
Sugar is added as a hot syrup
Regular sugar is grainy and made up of large crystals. Marshmallows on the other hand are very smooth and don’t contain any rougher particles. This is why sugar has to be dissolved in water first. By dissolving the sugar, the sugar crystals break down and the sugar syrup is fully liquid, not grainy.
The temperature of the syrup is crucial
Once the sugar is dissolved, you’ll have to cook the sugar syrup. By boiling a sugar syrup, you evaporate water. The hotter the sugar syrup, the more water you’ve evaporated.
By concentrating the sugar syrup it becomes more viscous. This helps ensure that your final marshmallow will be dense, stable, and firm.
The temperature of a hot boiling sugar syrup is a measure of its concentration. The higher the boiling point, the more concentrated it is. Recipes for marshmallows generally give an exact temperature to which a sugar syrup should be cooked. This ensures that the concentration of sugar is high enough.
The hot syrup cooks eggs and melts gelatin
Once that sugar syrup is hot enough, you’ll have to pour it in with the egg whites and gelatin. It needs to be poured in while it’s still hot. This way, it will:
- Cook egg whites: this helps the proteins in the egg to uncurl and stabilizes the marshmallow;
- Melt the gelatin: gelatin dissolves at higher temperatures, ensuring that it can mix with the marshmallow homogeneously.
Egg whites enable air bubbles
Even though sugar plays a crucial role in marshmallows, it alone cannot make a marshmallow because it lacks a crucial function: foaming capability. You can’t incorporate air bubbles within a sugar syrup, especially not ones that will remain there over time.
Egg white proteins on the other hand are exceptionally good at foaming. The proteins in the egg white can easily stabilize the air bubbles that you can incorporate by whisking the egg white. Meringues use this powerful functionality as well, and are actually quite closely related to marshmallows.
These proteins can do this so well because when they are whisking, they unfold. Each protein is essentially a long chain of different building blocks. Some of these want to sit in the water of an egg white, the hydrophilic regions. Others prefer to get into contact with the air bubbles, the hydrophobic regions. This way, they surround air bubbles in a way that stabilizes them within the foam.
Note, this only works with egg whites, not egg yolks. The yolk contains fats that can actually destabilize the egg white foam.
Heat stabilizes the egg white
An egg white foam will collapse over time if it is not stabilized additionally. In a marshmallow, this stabilization is done in two ways. First of all, the hot sugar syrup helps to stabilize the foam. The high temperatures help to ‘cook’ and set the proteins in the egg white. Much like how an egg becomes solid when you boil or fry it.
Gelatin keeps it stable over time
Secondly, gelatin adds an additional and crucial layer of stability.
Gelatin is also made up of proteins. These proteins work a little differently than egg white proteins. When gelatin cools down it can form a gel. It holds on to the surrounding water, firming up the marshmallow.
Gelatin can form very stable, firm, and most importantly bouncy gels. Jello puddings, panna cotta, they all get their wobble or bounce from the gelatin. As a matter of fact, it’s very hard to replicate this exact texture with any other ingredient. It’s why most gelatin-free versions of candy do have a different texture than that of their gelatin-containing counterpart.
Did you know that the ‘original’ marshmallow did not contain gelatin? Instead, it was made with marshmallow root, hence the name.
Over time the manufacturing process has also become more efficient, nowadays, marshmallows can be made continuously using a piece of equpiment called an extruder.
You can forget the egg white, but not the gelatin
Even though egg whites do help to make a very light, fluffy marshmallow, you can technically leave them out. The gelatin by itself is strong enough to form a foam and hold on to that foam for long periods of time. A marshmallow made without egg whites does tend to be a little firmer in texture, though also even more bouncy.
A tip for cleaning up
Undusted marshmallows tend to stick to just about everything. So be prepared for a seemingly daunting cleanup. But, don’t worry! Sugar, gelatin, and egg whites all dissolve decently well in water. Your bowl, tray, or any other surface that seems too sticky, just let it soak in water for a while and clean-up will be a breeze.
Listen to our marshmallow podcast episode!
Prefer listening over reading? Why not listen to our podcast episode dedicated to the science behind marshmallows?