Who doesn’t love a marshmallow over the campfire? Marshmallow toppings and s’mores creations are all the rage in food trends this year, popping up on menus and shelves everywhere. It seems people can’t get enough of this nostalgic candy. Just in time for summer, let’s take a look at the food chemistry behind these unique treats.
History of the Marshmallow
Did you know the marshmallow is actually a plant? That’s right, the Althaea officinalis, or marshmallow plant, contains a thick, gooey substance in its roots full of various carbohydrates that both ancient and modern cultures have used to make sweet treats. Today, however, other ingredients are used to create gelation and the soft, foamy texture of the marshmallow.
The ingredients of a marshmallow are pretty simple: gelatin, water, sugar, corn syrup, salt, vanilla, powdered sugar, and corn starch. Some marshmallows may also contain egg whites for structure and strength.
What is gelatin? Gelatin is a protein found in animal collagen. It is used as a gelling ingredient that creates very strong gels and provides a “melt in your mouth” eating quality.
You may wonder why most desserts have so. much. sugar. Believe it or not, there’s often more to it than taste.
Take marshmallows, for example, there is a lot of sugar in these candies. In fact, they are over 50% sugar. So, what if you reduced the amount? What would happen?
Let’s break it down. Sugar is often the bulk of a recipe. Therefore, if you were to remove large amounts, it would need to be replaced with something else to end up with the same product yield. It makes foods tender and helps to incorporate air. High sugar content also helps extend product shelf life by decreasing water activity, or the available water for microbial and chemical reactions.
Reducing the sugar content will cause the marshmallows to flop. Literally.
Well, marshmallows are a special type of colloidal dispersion called a foam. A foam is air suspended in a solid. In this case, the gelatin protein expands to trap air within the liquid matrix and create a solid gel.
Guess what helps strengthen the gel and keeps that air suspended? You guessed it: sugar! Without sugar, the gel will weaken and the air bubbles will not remain dispersed in the solid gel matrix.
To put it to the test, I developed a formula, or scalable and reproducible recipe, based on this recipe by Alton Brown. I then adjusted this “control” formula to reduce the total sugar in the recipe by 25%.
The objective: to understand the role of sugar in the foam. Can the sugar be removed and create the same end result?
To make the marshmallows, first, the gelatin is hydrated with cold water. Cold water is necessary to allow the gelatin to hydrate and dissolve. If placed directly into hot water, gelatin clumps to itself.
Then water, sugar, corn syrup, and salt are heated to 240F to create a sugary syrup solution. This temperature is important to ensure the right amount of water is present in the syrup. Heating at this high temperature creates a supersaturated solution that holds more sugar than it normally would be able to as it cools down.
In marshmallows, different types of sugar are used in combination. Table sugar is a source of the disaccharide sucrose, while corn syrup is the monosaccharide glucose. Glucose is important to the formula because it prevents recrystallization of sugar in the candy that would otherwise cause a coarse, grainy texture. Gelatin also helps prevent the sucrose in the syrup from recrystallizing and ensures a smooth texture.
The syrup is then slowly added to the gelatin and beat at high speed for 13 minutes. The high speed mixing helps to incorporate as much air as possible into the product.
After the mixture is thoroughly whipped, it is spread onto a square pan or cutting board and left to set at room temperature for about 4 hours. This creates the foam, or air in solid.
You can then cut the marshmallows into any shape you like!
The control marshmallows are better than store-bought! They have more flavor and a tender, melty texture. The marshmallows are light and airy. They hold their shape well.
If you’re curious about the science of candy-making, this would be a great place to start!
Now, for the reduced-sugar marshmallows.
As soon as the test marshmallows are done mixing. I know something is different. The mass of sugar is solid, dense, and clinging to the whisk, whereas the control marshmallows were shiny, light, and almost pourable (see above).
After the 4 hour set period, I cut the marshmallow bricks into squares and rolled them in powdered sugar. Take a look at the cross section below for the results.
25% Reduced Sugar Marshmallow. Air cells are less uniform and are unstable in the foam, causing liquid to ooze out
You can see that the control marshmallows with optimized sugar are light and airy with an even distribution of air bubbles. The reduced sugar marshmallows, on the other hand, are less aerated, dense, and already starting to ooze liquid.
These marshmallows are less flavorful, and very gooey.They still taste good and have a decent texture, but they definitely won’t be stable enough to last very long.
What’s going on?
Remember that marshmallows are a foam, meaning air bubbles are continuously trapped in a liquid (and eventually, solid) matrix of gelatin proteins.
Proteins in the gelatin unravel once the hot sugar syrup is poured in. As the gelatin begins to set after whipping, it traps air bubbles in between the protein strands. Proteins act as great surfactants, or stabilizers, and can form stable gels on their own. However they are even stronger when sugar is added.
Sugar helps strengthen these interactions between the liquid and gas phases and creates stability. The sugar reduces the rate of drainage of liquid by increasing the viscosity (or thickness) of the liquid phase.
Without the right amount, air isn’t trapped in the foam to create a light texture. The marshmallows are not stable and the gel is more likely to collapse.
Why does the campfire make marshmallows gooey?
As you roast your marshallow over the open flame, there is a lot chemistry going on. Sugars are heated to high temperatures, leading to caramelization. This creates the golden brown color on the outside and many new flavor compounds.
Sugars known as reducing sugars are required for the caramelization we see on the crust. Monosaccharides such as glucose and fructose are reducing sugars, while sucrose (table sugar) is not. This occurs only when sugar is heated at high temperatures.
Meanwhile, as the heat from the fire continues to heat the marshmallow, the gelatin proteins begin to melt and uncoil. This releases the trapped air, leaving a delicious gooey center.
The same thing happens in your mouth when you eat a marshmallow at room temperature. The melting point of the gelatin gel is very low, and it begins to immediately break apart once it hits your tongue. That’s why marshmallows have a gooey texture in your mouth.
There is actually a lot of chemistry and science involved in food, even in something as seemingly simple as marshmallows. Reducing the amount of sugar isn’t as easy as it sounds and even minimal reductions can have a big impact.
Food scientists must understand the role of ingredients and production techniques to test new ways of producing products with less sugar.
Brown, A. 2014. Homemade Marshmallows. https://altonbrown.com/homemade-marshmallow-recipe/
Damodaran, S., Parkin, K.L., Fennema O.R. 2008. Fennema’s Food Chemistry Fourth Edition. CRC Press Taylor & Francis Group.