Have you ever looked closely at the label of your ice cream containers? If you did, you might have noticed ingredients on there that you don’t normally use when making ice cream at home. Often, these are called emulsifiers and stabilizers. Wondering why they’re in your ice cream and what they do inside your ice cream? Are they even truly necessary? We’ll be diving into the science of (factory made) ice cream, emulsification and stabilization!
Why stabilizers are added to ice cream
Let’s start with one of the two groups of ingredients: stabilizers.
A common way to make ice cream at home involves making a slightly thick custard (often using eggs or corn custard powder). Once you’ve made your custard you will aerate it (whip it up) and then freeze is. So why make this custard? Since the custard is slightly thicker than water (it has a higher viscosity) it will hold on to air more easily. Imagine whipping up pure water, this foam will collapse almost immediately, the air bubbles can escape very easily. However, in case of a custard the air bubbles will have more trouble escaping again. This is partly due to the increase in viscosity, but also due to the proteins and starches that stabilize the foam.
Without realizing, you’ve added stabilizers to your ice cream. The egg yolk proteins and corn starch serve as stabilizers. By increasing the thickness of the ice cream, or increasing viscosity, the mixture is stabilized. They also limit the growth of large ice crystals (remember, we want many small ones, not a few large ones), although they do not influence the overall ice crystal quantity (remember freezing point depression?). Another role of stabilizers can be that they reduce the ease of melting of ice cream. This is beneficial during transport for instance, but should always be taken into account. Using too much stabilizer can result in a gummy sensation because of a lack of melting! Overall, both stabilizers used by manufacturers as well as the ones you use at home have a similar function.
In commercial ice cream, often custards and the accompanying eggs aren’t used for making ice cream. Instead, manufacturers use other ingredients to stabilize their ice cream. Most stabilizers are so-called hydrocolloids and in most cases polysaccharides. These are large molecules that can hold on to a lot of water (and do their stabilizing job of holding onto water, preventing crystal growth, etc.). Their large structures will help them entangle with one another forming a gel-like structure. Most of them are also polysaccharides, being part of the group of carbohydrates.
Common stabilizers in ice cream
There aren’t actually that many stabilizers that are commonly used in ice cream. There seem to be three main ones, although this will also depend on where you live.
Guar gum & Locust bean gum
Despite their foreign sounding names these two gums naturally occur in nature. Locust bean gum can be found in the carob tree (grows in the Mediterranean) and guar gum comes from the guar bean (found in India)!
These two gums have a similar chemical structure but work slightly different. Both are long carbohydrate chains called galactomannans. These are long chains of mannoses (a sugar) with sidechains of galactoses (hence the name). The ratio of the galactose and mannose is what distinguishes the two.
Despite their similar structure, they behave quite differently, especially with regards to water solubility. Guar gum dissolves in water at room temperature, but locust bean gum will only dissolve at elevated temperatures. If you’re using these for your ice cream production that’s something to take into account for sure! Apart from their solubility they thicken a mixture slightly differently. Locust bean gum can form a gel by itself. Guar gum on the other hand will not do so, it will need an additional ingredient. Nevertheless, guar gum is a very powerful thickener, you need a lot less guar gum to create the same thickness compared to corn starch.
Another gum you might find in ice cream, which we won’t discuss in further detail here, is xanthan gum, often used in combination with locust bean gum.
Carrageenans can also be found in nature, however, instead of being found in land plants, it can be extracted from seaweed. Just like the two gums mentioned above it is a polysaccharide. However, this polysaccharides is sulfonated meaning that it has sulphate groups attached to it. Because they are also large (and flexible) molecules, they will also form gels. We’ve discussed carrageenan in more detail when discussing hot chocolate milk.
Why emulsifiers are added to ice cream
Emulsifiers are components that help mix water and fats together. Without emulsifiers fat and water won’t mix, instead, they will split almost immediately after addition. Emulsifiers prevent this from happening. Also, emulsifiers can do a similar thing when it comes to air bubbles in the watery ice cream mixture. They will stabilize these air bubbles. If you’d like to learn more, we’ve dived into the details of emulsifier science in a separate post.
In ice cream you are also trying to mix and stabilize a mixture of fat and water: cream + milk. The emulsifiers ensure that it forms one creamy consistency instead of a watery icy phase mixed with fat globules. You might not realize, but when you’re making ice cream using a custard, you’re adding emulsifiers to your ice cream. Egg yolks contain lecithin which is an emulsifier. Also the proteins in milk can act as an emulsifier in your ice cream.
Common emulsifiers in ice cream
The variety of emulsifiers in ice cream is slightly less than that of the stabilizers. The two main categories are:
- Mono- and diglycerides of fatty acids: as you might remember, fats and oils are triglycerides: a glycerol molecule with three attached fatty acid chains. Mono- and diglycerides also have this glycerol structure but they have only one (mono) or two (di) fatty acid chains attached to them. The glycerol section prefers to sit in the water, whereas the fatty acid chains prefer fat, thus keeping the two mixed.
- Lecithin: it sits in egg yolk but can also be derived from soy. In most cases this soy lecithin is what’s used in ice cream. Lecithin is a small molecule with a head and a tail. The head likes to sit in water whereas the tail likes to sit in oil. This way the lecithin will sit on the interface between the two and help stabilize them.
So, next time you’re eating a tub of ice cream, have a look and see whether you can identify any emulsifiers or stabilizers. Does your ice cream have any that are not in this list? Let us know! And in the meantime, enjoy your ice cream!
ps. Online you’ll be able to find recipes in the molecular gastronomy field that might actually add some of these ingredients to make a good ice cream. If you’re interested, give it a try and let us know how it went!
If you’re looking for very practical tips for more advanced ice cream making, have a look at this book: Hello, my name is ice cream, the art and science of the scoop, Dana Cree, link