Learn the science behind:
Ice cream made with just 2 ingredients, made without using an ice cream maker, or even a stove? Real ice cream? Yes, you can make ice cream using only cream and sweetened condensed milk, in just 3 simple steps.
Since this method is so simple, it is the perfect vehicle to explain the science of ice cream. As such, we’ll be doing a deep dive into the role of cream and sweetened condensed milk. We’ll have a look at how they can take over the role of so many other ingredients!
- What is ice cream again (from a scientist's perspective)?
- 3 steps to make 2-ingredient ice cream
- Why use cream and sweetened condensed milk?
What is ice cream again (from a scientist’s perspective)?
In this article, we’re talking about ice cream that you can scoop into a ball. You know, the one you can place on top of a cone. We’ll also focus on ice cream that contains fat. There are many others types of ice cream, such as soft serve, sorbets, and popsicles, but to keep things simple we’ll focus on the former.
From a scientist’s perspective, this ice cream consists of 4 components:
- Air bubbles: air bubbles are important to make your ice cream scoopable and light. It’s a challenge to capture air bubbles into your ice cream!
- Water ice crystals: water freezes and hardens the ice cream. You want crystals for the ice cream to be sturdy, but not too much or it will become rock solid. The ice crystals should be small enough to prevent graininess (we discuss crystal size in more detail here).
- Sugar syrup: not all water in your ice cream freezes. Due to the freezing point depression some of it remains liquid as part of the sugar syrup. This ensures your ice cream doesn’t turn into an ice cube
- Fat crystals: all fats in ice cream are solid crystals. This is due to the low temperature. Fat adds creaminess to ice cream.
In a successful ice cream, you need enough of each component to balance the ice cream. They also need to be dispersed and mixed well.
3 steps to make 2-ingredient ice cream
When making ice cream, you’re creating and balancing the 4 phases. Often, you’d use a range of ingredients and process steps to do so. In this 2-ingredient ice cream, we only use 2 ingredients and 3 simple process steps. So, we have to be efficient! But how?
Our vanilla ice cream is made with 4 ingredients (milk, cream, egg yolks, and sugar) and way more than 3 process steps. Our olive oil ice cream needs 6 ingredients (milk, cream, sugar, honey, egg yolks, and olive oil). Even though both aren’t very complicated, they are a lot more complex than our 2-ingredient ice cream.We’re not counting ingredients purely added for flavor.
Step 1: Aeration
When you’re incorporating air into a liquid, as we’re doing when making ice cream, you’re actually making a foam. You can incorporate air by vigorously whisking the liquid: the air will get trapped within. However, foams are notoriously unstable. The air wants to escape from the foam. So, you have to find a way to make sure the air cannot escape the ice cream.
Traditionally, when using an ice cream maker you incorporate air while freezing the ice cream mixture. At the start, the mixture will be fluid enough to incorporate new air. While cooling down the mixture turns solid. As a result, it becomes harder to incorporate more air, but, the air that has been incorporated won’t be able to escape anymore.
In this 2-ingredient ice cream, we use a different trick: whipping up the cream! Cream with a high fat content is good at holding onto air. The fat globules in the cream stabilize the air bubbles that are whipped in. It’s not stable for long, after a few hours, whipped cream will have collapsed noticeably. However, for this recipe, we don’t need it to be stable for long, just long enough to make the mixture. Once frozen, the increased firmness will stabilize the air bubbles!
Air plays a crucial role in ice cream. It ensures you can scoop the ice cream and it will taste lighter, and melt a bit more easily. We discuss the role of air in more detail here.
Attention: do NOT boil the cream!
It is important that the cream you use is not boiled or heated – apart from well-controlled pasteurization processes. Additional heating of the cream destabilizes the cream. It’s very hard to whip the cream without it turning into butter!
Step 2: Mixing
Once you’ve incorporated air into the cream, all you need to do is mix in the sweetened condensed milk. It’s important to mix carefully. You don’t want to lose all those air bubbles you created in the first step!
Sweetened condensed milk is made by boiling down milk, to remove water, and adding plenty of sugar. It’s a thick liquid, but still fluid enough to easily mix through a whipped cream.
It is important to choose the ratio of cream : sweetened condensed milk well. Too much sugar will make for a very sweet ice cream. Too little will make the ice cream bland and hard.
You’re skipping several steps!
In ‘regular’ ice cream recipes you have to dissolve sugar. Also, you’d have to thicken the sugar + milk mix, often by making a custard (with or without eggs). By using sweetened condensed milk you can skip both these steps.
Step 2b: Mixing in cookies (optional)
You can upgrade your 2-ingredient ice cream to a 3-ingredient version by also folding in cookies pieces. Cookies don’t dissolve so aren’t part of your ice cream base. Instead, they add a separate “cookie phase”, alongside your other 4 phases. This adds extra flavor, and a little extra crunch – though the cookies will turn softer due to water migration.
Step 3: Freezing
All the hard work has finished! Now you only have to freeze the ice cream. Ideally you freeze it down to at least -18°C (0°F). In the freezer, some of the water freezes into ice crystals, the remainder will remain a liquid sugar solution. The low temperatures also solidify the fats, e.g. those in cream. This stabilizes your ice cream. It ensures that the air you incorporated doesn’t get lost.
Faster is better
To create a smooth, less grainy ice cream, it is best to freeze ice cream as quickly as possible. Manufacturers have special equipment to do so. Some ice cream shops use liquid nitrogen to freeze ice cream very rapidly. At home, ensuring your freezer works well and freezing several smaller batches instead of one large one can help.
By freezing faster you create more small ice crystals, instead of a few very large ones. A lot of small crystals give a smoother experience.
Why use cream and sweetened condensed milk?
Our ice cream consists of 4 components: air bubbles, water ice crystals, sugar solution and fat crystals. Since we only use 2 ingredients in this ice cream, each ingredient fulfills several roles.
Cream is made of milk and consists of two main ingredients: water and milk fat. Cream plays a role for the formation of 3 out of the 4 phases of our ice cream: air bubbles, fat crystals, and water ice crystals.
Stabilizing air bubbles
In this ice cream, the cream has to hold onto air. Not every cream can do so, only those with a high fat content of at least 30%. The fat particles in the cream are what stabilize and hold onto the bubbles.
Naming conventions for cream vary by country! In some areas high-fat creams may be referred to as ‘whipping cream’, ‘heavy cream’ or ‘heavy whipping cream’. If you’re unsure, it’s best to check the fat content on the nutritional label directly.
The fat in the cream has another important role. Aside from stabilizing air bubbles, it creates a rich, creamy texture. Fat melting on your tongue gives the ice cream a decadent feel. Just compare the experience of eating a popsicle versus a gelato!
Lastly, the water in cream will partially freeze, forming ice crystals. Upon eating ice cream, you can feel ice crystals melt on your tongue. It’s an important part of the ice cream eating experience.
Sweetened condensed milk
Recall that sweetened condensed milk is made by boiling down milk – thus evaporating moisture – and adding sugar. The high sugar and lower water content make it very shelf stable. The production process also gives it a characteristic dairy flavor.
If you’ve ever eaten pure whipped cream, you’ll know it tastes quite bland. Sweetened condensed milk adds flavor to the ice cream, both dairy flavors, as well as sweetness.
The sugar ensures that not all the water freezes, remember the freezing point depression? As a result, your ice cream will contain both pure ice crystals, as well as a liquid sugar solution.
If all that ice cream science has made you feel like ice cream, why not give the 2-ingredient ice cream a try yourself? You will see all that you learned come to life!