Home Knowledge The Science Of Ice Cream – A Beginner’s Guide

The Science Of Ice Cream – A Beginner’s Guide

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The science of ice cream

As you cradle that waffle cone in your hand, happily eyeing off those scoops of ice cream on top, the science of ice cream may be the last thing on your mind. But if you enjoy making homemade ice cream, then having a basic understanding of how ice cream works is helpful knowledge to possess in the kitchen. It will help you create new flavors without relying on recipes, and you’ll find it much easier to troubleshoot why a method has failed on you.

Ice cream may appear very simple – milk, cream, and sugar is combined then frozen until hardened. But, the earliest frozen desserts have come a long way since 200BC when the first rustic ingredients were randomly tossed together. Science has dramatically improved the texture of ice cream, taking it from icy and granular, to what we now are accustomed to; a structure that maintains its shape on a cone or spoon yet melts in your mouth when eaten. It is this texture that’s the difference between regular and amazing ice cream.

What are the components of ice cream?

Ice cream is made up of all three states of matter: solids comprise of fat and ice; liquids are the solution of dairy and sweeteners; gas is made up of the air bubbles within the mixture. The relationship between the three is complex, and their balance is precarious. Get the mix right, and the result is creamy smooth ice cream. Get it wrong, and the texture will be unpleasant.

The goal of ice cream making is to create minuscule particles of ice and fat that support the air bubbles within a thickened sugary liquid solution. But how do we achieve this? There are five components that need to be emulsified in the correct quantities. Let’s take a look at these parts now.

1. Fat

The fat component within ice cream, referred to as butterfat usually comes from milk and cream. When ice cream is churned in a machine, the tiny fat solids form long strings that wrap around the air bubbles. You can’t see this with the naked eye, but it’s happening. Fat’s role is crucial as a stabilizer – it suspends foam, preventing it from slumping back into a liquid after churning.

A bottle and glass of milk.Although fat plays a crucial role as a suspension, it has more than one use in helping create delicious desserts. Fat is useful for:

  • adding a pleasant buttery mouth-feel
  • increasing the creamy richness
  • stabilizing the ice cream so that it doesn’t melt quickly
  • adding flavor to the mixture
  • releasing other flavors in the mixture

By law, ice cream must have 10% milkfat in the United States, although premium brands will have 16% or higher. An ice cream enthusiast, whether a commercial manufacturer or at-home novice, can dial the fat up or down by simply adjusting the cream and milk ratio. Whole milk only has around 3.4% milkfat, whereas cream can range up to almost 50%.

An ice cream low in fat will be light with flavors that are more intense but don’t last on the tongue. However, ice cream high in fat will be much richer and subtle in taste, with additional flavors lingering in the mouth for longer. For example, compare raspberry gelato and ice cream. The primary liquid in gelato is milk, which results in a relatively low-fat content and flavors which are intense. Ice cream, with its higher milkfat ratio will block some of that raspberry flavor; but, it will remain on the taste receptors for longer.

Practical advice for ice cream makers

Part of the fun when making ice cream is experimenting with ingredients. Adjusting the fat content to your personal preference is a good idea. You may also want to consider what you’ll be serving with the ice cream. If it is being served with a rich pumpkin pie, you may wish to dial-down the fat content so that the dessert isn’t too heavy. Adjusting the fat content can be achieved by changing the ratio of milk and cream. Adding more cream results in high fat ice cream; more milk leads to lower-fat ice cream. Adding too much fat will create an unpleasant texture similar to butter. Not enough fat and the ice cream will be hard, and it will melt too quickly.

2. Ice

Although it may not taste like it, ice cream is made up of microscopic ice crystals. This micro structure of solids provides the dessert with its body and firm bite. You can expect around 30% of ice cream to comprise of ice crystals.

Although fruit does contain significant water content, the majority of the water in ice cream comes from milk and cream. This water is what transforms from a liquid to solid as it freezes.

The best ice cream is always smooth in texture. This consistency can be achieved by keeping the ice crystals as small as possible. Larger crystals will result in an icy, coarse texture while tiny crystals provide a smooth mouth-feel.

Ice crystal size also affects the ice cream’s texture. The larger they are, the colder it feels in the mouth. Making a dessert that’s too cold will dull down its flavor, which isn’t ideal.

Practical advice for ice cream makers

As an ice cream maker, using a suitable recipe with the right ratios will play an essential role in good ice cream. The method of freezing is also a crucial part of making the ice cream. Imagine mixing the ingredients then putting them directly into the freezer for a few hours. The result would be a rock-like texture as the crystals were allowed to freeze unencumbered. However, by using an ice cream maker, the paddle churns the mixture, breaking the crystals into smaller pieces as they freeze. The best ice cream makers are very effective at freezing the ingredients fast, resulting in tiny crystals.

​3. Air

The gas component of ice cream is air, which plays an essential role in the creation of ice cream. The scoopable texture and soft consistency are made possible by incorporating air into the mixture.

  • Increased air provides a less creamy, but lighter texture.
  • Reduced air provides a creamier, denser texture.

Air adds volume to ice cream and is measured as overrun. It is a useful metric for understanding how much of the ice cream is the original liquid, and how much is air. If we start with two quarts of ice cream base and, after churning, the volume is now three quarts, the overrun is 50%.

Different types of frozen desserts have varying levels of air added. Gelato is whipped at a lower speed to add less air, while frozen custard and ice cream have more air incorporated.

To be called ice cream in the United States, it must have less than 100% overrun.
Premium brands must contain less than 50% overrun.

Does less overrun result in a better-tasting dessert? The answer comes down to the individual’s taste preferences. Many would prefer a regular pack of fluffy Breyer’s vanilla ice cream over a pint of dense Ben and Jerry’s.

Practical advice for ice cream makers

Commercial ice cream makers have the ability to dial-in the required overrun, thanks to the use of high-tech, expensive ice cream machines. The faster the dashers (mixing paddles) rotate, the more air is whipped into the freezing liquid.

The cheapest ice cream in the supermarket will usually have very high overrun, sometimes over 100%. This is a cost-effective way to increase profit since air doesn’t cost anything. Premium ice cream has lower overrun, which is why it is denser.

For the at-home amateur ice cream maker, overrun is challenging to manipulate as domestic ice cream makers have only one speed. These machines provide overrun of somewhere between 15-30%. You are better to focus on the other components of ice cream. If you ever get serious about craft ice cream, look to invest in a commercial machine.

4. Sugar Solution

A sugary solution, known as a matrix, acts as the liquid in ice cream. Its role is to suspend air, fat globules, and ice crystals. A sugar solution is made up of protein, sugar, and water.

Protein mostly comes from dairy ingredients. Around 4% of milk is protein, which is essential for providing the flavor we associate with dairy. Protein also acts as a stabilizer, helping the fat trap any air bubbles nearby. Egg yolks also contain a source of protein.

Skim milk powder isn’t overly common in recipes for making ice cream; but, it is advantageous. It increases the protein and lactose in the mixture without increasing the water content. If you are working on a low-fat ice cream that doesn’t use a lot of cream, skim milk powder is a good option for increasing the protein.

Sugar can be found in dairy ingredients, but the majority of sugar is added separately. Sugar is essential for sweetening the ice cream, and for providing a soft texture. The most common sweetener is sugar, but there are many other options. Honey, maltodextrin, sucrose, and treacle are a few alternatives. Each option has differing levels of sweetness – they are all compared to sucrose in relative terms (relative sweetness). A sweeter sugar has a higher number.

Maltodextrin in a spoonSugar plays a vital role in stopping the formation of large ice crystals by reducing the freezing point of water. The larger the quantity of sugar added, the fewer ice crystals will form. As with every ingredient used in making ice cream, there is always a trade-off as more is used. In the case of sugar, adding too much will cause an unpleasant, overly sweet dessert.

Water comes from milk, cream, and additional fruit, which contains water. Although much of this water will freeze, some remains as a liquid. As the water contains sugar, the freezing point is reduced, allowing some of the water to remain a liquid, even after freezing.

Practical advice for ice cream makers

There is a wide range of sugars that can be used in ice cream, all of which produce different levels of sweetness and affect its structure in various ways. For those trying to reduce sugar in their diet, simply cutting out the sugar isn’t possible as the structure will fail.

5. Other solids

Other solids can also be added to ice cream such as salt, chocolate, candy, and cookies. These contribute flavor as well as structure and texture. Solids reduce “free-roaming” water in the ice cream and so the number of large ice crystals is also less.

Brownies add texture and flavor.Practical advice for ice cream makers

Adding additional solids can help improve the ice cream. But, adding too much isn’t advisable – you’ll transform creamy ice cream into a weird texture that could be become grainy or sweet, or simply create a texture that no longer resembles ice cream.

​The role of emulsifiers

An emulsion is where two or more ingredients come together when they wouldn’t usually mix. Making mayonnaise from egg yolks and olive oil is an excellent example of an emulsion. Typically, these two would separate, but if the oil is slowly added and whisked at top speed, they come together to make a tasty sauce.

An everyday emulsifier used in ice cream is egg yolks, which contain lecithin. They help the fat globules to cluster together, resulting in smoother ice cream, which takes a lot longer to melt than the same ice cream, without yolks.

Other ingredients work as emulsifiers. Italians prefer to use cornstarch when making gelato as it allows the flavor of the other elements to remain untainted by the egg yolk flavor.

In commercial ice cream, some premium brands use egg yolks during production. However, the majority of manufacturers use other options like Polysorbate 80 instead.

The role of stabilizers

Stabilizers help to thicken the ice cream by absorbing excess water. They are useful for improving the ice cream’s structure, especially once removed from the freezer. The addition of a stabilizer will allow ice cream to remain out of the freezer for much longer without melting. Also, ice crystals won’t form as easily in the freezer, so you’ll maintain a creamy texture for much longer in storage.

Some common types of stabilizers include guar gum, locust bean gum, xanthan gum, and carrageenan. They each have different characteristics, and it is common, in commercial ice cream, to see a combination of at least two different stabilizers.

If you decide to use one of these ingredients at home, you’ll only use tiny amounts and adding them requires care. It is best to blend the powder into sugar before adding to any liquid. If you add more than a few granules together to liquid, it will form an unpleasant clump and will need to be discarded.

Summing up

If you love to make ice cream, or just love chemistry, then learning the science behind ice cream is well worth your time. An ice cream enthusiast will gain a deeper understanding of how ice cream is made and will find it easier to create their own recipes. Combining a scientific approach to making ice cream with some artistic creativity, and you’ll have the foundation for making some excellent desserts.

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