Ice cream bars seems to become more and more fancy. They used to be a creamy center, on a stick, with a simple chocolate or fruity layer around them. However, nowadays there are ice cream bars with up to three layers covering the ice cream, caramel, chocolate, maybe even something fruity or nutty. The centers themselves aren’t always plain ice cream any more, they can have a swirl of flavour in them! Have you have wondered how these are made? How do they get that nice smooth coating (or even several layers of coating) around it? Or how do they manage to insert a stick into the ice cream?
We certainly have, so we dived into books and scrolled through YouTube to figure out exactly how they’re made!
The challenges of an ice cream bar
If you have a look at your ice cream bar (or the one on top of this post) you might notice a few properties that make this bar pretty hard to make. First of all, the shape. The ice cream bar has an oval shape. This shows that it most likely wasn’t made in a mould. If it would, the mould would have to open somehow or it won’t come out. Then there’s the stick. Apparently, there’s a moment during production that the ice cream is firm enough for the stick to stay in place, but still soft enough for the stick to even go into the ice cream center. No worries, we’ll come back to this later.
Then of course, there’s the coating. You can imagine that a chocolate coating is still relatively easy to make, you could dip the bar into some chocolate. But how do they create that caramel or fruity layer around an ice cream bar? We’ll be going through all of these challenges, one by one.
Making the center
Of course, before you can make the center of your ice cream bar, you’ll have to make the ice cream itself. We’ve discussed the details of making ice cream on a factory scale in a separate post. When making ice cream the most important bit is that enough air is incorporated into the ice cream and that enough small ice crystals have been formed. Shortly after the ice cream has been made it can still be quite flexible and soft, it will only harden by freezing it at low temperatures for a longer period of time. If you’d want to make an ice cream bar, you’d definitely want to make the center before hardening the ice cream.
Extruding ice cream
In large scale manufacturing this shaping step can be done using an extruder. An extruder is essentially a pipe with screws inside through which the ice cream can be transported. The end of the extruder will have a die. This die will have the final shape of the ice cream bar, in this example an oval. When the ice cream is pushed out of the equipment a hot thread will slice of the required thickness of the center. As a result you end up with thick slice of your desired shape (oval in this case, but it could also be the shape of an animal for instance)
Since the ice cream still has to be shaped and passed through the extruder it will still be somewhat soft and flexible. Therefore, it is still possible to insert a stick into the center at this point. That said, the ice cream will be firm enough to keep its shape when it’s transported further onto the cooling belt.
Rheology as a tool
When making an ice cream bar it is important for the manufacturers to properly understand the flow behaviour of the ice cream center. If it’s too liquid it won’t keep it’s shape when it comes out of the extruder. However, if it is too stiff, it cannot be pushed through well. Manufacturers can use rheology to determine whether the ice cream has a suitable consistency. Rheology describes the flow behaviour of a material.
If the flow behaviour isn’t correct, there are a lot of parameters a manufacturer can try to improve. One of those is the ingredients of course. But there are also process parameters that can be tweaked to improve the flow properties. For instance, by lowering the temperature the ice cream will become harder. By stirring more or less, the number of crystals can be influenced.
Making the chocolate & caramel layers
Once the center has been made, it’s time to start thinking about applying those delicious outer layers onto the ice cream! This starts be cooling down the ice cream center further. The ice cream wasn’t too cold or solid yet at the point of extrusion, however, now it has to set more firmly so it will hold its shape well.
To create a chocolate layer the ice cream is then dipped into warm chocolate. The stick comes in handy here, since it can be used to dip the centers into the chocolate. The chocolate itself will be warm and liquid so it flows well. As soon as the chocolate touches the cold ice cream center a thin layer of chocolate will form around the ice cream. The chocolate will set immediately and thus the dip won’t take long. The ice cream and chocolate will be cooled together to further firm up the chocolate layer.
When dipping in the chocolate, it is very important that the rest of the chocolate in the dipping bath doesn’t set. Therefore, the chocolate will always be kept in motion and the dip won’t last too long.
Multi layer ice cream bars
Some ice cream bars don’t just have a chocolate layer, instead they might have several layers around the center. Often the first layer is a chocolate type layer. This is a layer with a high fat content. The high fat content serves as a barrier between the next layer and the ice cream center. If this layer wasn’t there, the moisture of the next layer and the ice cream center would move from one to the other (we discussed the details of this phenomenon before).
Even though this first layer is important to keep the ice cream fresh, it does make it harder to apply that second layer! You now have an ice cream center with a thin outer chocolate layer. This outer layer is more prone to melting than the cold center was. Therefore, it often cannot be dipped again in the same way as before.
Caramel & fruit layers
When you apply a caramel or fruity layer on the ice cream you want it to stay sufficiently liquid and soft so it eats nicely. Whereas chocolate should crackle and become snappy, a fruity or caramel layer will never become snappy. Instead, it would become as hard as ice. Luckily, both types of layers both contain a lot of sugar. The high sugar content of the layers lowers the freezing point of the layers. In other words, they will not become rock solid.
For the consumer this is a good thing. However, it does make it harder to apply the layer. Whereas the chocolate layer sets immediately when brought into contact with cold ice cream, the fruity caramel layers will not do so so easily. One of the solutions used to overcome this is to freeze the ice cream centers even further. For that purpose liquid nitrogen can be used. Liquid nitrogen is very cold, -195C. By dipping the ice cream centers into the liquid nitrogen, they will become extremely cold. They are immediately dipped in the caramel or fruity layer. Because the center is so cold, the liquids will freeze in a thin layer around the center.
Depending on the exact composition of the product they may be dipped into liquid nitrogen again to help solidify the layer. Also the cycle might be repeated to get a layer of the desired thickness.
Of course, manufacturers are continuously trying to improve their processes and come up with new smart innovations. Their technology may well be a lot more advanced than we discussed here, nevertheless, hopefully this gave you a nice sneak peak into the world of food manufacturing!
In the video below (which we found on YouTube) you can find a re-cap of the process we just described. The video starts by showing how the centers are formed and how a stick is inserted. Next they are frozen to become solid and even colder. Then they are ready to be dipped into a chocolate bath. Notice how the chocolate continues to flow all the time, this is to prevent the chocolate from setting anywhere else but on the ice cream center itself. The bars are then cooled another time, to allow the chocolate to set before being packed.
The science of ice cream, Chris Clarke, p. 104-108, link
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Patent: Coated frozen confection, US20170238577A1, link
Patent: Process for coating frozen products, link
Patent: Coated frozen confection, WO2016001099A1, link