The science behind the scoop (and how to stop it from melting)
Around the world, ice cream is a popular dessert. It’s been enjoyed for centuries and is loved by many. But ice cream has a downfall – it melts. There's nothing quite like the panicked licking as you try to keep up with your melting cone on a hot summer day as sweet rivers of ice cream try to escape and turn your fingers into a sticky mess.
So, we know it melts, but why? And, can we win this battle? Is there really a way to make ice cream not melt while you're trying to enjoy it? Stick around, we’ve got a bit of science to scoop out. Want the short story instead? Scroll to the end for the TL;DR.
Let's dig in
Ice cream is typically made from milk fat (at least 10% to qualify as ice cream in the US), sweeteners, flavorings, emulsifiers (to keep it from separating), and stabilizers (that work to slow melting and increase creaminess – by preventing large ice crystals from forming).
We end up with 3 main structural components – air cells, ice crystals and fat globules. A smooth, creamy ice cream that resists melting (at least for a while) calls for a perfect harmony between these components.
First, let's look at the ice crystals. Ice crystal size is a critical factor in the perceived creaminess of your ice cream. Science has found that, ideally, the ice crystals should be very tiny – just 10-20 µm in size. Any bigger and a grainy or icy texture will occur.
Next, let's discuss the air content (often called overrun) and air cell size. During churning, air is incorporated into the ice cream base, contributing to its smoothness and density. Air cells also act to insulate the ice crystals from heat, and smaller air cells do a better job than larger ones.
The final factors in melting are the fat content, globule size and distribution. Ice creams with higher fat contents tend to be softer and melt slower than their lower fat counterparts. During freezing, some of the individual fat globules join together and form destabilized fat globule clusters (through a process known as partial coalescence). An ice cream with more destabilized clusters will melt more slowly and have a creamier mouthfeel. The fat clusters surround and support air cells, keeping them evenly dispersed.
Stabilizers, when used, mainly work to increase the viscosity (or thickness) of the ice cream base, which gives the final product a creamier texture. Thicker products also melt more slowly.
Back to the melting…why does ice cream melt?
As the tiny ice crystals melt, liquid flows through the spaces between air cells and fat globule clusters. If there are fewer fat clusters, they will get swept away in the melted ice crystal flow, and the structure collapses (aka melts). If there is a high concentration of fat clusters, they get stuck on each other and can’t get swept away in the ice crystal flow so the structure remains relatively intact (like how those ice cream sandwiches suspiciously don't melt).
The proportions of air, ice crystals, and fat used in ice cream determine its melt rate. There is no ideal recipe for the perfect ice cream, and manufacturers adjust these components to customize their ice cream. This is why some ice creams melt quickly, while others never seem to melt at all.
Why does ice cream melt faster on a hot day?
Of course, no article on ice cream melting would be complete without discussing temperature. Where does it fit in? As the temperature rises, the ice crystals will melt faster, which, in turn, leads to a faster collapse of the ice cream structure - the tragic phenomenon we call melting.
So, how can you stop ice cream from melting?
We're not into eating our ice cream in a freezer, or finding some arctic climate to keep our treats cool (although we firmly believe that it's never too cold for ice cream). Even though there are a few tricks to help keep your ice cream solid - dry ice, freezer packs, wrapping it in aluminum foil - none of these are very practical while you're eating your frozen treats. That's why we created a solution to delay melting - at least for a while. Calicle insulated bowls use vacuum insulation to block heat from the surrounding environment from reaching ice cream through the bowl walls. This keeps those ice crystals cool so they don’t melt and the ice cream retains its delicious shape and texture. These bowls do allow for some heat transfer at the top (less with the lid on), so our treats do tend to soften on the top first. Since we couldn't enjoy our ice cream if it was in a fully sealed container, we're willing to accept the trade-off. Not to mention, it usually disappears before it becomes a concern.
TL;DR
Ice cream contains tiny ice crystals that are surrounded by air cells and fat globules. As temperatures rise, these ice crystals melt and the structure is destabilized, which we call melting. The warmer the temperature, the more quickly the ice crystals melt, and the more melting we see. Calicle cups slow the ice crystal melting by keeping the ice cream cool so you can enjoy it without meltdowns.
References:
The importance of fat in ice cream. (n.d.) Dream Scoops. Retrieved 20 February 2022, https://www.dreamscoops.com/ice-cream-science/fat-in-ice-cream/
Porto, R. (2019, September 19) Why are Stabilizers Used in Ice Cream. Ice Cream Science. Retrieved 20 February 2022, http://icecreamscience.com/stabilizers-ice-cream/
Porto, R. (2016, March 8) Why Does Ice Cream Melt? Ice Cream Science. Retrieved 20 February 2022, http://icecreamscience.com/ice-cream-melt/
Warren, M. & Hartel, R. (2014, March 8) Why ice cream melts. Dairy Foods. Retrieved 20 February 2022, https://www.dairyfoods.com/articles/90311-why-ice-cream-melts