What if ice cream never melted?

Ice cream comes out of the freezer cold and firm.

On a hot day it melts and drips down your cone. What if it never melted?

Ice cream is one of the best treats on a hot day, but it has a problem: it doesn't wait for you. Leave a scoop in the sun and it soon turns into a sweet puddle. That's why ice cream travels in freezers all the way from the factory to the shop.

So what if ice cream never melted? No drips, no puddles, no rush. But would it still be ice cream? In this lab we follow three clues: how ice cream melts, the fat and air bubbles inside it, and how we keep it cold.

Ice cream looks simple, but food scientist Douglas Goff of the University of Guelph calls it an incredibly complex multi-phase system: fat droplets, air bubbles, ice crystals and a concentrated sugar solution, all in one frozen foam.

This thought experiment imagines ice cream that never melts. To reason about it, we need to know what melting actually involves, which parts of the structure hold a scoop together, and why manufacturers and shops work so hard to keep it cold and at a steady temperature. Established food science and reasoned guesses are labeled separately.

Ice cream has tiny bits of ice, tiny bubbles of air and tiny drops of fat.

About half of a tub of ice cream is air!

Look at ice cream under a powerful microscope and you'd see four things: tiny drops of fat, tiny bubbles of air, tiny crystals of ice, and a very sugary syrup around them all. Douglas Goff, a food scientist at the University of Guelph in Canada, explains that about half of a frozen tub of ice cream is air.

The sugar does something important. It stops some of the water from freezing. Even in the freezer, part of the water stays as a thick, sweet syrup. That's why ice cream is soft enough to scoop, unlike a block of ice.

Goff describes ice cream as an emulsion of fat droplets that is whipped into a foam, about half air by volume in a frozen tub, and then partly frozen. Dissolved sugars depress the freezing point below 0 °C. As water freezes out as pure ice, the remaining solution grows more concentrated and its freezing point drops further, a process called freeze concentration.

The result, according to Goff's Ice Cream Technology e-book, is that even at a typical serving temperature of −16 °C only about 72 percent of the water is frozen. The rest remains a very concentrated sugar solution, which, with the air, is what lets ice cream be scooped and chewed at freezer temperatures.

Imagine a scoop that never melts. No drips on a sunny day!

But ice cream that never melts might never get soft and creamy in your mouth, either.

Now imagine ice cream that never melted. You could carry it in your bag, and it would never drip. Shops might not need freezers for it at all.

But think about what melting does. Ice cream softens as it warms in your mouth. Ice cream whose ice never melted, even there, might stay hard and icy, more like an ice cube than a creamy scoop. So 'never melting' might make ice cream less like ice cream. That is an idea, worked out from what ice cream is made of.

Imagine the two parts of melting separately. If the ice never melted, the scoop would keep its ice crystals even in your mouth, and its texture might stay icy rather than creamy; that is a reasoned guess, not a tested result. If only the foam never collapsed, the ice could melt while the shape held, which is closer to what food scientists can already influence.

A truly melt-proof ice cream would also remove the need for the cold chain, the frozen storage and transport from factory to shop. That might save energy and waste, but it would require ingredients and a structure quite unlike today's ice cream. All of these outcomes are ideas reasoned from its structure.

When ice cream warms up, its ice turns back into water.

Then the bubbles and fat let go, and the scoop slumps into a puddle.

Melting ice cream is really two things happening. First, the ice crystals melt. How fast that happens depends on the weather: a hot, windy day melts ice cream faster than a calm, cool one.

Second, the foam has to collapse. Goff explains that even after its ice has melted, ice cream doesn't slump into a puddle until the network of fat around the air bubbles gives way. Ice cream makers can make the foam stronger, so the scoop keeps its shape and melts more slowly.

Goff describes meltdown as two events: the melting of the ice, controlled by the outside temperature and the rate of heat transfer (faster on a hot, windy day), and the collapse of the fat-stabilized foam. Even after the ice crystals melt, ice cream does not collapse until that foam structure gives way, which depends on the extent of fat destabilization (partial coalescence), controlled mostly by the emulsifier concentration.

Emulsifiers such as polysorbate 80 increase shape retention and slow meltdown. Stabilizers, including locust bean gum, guar gum and carrageenan, add smoothness, reduce ice crystal growth in storage and provide resistance to melting. A never-melting scoop would push these effects to an extreme no real ingredient reaches.

Ice cream rides in freezers from the factory to the shop.

It must stay cold all the way. If it warms up and freezes again, it gets icy.

After it is made, ice cream is hardened in a blast freezer at about −30 to −40 °C. Then it has to stay cold in trucks, shops and home freezers.

It isn't only melting that matters. Goff explains that every time ice cream warms up and cools down again, the smallest ice crystals melt and their water freezes back onto bigger ones. After many ups and downs, the ice cream turns icy and crunchy. He says this often happens when ice cream sits out on a loading dock, in a shopping cart or in a grocery bag.

Goff's e-book describes hardening packaged ice cream in blast freezers at −30 to −40 °C, where most of the remaining water freezes. Below about −25 °C ice cream is stable indefinitely without ice crystal growth; above it, crystals can grow, which limits shelf life.

The main enemy is heat shock: temperature fluctuations during storage and distribution. When the temperature rises, small crystals melt; when it falls, the water refreezes onto larger crystals rather than forming new ones, so crystals grow and the texture coarsens. Shelf life, Goff writes, depends entirely on storage conditions: perhaps a year, or two weeks or less.