Why homemade ice cream is icy, and how to fix it

What “icy” actually means

The University of Guelph’s Ice Cream Technology e-Book describes coarse or icy texture as ice crystals large enough to be noticed when you eat them. It calls iciness the most frequent texture defect in ice cream and the main limit on how long ice cream keeps.

Smooth ice cream is not free of ice. It has a great many small ice crystals of fairly even size, so your tongue does not pick them out. Guelph puts the average ice crystal in typical ice cream at about 50 micrometres across. Air bubbles are about 70 micrometres and fat globules about 1 micrometre.

Sandy is a different problem. Guelph explains that sandiness comes from lactose (milk sugar) forming crystals that do not melt in your mouth, so they feel gritty. If your ice cream feels like fine sand rather than shards of ice, see the storage section below. Quick hardening, a low and steady storage temperature and fewer temperature swings help with both problems.

1. Solids: too much water in the mix

Guelph’s list of causes for coarse, icy texture starts with too little total solids, which means too much water. Solids are everything in the mix that is not water: fat, sugar, and the milk proteins and lactose (milk solids-not-fat, or MSNF).

Guelph gives these targets for total solids:

For a mix with 10 to 16% fat, 9 to 12% MSNF and 14 to 19% sugars, Guelph gives a general range of 36 to 45% total solids.

Protein matters too. Guelph says proteins make up about 4% of the mix and hold water, which reduces iciness. MSNF also lets ice cream take in more air without turning snowy. But too much lactose brings back the sandy problem, so more is not always better.

Fat plays a part as well. The Ninja CREAMi owner’s guide says that when the proportion of fat or sugar in a recipe is too low, the result can be crumbly.

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2. Sugar: the reason ice cream can be scooped at all

If your homemade ice cream is too hard to scoop, look at the sugar first. Guelph explains that sweeteners, at about 12 to 16% of the mix, lower the freezing point. That keeps some water unfrozen even at serving temperature (Guelph gives -15 to -18 °C, roughly 5 to 0 °F). Without that unfrozen water, the ice cream would be too hard to scoop.

So cutting sugar in a recipe does more than change the sweetness. It leaves more water free to freeze into ice.

It can go too far the other way. Guelph notes that blends with high-fructose corn syrup lower the freezing point so much that the ice cream turns very soft at usual home storage and dipping temperatures. The Ninja owner’s guide makes the same point from the other side: too much fat or sugar can make the result too soft.

3. Freezing speed: cold bowl, cold mix

Guelph states the core rule plainly: faster freezing gives more, smaller crystals. Slow freezing, such as from a mechanically weak freezer, is on its list of causes for icy texture.

At home, the speed of the first freeze depends on how cold your machine and your mix are when you start.

Freezer-bowl machines. The bowl has to be frozen all the way through. Cuisinart’s booklets call for 16 to 24 hours, or 24 hours, depending on the model. KitchenAid’s use and care guide for its ice cream maker attachment gives a minimum of 15 hours. Both brands want the mix cold as well: Cuisinart suggests chilling it overnight, and KitchenAid says all batter recipes need to be completely chilled. Based on Guelph’s freezing-rate rule, a bowl that is not fully frozen or a mix that is still warm will freeze slowly and give bigger crystals.

Ice-and-salt bucket machines. A 1980 home-freezer guide hosted in the Guelph e-Book says that if the ice cream comes out coarse and icy in under 20 minutes, you used too much salt and the brine got too cold too fast. If it stays very soft, you used too little salt. The same guide says to use crushed ice.

Ninja CREAMi. The Ninja owner’s guide says to freeze the pint for 24 hours and to keep your freezer between 9 °F and -7 °F.

Air also counts. Guelph lists air in large cells as a cause of coarse texture. It also says that too much air (high overrun) gives a fluffy, crumbly, weak body that melts watery, while too little gives a gummy, pasty one. Guelph puts premium ice cream at 60 to 90% overrun and standard at 100 to 120%.

4. Ageing: rest the mix before you churn

Guelph lists too little ageing as a cause of icy texture. It says the mix should age at least 4 hours, and usually overnight, at or below 5 °C (about 41 °F). During that time the fat crystallizes and the proteins and any stabilizer take up water.

The 1980 home-freezer guide agrees in home terms: make the mix the day before for a smoother result and a higher yield.

Stabilizers belong here too. Guelph says the gums used as stabilizers thicken the unfrozen part of the ice cream and limit ice crystal growth, so ice cream made with stabilizer has smaller crystals at their largest. Too much gives a gummy body. Cuisinart’s booklet notes that homemade desserts lack the gums and preservatives of store-bought ice cream, so they turn out different and need time in the freezer to firm up.

5. Storage: hardening and temperature swings

Of all the causes on its list, Guelph calls fluctuating storage temperature “the most likely cause” of icy ice cream.

The reason is what Guelph calls heat shock. When the ice cream warms a little, the smallest crystals melt. When it gets cold again, that water freezes onto the larger crystals. The crystals get fewer and bigger, and every cycle makes the ice cream icier. Guelph names freezer defrost cycles and handling as sources of these swings, including ice cream left on the counter or in a warm car.

Hardening speed matters as well. Guelph says the colder the ice cream is when hardening starts, the faster it hardens and the smoother it ends up. Commercial blast freezers run at -30 to -40 °C. Below about -25 °C (about -13 °F), crystals stop growing. Above it, they keep growing at a rate set by the temperature. Slow hardening and re-hardening soft ice cream are both on Guelph’s list of causes.

For leftovers, the Ninja guide says to flatten the surface before refreezing and to process the pint again if it is hard after refreezing. By Guelph’s reasoning, any warm-up and refreeze is one more heat-shock cycle.

Our reading of all this: a home freezer without stabilizer gives you little control over hardening speed or temperature swings. What you can control is total solids, sugar, fat, ageing, a very cold bowl or brine, a shallow container, and how often you open the freezer door.

A short checklist for your next batch

These are our suggestions, put together from the sources above:

• Check your recipe’s solids and sugar against Guelph’s ranges before you start.
• Make the mix the day before and keep it cold overnight.
• Freeze the bowl for the full time your machine’s manual gives.
• Move the churned ice cream straight into a shallow container and into the coldest part of your freezer.
• Open the freezer as little as you can, and put leftovers back quickly.
• The 1980 guide says to freeze at least 3 hours before serving.

FAQ

Why is my homemade ice cream icy after a few days but fine on day one?

That points to storage. Guelph explains that every time the ice cream warms and cools again, small crystals melt and refreeze onto big ones, so it gets icier with each cycle.

Why is my homemade ice cream too hard to scoop?

Look at the sugar. Guelph says sugar keeps some water unfrozen at serving temperature, and without enough of it the ice cream gets too hard to scoop.

Why is my ice cream crumbly?

The Ninja owner’s guide says too little fat or sugar can make it crumbly. Guelph also links too much air to a crumbly, weak body.

Does chilling the mix overnight really help?

Guelph says the mix should age at least 4 hours, usually overnight, at or below 5 °C. Too little ageing is on its list of causes for icy texture.

Why does my ice cream pull away from the sides of the container?

Guelph calls that shrinkage, a separate defect from iciness. It ties shrinkage to very low freezing temperatures, storage temperature, too much air and pressure changes.