What a machine does, and how to copy it
A churn freezer does two jobs at once. The University of Guelph’s Ice Cream Technology e-Book describes them: it pulls heat out of the mix, and it whips air in. It also scrapes the mix off the cold wall as it freezes, so the batch freezes in thin, fast layers.
Speed matters because of ice crystals. Guelph explains that faster freezing makes more crystals, and smaller ones. Small crystals feel smooth on your tongue. Big crystals feel gritty.
Air matters too. Guelph notes that ice cream can be up to half air by volume. Without a dasher, that air has to come from shaking, whisking or whipping.
So every method below copies a machine in one of two ways. It makes the cold colder, or it keeps the mix moving.
Ice cream in a bag
This is the classic method for kids, classrooms and campsites. Colorado State University Extension (Garfield County) gives this recipe on its “Ice Cream in a Bag” sheet.
You need:
- 1 cup light cream or half and half
- 1 cup heavy cream
- 1/4 cup sugar
- 1 teaspoon vanilla
- 1 quart-size sealable bag
- 1 gallon-size sealable bag
- 4 cups ice cubes
- 1/2 cup salt (kosher or rock)
- Oven mitts or a towel
Steps:
- Put the creams, sugar and vanilla in the quart-size bag. Seal it.
- Put the ice and salt in the gallon-size bag.
- Set the small bag inside the big one. Seal the big bag.
- Shake for 5 minutes. Wear oven mitts or wrap the bag in a towel, because it gets very cold.
The extension sheet says you get a soft ice cream you can eat right away or move to the freezer.
As a suggestion, press out extra air before you seal the small bag, and wipe the salty water off it before you open it. That keeps brine out of the cream.
Why the salt matters
Pure water freezes at 32 F (0 C). The Colorado State sheet explains that salty water freezes below that, so a salt and ice mix gets colder than ice alone. That extra cold freezes the cream fast enough to work in 5 minutes of shaking.
The ice and salt bucket
If you have an old hand-crank or electric bucket freezer, or just a pail and a metal can, the same physics works at a larger scale. The home-freezer guide in the University of Guelph e-Book (first published in 1980) gives the numbers.
The brine ratio
Guelph’s guide uses 1 lb (500 g) salt with 11 lb (5 kg) crushed ice for one pail. That is a ratio of 1 part salt to 10 parts ice by weight. Keep adding salt and ice in that proportion as the freezing goes on, then pour a little water over the ice.
How long it takes
The same guide gives 20 to 30 minutes of freezing, then a hardening stage. Fill the can no more than 2/3 full. The Nostalgia manuals for their 4 qt and 6 qt bucket machines say the same about the canister. The mix grows as it takes on air, so it needs that headroom.
Fixing a bad batch
Guelph’s troubleshooting is simple:
| What you see | What it means | What to do |
|---|---|---|
| Ice cream stays very soft | Brine is not cold enough | Add more salt |
| Coarse and icy in under 20 minutes | Brine got too cold too fast | Use less salt next time |
There is a limit to how cold salted ice can get. The Western Transportation Institute at Montana State University gives the coldest point for a table-salt brine as about -6 F (about -21 C), at 23.3% salt. A bucket at a 1 to 10 mix stays warmer than that.
Holding it without a freezer
Guelph’s guide says to plug the can, repack it with more ice and salt, and cover it with a heavy towel. Our own planning ranges say plain ice keeps ice cream firm for about 1 to 2 hours, and salted ice for about 2 to 4 hours. For longer holds, America’s Test Kitchen found that 4 half gallons packed with 5 lb of regular ice in a midsize cooler were soupy after 3 hours, and with dry ice they lasted 9 hours.
The Plan ice for a cooler button above opens our Dry Ice and Cooler Calculator. The calculators run in your browser, and the numbers you type are not sent to our server.
When you finish, rinse the salt off any metal parts. Guelph says this prevents corrosion.
Freeze-and-stir in a pan
This method needs only a freezer, a pan and a whisk. It is slower, and the sources for it are recipe sites, not universities.
The method as Barefeet in the Kitchen and Food.com describe it:
- Pour a chilled base into a shallow metal or glass pan.
- Freeze for about 45 to 90 minutes.
- Whisk, scraping the edges and breaking up frozen chunks.
- Repeat about every 30 minutes, for about 3 to 4 hours total.
- Freeze until firm.
Food.com says the stirring breaks up large ice crystals, that a whisk does this better than a spoon and adds air, and that a custard base with egg yolks helps stop big crystals from forming.
The science backs up the idea. Guelph’s chapter on hardening describes still, or static, freezing, and the e-Book explains that freezing rate sets smoothness. A pan left alone freezes slowly and grows big crystals. Stirring is how you fight that.
If you would rather skip the stirring, see our no-churn guide. The Open the no-churn base button above takes you to the Base Builder.
What about a blender or food processor
The sources we use do not cover a blender or food-processor method, so we can’t give you times or promise a result. The Cuisinart, KitchenAid and Ninja manuals cover only their own machines. The Ninja CREAMi owner’s guide is clear that the CREAMi is not a blender, and its pint must be frozen solid for 24 hours first.
A note on eggs
If your base uses raw eggs, cook it or use pasteurized eggs. The FDA Food Code requires pasteurized eggs in ice cream and similar recipes unless the egg mix is cooked to the stated temperatures. FoodSafety.gov gives 160 F (71 C) for egg dishes. Our custard guide walks through it.
Which method to pick
Our suggestions:
- Kids, classrooms, camping: ice cream in a bag. It is fast, cheap and hands-on.
- A crowd or a party: the ice and salt bucket.
- Just you, at home, with time: freeze-and-stir.
FAQ
Can I use table salt for ice cream in a bag?
The Colorado State sheet calls for kosher or rock salt. It does not say whether table salt works the same way.
Why is my bag ice cream still runny?
The bag recipe’s ice and salt amounts come from the Colorado State sheet. For bucket freezing, Guelph says soft ice cream means the brine is not cold enough and more salt fixes it.
How full should I fill a bucket freezer?
No more than 2/3 full. Both the Guelph home guide and the Nostalgia manuals say so.
Does freeze-and-stir really work?
Recipe sites like Food.com and Barefeet in the Kitchen describe it, and Guelph’s science on freezing rate supports stirring. No university source gives the method itself.
How do I keep homemade ice cream frozen at a picnic?
Pack it in salted ice. Our planning range is about 2 to 4 hours. For longer, consider dry ice and plan the amount with our cooler calculator.