Can Ice Cream Maker Wall be Too Cold?

During freezing, you care about two parameters - crystal size and overrun. While people making ice cream at home will frequently tell you that smaller crystals equal softer ice cream, that's not exactly correct, especially when you can control the two parameters over a wider range. In reality, smaller crystals make smoother ice cream, while more overrun makes softer ice cream.

In the context of commercial ice cream freezing with a conventional freezer (not liquid nitrogen), if your ice cream freezes too quickly, it will be frozen before it has been properly frothed by the dasher, and you will end up with too dense ice cream. This is why commercial freezers are made on purpose in the -23 to -29C range. They could build them colder, but that is not desirable. This seems to be true over a wide range of technologies, since both batch freezers and continuous freezers operate at these temperatures. The amount of overrun is then controlled by dasher speed and dasher design.

I don't know the exact physics of liquid nitrogen ice cream and why it works well. I could imagine different scenarios: maybe people consuming it prefer low-overrun ice cream, maybe the boiling nitrogen introduces sufficient aeration, or maybe the dasher breaks it up into very fine pieces because it is so incredibly brittle. Possibly somebody with first-hand experience will comment on this. But it is a different principle than conventional ice cream preparation where you want to give your ice cream time to get churned properly before it freezes too much.

You can make ice cream with liquid nitrogen; in fact, this makes truly excellent ice cream if you have the equipment for it.

The last is the key, though. Home ice-cream makers are designed to operate and produce optimal creaminess at -10C or -20C. If you were to somehow fill one with liquid nitrogen, the custard would freeze solid before it agitated correctly, and the plastic mixer blades would break. So you can, and should if you can, make ice cream at a lower temperature, just not using your standard ice-cream machine.

The ice cream dasher is inconsequential when it comes to preparing ice cream. I run a stainless steel 7 inch dasher with liquid nitrogen pumped in by holes in the top of the mixer. The key is to not run the dasher for more than 13 seconds. To get the optimal crystal size without too little overrun, I use 1 cup of liquid nitrogen for every 10 cups of liquid milk. Mix for about 10 seconds and then you will have perfect ice cream every time. I am an ex Blue Bell employee and have experience with making ice cream under commercial conditions.