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There seems to be a recommended minimum temperature for making ice cream of about -30C. But, the temperature of liquid nitrogen (-200C), which is often used for the same purpose, is much lower.

So, what is the harm in making ice cream using an outer freeze wall below -30C?

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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.

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  • I see. But, could the churning just be done faster to get back the optimum aeration and eliminate this concern in the end?
    – bobuhito
    Apr 17, 2021 at 19:26
  • I don't think so - at least a whole industry has decided to not pursue this. After all, there is some very complex physics involved in ice cream bases, so I don't think that you can randomly change parameters such as speed without getting a ton of unwanted consequences. They could have other reasons, sure - such as the avaliability of convenient refrigerants, or backwards compatibility, or a small number of producers - but my hunch is that it won't be easy to get optimal aeration just through added speed.
    – rumtscho ♦
    Apr 17, 2021 at 19:28
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    "I don't know the exact physics of liquid nitrogen ice cream and why it works well." I think that you might be onto something when you're talking about the boiling: not only is it providing aeration, but it's also probably boiling away before it can fully lower the temperature of the ice cream down to the temperature of the liquid nitrogen. If you look at the recipe for it in FuzzyChef's answer, you'll note that it involves adding small amounts of liquid nitrogen into the ice cream mixture and stirring until the liquid nitrogen boils away until you reach the desired consitency.
    – nick012000
    Apr 18, 2021 at 3:10
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    @rumtscho This argument neglects cost: it's entirely possible (and at least somewhat plausible) that the industry knows how to use liquid nitrogen well, but that it's vastly cheaper to operate at warmer temperatures, at little or no difference in quality.
    – Konrad Rudolph
    Apr 18, 2021 at 8:38
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    @KonradRudolph I am sure that the industry knows how to use liquid nitrogen :) When listing arguments, I was thinking more of incremental reduction of the temperature of a conventional freezer to maybe -40 or -60, not a jump to liquid nitrogen technology. And yes, cost can be a factor there too. Seeing how much people are willing to pay for a container of "premium" ice cream, if these temperatures would make noticeably better ice cream, producers would likely have started used them by now, with the cost being offset by the price.
    – rumtscho ♦
    Apr 18, 2021 at 9:01
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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.

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    And for today's useless trivia -- the ice cream churn mixing blade is called a "dasher", although for some reason, when you search for that term on the internet, it returns a lot of "dishers" (the scoops for serving ice cream)
    – Joe
    Apr 17, 2021 at 19:01
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    Just to confirm, you are saying that if my ice cream maker does not break, the lower the wall temperature the better? There is no minimum as far as taste and texture go?
    – bobuhito
    Apr 17, 2021 at 19:12
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    @bobuhito -- the custard would freeze solid. That's not ice cream. That's just ice.
    – Pete Becker
    Apr 17, 2021 at 22:16
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    @PeteBecker It wouldn't freeze solid because you're not adding enough liquid nitrogen to do that. Look at the first recipe linked to in this answer; you stop adding liquid nitrogen once your ice cream reaches the desired consistency.
    – nick012000
    Apr 18, 2021 at 3:11
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    You don't need any fancy equipment to make it other than the dewar to store the LN2. I've had it made at events using just a metal mixing bowl, and stirring implement. Depending on how much/how fast the LN2 was added the result could be anything from softserve to something similar to dipndots.
    – Dan Is Fiddling By Firelight
    Apr 18, 2021 at 5:26
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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.

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    Hi Randy, jpa is correct - we insinst on neutral language here. I cleaned up the tone, while keeping in the information you provided, it seems very useful.
    – rumtscho ♦
    Apr 19, 2021 at 7:02

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