Cryogenic
Using liquid nitrogen to freeze ice cream is an old idea and has been used for many years to harden ice cream. The use of liquid nitrogen in the primary freezing of ice cream, that is to effect the transition from the liquid to the frozen state without the use of a conventional ice cream freezer, has only recently started to see commercialization. Some commercial innovations have been documented in the National Cryogenic Society Magazine "Cold Facts". The most noted brands are Dippin' Dots, Blue Sky Creamery, Project Creamery, and Sub Zero Cryo Creamery. The preparation results in a column of white condensed water vapor cloud, reminiscent of popular depictions of witches' cauldrons. The ice cream, dangerous to eat while still "steaming", is allowed to rest until the liquid nitrogen is completely vaporised. Sometimes ice cream is frozen to the sides of the container, and must be allowed to thaw.
Making ice cream with liquid nitrogen has advantages over conventional freezing. Due to the rapid freezing, the crystal grains are smaller, giving the ice cream a creamier texture, and allowing one to get the same texture by using less milkfat. Such ice crystals will grow very quickly via the processes of recrystallization, thereby obviating the original benefits unless steps are taken to inhibit ice crystal growth.
For similar reasons, good results can also be achieved with the more readily available "dry ice" and authors such as Heston Blumenthal have published recipes to produce ice cream and sorbet using a simple blender.
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