Considering the last summer unbearable heat, and a not particularly icy winter, the “ice cream” topic continues to hold court, so let’s stay in theme with the previous article and say a few words about how to prepare a creamy liquid nitrogen ice cream, or rather, we’ll try to explain what happens from a scientific point of view during its processing.
Nitrogen (N) is a chemical element that makes up the majority of the air we breathe (about 78%). It is a gaseous element, odorless when at room temperature.
The most interesting feature for this article is that nitrogen condenses, i.e., passes from the gaseous state to the liquid state, at about −195.79 °C (77 K; −320 °F), in addition obviously to the fact that it is odorless and tasteless.
As you can imagine, therefore, handling nitrogen in its liquid state is not a bed of roses, because at that temperature even a few drops on your skin can freeze instantly, causing serious damage to your tissues. To quote cinema, it is a bit like what happens to the villain in James Cameron’s “Terminator 2: Judgment Day”, during the famous Arnold Schwarzenegger’s joke scene: Hasta la vista, baby.
However, since the purpose of this post is not to teach you how to prepare an ice cream with liquid nitrogen, but wonder that it is possible, we can fly over the technical difficulties of procuring, maintaining and using liquid nitrogen and pass directly to the part where, once our favourite flavour ice cream mix is prepared, we use liquid nitrogen to freeze it.
Considering the incredibly low temperature, a reduced amount of liquid nitrogen is enough for this freezing operation, but adequate to reach the ice cream container before its evaporation. In fact, at room temperature, the liquid nitrogen evaporates instantaneously, so expect to see a fine cloud of steam.
The liquid ice cream mixture in contact with liquid nitrogen freezes very quickly and this is the advantage of using nitrogen: the almost instantaneous freezing allows the creation of very small crystals, avoiding what we explained in the previous article, that is the formation of big grains.
Adding some more nitrogen little by little and constantly stirring it, you’ll get a perfect creamy ice cream!
The fast freezing process also allows the almost complete conservation of the nutritive elements of a substance, not only in ice cream, but in food in general, therefore, the liquid nitrogen could also be used to freeze food.
You can enjoy comparing the freezing times of the traditional “mechanical” process with the liquid nitrogen process at this site.
At the end of this Science of Cooking article, I feel obliged to go to the ice cream shop around the corner to…test the quality of their crystals!
Sources: Steve Spanglers
Matteo Biagetti | PhD Student @ Department théorique de Physique, Université de Genève