Freezing. Crystals. Nitrogen. And why liquid nitrogen frozen ice cream are the smoothest.
Quick, what is the smoothest ice cream you have ever had? Chances are, it might have been one frozen by liquid nitrogen, which can freeze ice cream faster than you can say “freeze!”!
At its simplest, ice cream is simply a mixture of cream, milk, sugar, sometimes eggs, and other ingredients such as fruits and nuts. The mixture is then churned and frozen.
How smooth the ice cream is depends on many factors (e.g. how much fat is used), but a big part is how quickly the mixture freezes. The longer the mixture takes to freeze, the larger the crystals that form, the icier and rougher the texture of the ice cream will be.
Enter liquid nitrogen. Liquid nitrogen has an amazingly low boiling point of -196ºC/-321ºF. If we pour liquid nitrogen into our mixture at typical kitchen temperatures, it boils immediately. This has two effects:
1) The ice cream freezes instantly – as heat is rapidly drawn out of it by the boiling liquid nitrogen – and the size of the crystals formed are very small.
2) The vigorous vaporization (see all that vapor in the photo above?) also quickly aerates the ice cream as it freezes.
The result is a very smooth ice cream that is also fluffily yummy (see the video below to see the whole process)!
Moreover, as the video shows clearly, liquid nitrogen has the following additional advantages…
“…it is relatively easy to store as a liquid and pour over food or into a bowl. Because its viscosity is about one-fifth that of water and it has relatively low surface tension, liquid nitrogen flows rapidly into nooks and crannies…” (Source: Scientific American)
It is not just ice cream that takes advantage of this flash freezing advantages of liquid nitrogen. Fast freezing also prevents damage to the cellular structure of the foods being frozen, and hence is used on delicate foods like foie gras.
Freezing foie gras and other delicate foods instantly prevents further enzyme action on the food. Equally importantly, just like ice cream, if freezing is not done fast enough, the size of the crystals will grow. At some point, these crystals will pierce holes in the foie gras and break the cells. When it is defrosted and cooked, juices flow out and are lost (read all about it in the 1-Minute NomNom “You crack meat up“).
The use of liquid nitrogen is considered fairly new in the culinary world, and it is predicted that many new applications will be discovered. In the meantime, maybe we can just use liquid nitrogen to do some very fun things (see video above)!