gelato’s states of matter
Gelato is a product more complex than it may seem and is the result of a delicate physical-chemical balance among the three different states of the matter that compose it:
Liquid state: water, which contains vitamins, mineral salts, parts of sugars, and proteins;
Solid state: fats, ice crystals, proteins, fibers, and stabilizers;
Gas state: small air bubbles that are incorporated into the gelato during the freezing process.
Water is the main ingredient in the gelato mixture since it’s also added in the form of milk, cream, fruit, and other ingredients.
In the preparation phase it’s used to solubilize sugars, to rehydrate proteins and stabilizers, to disperse fats, and spread aromas.
Once it passes from liquid to solid, it turns into ice crystals, giving the gelato its characteristic texture.
It’s important to remember that in any case not all the water inside the gelato freezes, some remains “free” as it allows maintaining the necessary malleability.
The size of the ice crystals is also an important factor: the smaller they are, the more the structure of the gelato will be fine, compact, and soft; on the other hand with thicker ice crystals the gelato will be grainy and cold. The size depends on the freezing process: if it’s fast (10 minutes with a professional machine) then they’ll be small; if it’s slow (45 minutes with a home machine) then they’ll be bigger.
Air is also a gelato component, and it’s much more important than you might think since it makes the gelato soft and pleasant: if there was no air inside, the gelato would be extremely cold and solid.
With a correct proportion, air gives the gelato a better malleability and a soft and not too cold texture at the moment of tasting.
The amount of air inside the gelato (and ice cream) is called “overrun” and usually, if we are talking about artisanal gelato, it shouldn’t be more than 40%. The term overrun is used to indicate the percentage of volume in excess of the initial value of the mixture.
However, care must be taken not to exaggerate the overrun as an excess of air causes a decrease in the flavors intensity present inside the gelato. The overrun is one of the main differences between gelato and ice cream because ice cream can have up to 110% overrun, which would mean that over half of its volume is air.