The maturation process requires the mixture to be kept at a temperature of about 4-5°C under continuous stirring. This phase helps the mixture become denser, making it easier to incorporate air during the subsequent freezing process, and allowing more water to be absorbed by the solid ingredients.
A proper maturation process will enable the proteins in the mixture to absorb free water content in the form of water of hydration. Complete hydration of the solids, in particular hydration of the proteins in the milk, eggs and ingredients, is vital. Good gelato products need to be fully hydrated as this creates a finer, more spreadable structure, and proper maturation averts the danger of building up large ice crystals, which make for a coarser and less enjoyable product. At the same time, the fats harden and crystallize, which is the best way of incorporating air into the finished product.
Until a few years ago, it was believed that mixtures had to mature for 48-72 hours, which made this key phase quite challenging. A new generation of stabilizers have enabled us to reduce those times down to 4-6 hours. However, it is good practice, if the aim is to make top-quality hand-made gelato, to mix the ingredients together in the pasteurizer in the evening and then pour it straight into the churn so that it is ready the next morning, which helps it to age for much longer (12-14 hours).
Finally we come to the batch freezing or chilling phase, which is when the hand-made gelato transforms from liquid to solid. This requires three different actions to take place: the mixture first needs to be churned, then cooled and then filled with air. This is undoubtedly one of the most important phases in making gelato: indeed, most of its quality and yield are a consequence of this stage.
What happens during chilling? Chilling involves freezing the water, which thus changes from liquid to solid. The mixture is cooled down while it is being stirred and in the presence of air, abruptly dropping from 4-6°C to approximately -15°C, while the free water solidifies to create a solid pasty substance, i.e. gelato. A sudden drop in temperature is required in order to prevent the build-up of water crystals, so as to obtain a smoother and less icy texture. Continuous churning of the mixture also helps to incorporate air and increase its volume.