Pasteurization is without doubt one of the most delicate phases in the gelato-making process, and serves to reduce the amount of bacteria normally found in the mixture. Every foodstuff naturally contains a certain amount of pathogenic microbial flora which multiplies quickly at temperatures between 15-20°C and 55-60°C, whereas above and below those temperatures, bacterial proliferation slows down considerably.
Pasteurization is a heat treatment used to destroy spoilage agents and to give biological and enzymatic stability to foodstuffs, in this case gelato mixtures. Of course, during the process, the organoleptic qualities of the ingredients, i.e. the sugar, the semi-finished ingredients and other flavorings, must be preserved intact. During this phase, the gelato is heated to between 65 and 85 °C, and then rapidly cooled to just 4-5 °C.
Optimal pasteurization ensures that the gelato-making process is complete and safe from a food hygiene point of view. The pasteurizer is the piece of equipment used to perform this function, and the most modern models cover each step in the cycle, from mixing the ingredients to dissolving them, from heating to rapid cooling, from maturation to conservation of the mixture, until the time comes to freeze it, all in a single closed tub. A product that has been properly pasteurized is also far better from a quality point of view. Pasteurization also ensures that the flavorings and semi-finished products are at their best, as are the solubilization of the sugars and the hydration of the texturizers and proteins, while the fats dissolve and can be evenly distributed throughout the mixture, all of which leads to a perfect stable emulsion.
Homogenization takes place alongside pasteurization. As the term indicates, this phase serves to make the hand-made gelato mix uniform, harmonious and homogeneous. Whereas it is fairly simple to dissolve substances such as sugars and proteins in water, given that they are more or less hydrosoluble, it is far more difficult to mix components such as water and fats.
During the pasteurization cycle, when the mixture reaches 60-75 °C, the fats are broken down and amalgamated so that they can be homogenized. In order to help a homogenized mixture maintain its stability, emulsifiers can be added. These serve to reduce the surface tension by creating a stable emulsion – the result is an even softer, creamier mixture.
The whole pasteurization/homogenization cycle takes 2 to 3 hours.