Biochemical characteristics of cappuccinos made with high-quality pasteurized milk and UHT milk at different steam injection conditions

This Eureka project arose from the collaboration between the University of Camerino (UNICAM) and the Simonelli Group company (Belforte del Chienti, Macerata, Italy), a company specialized in the production of coffee machines. From this collaboration derived also the "Research & Innovation Coffee Hub" (RICH), a heterogeneous group of researchers who aim to study the chemical-physical, nutritional, organoleptic properties of the products (mainly coffee and cappuccino) obtained with the use of the coffee machines produced by the company, and also to optimize the coffee extraction procedures. The ultimate goal is to obtain high quality final products dispensed by increasing the performance of the coffee machines. Espresso coffee has, over the years, reached global popularity and appreciation. Most of the Italian coffee machines are destined abroad, considering that 3 out of 4 machines are sold in other countries. There is a continuous commitment to improve the quality of the product on the Italian market and at the same time to spread abroad a greater culture of espresso coffee consumption. The same is true for the cappuccino, which is the most consumed beverage both in Italy and in other countries, for which a continuous improvement of the product is required especially regarding the visual aspect, the foam stability, and the organoleptic properties. In particular, for the international market, milk-based drinks represent about 80% of total drinks (Milk; Flat white, characterized by less foam; espresso; cappuccino). Milk and Flat white require a different foam than cappuccino with thinner bubbles and a more liquid final. Furthermore, in the international market, another aspect to consider is the “take- away milk-based drinks” which, unlike cappuccino that is normally prepared in a glass cup, are prepared often in paper/plastic cup and at higher temperatures (70-75° C) with consequences on the chemical-physical and organoleptic characteristics. With this in mind, innovations in espresso machines are constantly evolving, especially in the direction of ergonomics, energy efficiency, design, and temperature stability, but it is important also to know the changes occurring in milk during the preparation of cappuccino and/or milk-based drinks. This research project fits in this context, with the main objective of obtaining a cappuccino preparation of high organoleptic quality and with peculiar chemical-physical and nutritional properties. Usually, a traditional cappuccino is made of 25 ml espresso and 100 ml steam-foamed milk growing to a volume of about 125 ml. To get a high-quality final product, the selection of the raw material is very important, the cow milk used should have 3.2% minimum protein content and 3.5 % minimum fats in order to get the perfect balance of fat and proteins that ensures good taste and creamy foam with a good texture.Furthermore, it is very important the temperature at which the milk is whipped: should not exceed 70° C otherwise the milk takes on a "cooked" flavor due to the "caramelization" of lactose, and the proteins present in the milk undergo a process of denaturation which leads to the exposure of sulfhydryl groups which can alter the taste of the beverage itself. In a high-quality cappuccino, the foam should be compact and creamy, with a fine texture and shiny surface. The foam of the cappuccino is a colloidal dispersion of a gas in a liquid, the liquid is the milk used for cappuccino, while the gas consists of the air and water vapor used to whip the milk. The air droplets can form a colloidal dispersion in the milk thanks to the presence in it of surfactants that in the milk is represented by proteins (mainly caseins) and phospholipids. The stability of the foam depends on the relative concentration of surfactants. The higher it is, the more stable the foam, as the gas droplets are small and well separated from each other. Therefore, if the concentration of fats like triglycerides (which are not surfactants) is low, the foam of the cappuccino is more persistent. In whole milk the percentage of fat is around 3.6% so to obtain a creamy and above all stable foam it is important to be able to disperse as much gas as possible during the heating time due to the steam blown into the milk. This is obtained starting from a milk temperature of about 5°C (refrigerator temperature), as the temperature rises (to reach the temperature of 60°C), the milk proteins are partially denatured, contributing to the stabilization of the bubbles in the cappuccino foam. Finally, in a high-quality cappuccino, the cream should have a thickness of about one centimeter in the cup; this requires a greater injection of air and steam to be incorporated in the milk in the subsequent phase of micronization of the bubbles at the beginning.