Cappucino au lait de soja

Source: http://www.scienceofcooking.com/foams/culinary_foams.htm a écrit:MILK AND CREAM FOAMS

What is the best type of milk to produce a foam?

As in the case of egg white foams it is the protein molecules that are responsible for milk being able to be foamed. And, as in the case of egg whites addition of fat will minimize the formation of foam. Foam stability decreases with increasing fat reaching a minimum at about 5% and then increases rapidly as fat is increased to 10%. At this point highly stable cream type foams form. Therefore 'skim milk' will produce the greatest volume and most stable foams, unless of course you go very high fat (35%) where whipping cream will also produce a very stable foam.

Why does milk foam?

There are two different types of proteins in milk: whey proteins and caseins with caseins making up 80% of the total protein of milk. Casein imparts good surface-active properties and thus plays a role in the functional properties of whipping/foaming. Whey proteins although offering less surface activity than casein, they offer far superior foam stabilizing properties creating a more rigid film at the air/water interface of the foam.

Both proteins are stable up to approximately 140F after which they become susceptible to denaturation. At this temperature new proteins are needed for stable foam so more milk must be added.

What Effect does Temperature Have on Foaming Ability?

Low fat milk foams best at low temperatures. This also applies to both whole milk and cream, although to a lesser extent. At temperatures about 100F, on up through to 160F the trend is reversed with the higher fat dairy products consistently exhibiting a greater volume of foam being produced at any given point. In general temperature trumps the influence of the fat on foaming.