The perfect foam for a cappuccino should have small bubbles not visible to naked eye. It should be silky, compact and creamy.
To obtain this consistency you should have to consider that fats are bad for the stability of the foam. This means that the best solution should be to use a skimmed or semi-skimmed milk with a percentage of fats between 0,1 and 1,8%. It’s really difficult to use full-fat milk because the percentage goes up until 3.6%.
On the palate the difference is big, for a matter of taste you should have to use full-fat milk.
To avoid any problem is necessary to disperse as much gas as you can during heating time. To make this possible, is mandatory to use a 4-5°C cold milk.
The only way to have such temperature is to use a compressor milk cooler (discover here the Vitrifrigo range). Other technologies as absorption or thermoelectric are not adapt because of the performances, they can modify organoleptic properties of the milk.
Maintaining the milk at 4°C won’t allow the air to dissolve in the liquid. When the temperature will rise, milk proteins will denatures and this contributes to stabilizations of the bubbles. Moreover, you will have more time to create the foam before the milk will reach the right temperature.
When the temperature is 65°C it’s possible to put the foam on the espresso.