Tuesday, May 18, 2010
This simple cup of cappuccino never fails to amaze us. From the different layers of colors, the complex coffee fragrance and even the way milk is frothed.
The other day, dad tried frothing a bottle of fresh milk and it came out completely flat. The first thought was the bottle of milk went bad. That tasted perfect. Creamy and cold, yum!! Only then did dad remember that full fat foams, though fuller in texture and flavor, are much much more difficult to make. Of course, he never had any problems using UHT full fat milk to froth before, since those are never very creamy.
You might be surprised to hear that the scorching hot steam coming out of the steam nozzle on an espresso machine is not an essential ingredient of the cappuccino milk foam. In fact, one can argue that the steam is detrimental to the formation and maintenance of the milk foam. The foam is formed by splashing milk and air together and the steam is just an agent in the process. The resulting water vapor or the condensed water are bad because the foam bubble wall becomes runny and prone to collapse if it is hot and has high water content. Hence frothing is best done with a lot of ice cold milk and the nozzle is only placed just below the milk surface.
Given that the hot steam is not an essential part of frothing but splashing the milk is, there are devices that splash milk mechanically, like the Nespresso Aeroccino. Since high temperature is bad for holding the bubbles, you can even have cold milk foam for cold drinks.
For those of you who want to know why full fat milk is tough to froth into foam, you might want to look up whey proteins, which are essential in stabilizing milk foams and ice crystals in ice creams. It also plays an essential part in body building.