Espresso coffee is several things all at once. It is a unique method of coffee brewing in which hot water is forced under pressure through tightly packed coffee, a cup a t the time. In a larger sense, it is an entire approach to coffee cuisine, involving not only roast and brewing method, but grind and grinder and a technique of heating milk for a creamy cappuccino. And in the largest sense of all, it creates an atmosphere or mystique where the espresso brewing machine is the spiritual heart and aesthetic centrepiece of the European-style cafè.
In normal brewing processes the water seeps by gravity down through ground coffee loosely laid over a filter, whilst in the espresso process the water is forced under pressure through very finely ground coffee packed tightly over the filter. A fast, yet thorough brewing makes the best coffee. If hot water and ground coffee stay in contact too long the natural aroma and flavour will evaporate and it will be lost.
Hence the superiority of the espresso system. The pressurized water makes almost instant contact with every grain of ground coffee, and just as instantly begins dribbling out into the cup. Another advantage to the cafè espresso system is freshness. Every cup is instantly brewed in front of you, a moment before you drink it.
Cappuccino lovers also soon discovered that steamed, foamed milk both tastes and looks better than milk heated in the ordinary way, this becoming an important part of the success of espresso cuisine. The white head of foam is decorative, can be garnished with a dash of cocoa or cinnamon, prevents the skin from forming on the surface of the milk, and insulates the hot coffee underneath it.
The heart of these marvellous espresso coffee machines is a water tank and heating element. Water is quickly heated to almost boiling inside the tank. A space is left at the top of the tank, where steam gathers. When a valve is opened below the water line, the pressure of the steam trapped at the top of the tank forces hot water out the valve and down through the coffee delivering a rich, creamy cup full of flavour and with that perfect aroma that made European cafes famous world wide.