Steam-driven 
A steam-driven unit operates by forcing water through the coffee by using steam or steam pressure. The first espresso machines were steam types, produced when a common boiler was piped to four group heads so that multiple types of coffee could be made at the same time. The design is still used today in low-cost consumer machines, as it does not need to contain moving parts.
Piston-driven
The piston, or lever, driven machine was developed in 1945 by Achille Gaggia in Italy. The design generically uses lever, pumped by the operator, to pressurize hot water and send it through the coffee grinds. The act of producing a shot of espresso is colloquially termed pulling a shot, because these lever-style espresso machines required pulling a long handle to produce a shot.
There are two types of lever machines; manual piston and spring piston design. With the manual piston, the operator directly pushes the water through the grounds. In the spring piston design, the operator works to tension a spring, which then delivers the pressure for the espresso (usually 8 to 10 bar).
The piston-driven machine is the origin of the crema, which was originally thought to be an undesirable waste product but is now considered characteristic of a properly made shot of espresso.
There are two types of lever machines; manual piston and spring piston design. With the manual piston, the operator directly pushes the water through the grounds. In the spring piston design, the operator works to tension a spring, which then delivers the pressure for the espresso (usually 8 to 10 bar).
The piston-driven machine is the origin of the crema, which was originally thought to be an undesirable waste product but is now considered characteristic of a properly made shot of espresso.
Pump-driven
A refinement of the piston machine is the pump-driven machine, which has become the most popular design in commercial espresso bars. Instead of using manual force, a motor-driven pump provides the force necessary for espresso brewing. Commercial or some high-end home machines are often attached directly to the plumbing of the site; lower-end home machines have built-in water reservoirs.
Home (consumer-grade) pump espresso machines typically use a single chamber both for heating water to brewing temperature, and to boil water for steaming milk. Since the optimum temperature for brewing coffee is much less than the temperature for creating steam, the machine requires time to make the transition from one mode to the other. Commercial-grade and "semi-commercial" high end home espresso machines use the boiler chamber only for making steam. Water for brewing most commonly passes through a heat exchanger (taking some heat from the steam, without rising to the same temperature). In a few commercial espresso machines (notably La Marzocco), water for brewing is heated in a separate chamber.
Home (consumer-grade) pump espresso machines typically use a single chamber both for heating water to brewing temperature, and to boil water for steaming milk. Since the optimum temperature for brewing coffee is much less than the temperature for creating steam, the machine requires time to make the transition from one mode to the other. Commercial-grade and "semi-commercial" high end home espresso machines use the boiler chamber only for making steam. Water for brewing most commonly passes through a heat exchanger (taking some heat from the steam, without rising to the same temperature). In a few commercial espresso machines (notably La Marzocco), water for brewing is heated in a separate chamber.
0 ความคิดเห็น:
Post a Comment