This type was the first kind espresso machine that ever
received any real popularity in the American mainstream.
Here's how it works: water that has been poured into
a reservoir is heated to boiling. This same water is
used both to steam milk and brew the espresso. This
method gets the water pressure up to about 1 bar (although,
the preferred pressure at which espresso is brewed is
about 8 bar).
Many folks like using an electric steam espresso machine
in order to brew a coffee just a bit stronger than drip
coffee. However, given the advent of the next type of
machine, boiler machines are now of out of step with
mainstream espresso connoisseurs. (See image 1)
Advantages
--These machiens are relatively inexpensive; machines
can start at $30.00.
--The units usually include a carafe for espresso collection.
--They feature simple to use electronics; usually these
machines incorporate just a few switches and a dial.
--Not an espresso fan, but want strong coffee? This
unit can do that.
Disadvantages
--Only very low pressure can be achieved, which makes
the production of crema unlikely. The espresso made
from these units is widely considered to be sub-par.
--Water reservoir takes several minutes to heat up
and usually does not hold much water.
