extract espresso properly it is essential to use an espresso burr
grinder and to grind per order. The two major types
of burrs used are flat and conical. Conical burr coffee grinders
are desirable because they increase the surface area of
each particle and the amount of flavor that can be extracted
from the coffee. Since a conical burr grinder has longer cutting
edges, the burrs can rotate at lower speeds, which reduces
the heat created. Flat burrs should be replaced after
600 pounds of coffee have been ground and conical burrs should
be replaced after 2000 pounds of coffee have been ground.
Coffee Beans: Grinding Guide
Coffee is freshest immediately after it
is ground. After grinding coffee beans, the volatile oils that were
previously protected inside the bean are exposed to the
air which oxidizes and stales the coffee. This effect
occurs immediately after coffee grinding so it is important to
tamp and extract the espresso as quickly as possible.
The coffee grinder should be activated for 15-20 seconds every
time a shot is desired so that only freshly ground coffee
is used. Instead of two pulls on the doser, the barista
should pull several times until the entire basket is filled
with ground coffee. See the section on
espresso tamping for additional instructions.
Espresso coffee should be ground
to a size in which the extraction process
takes 23-28 seconds. It is important to only adjust
the grind and not the pressure one tamps with to control the
flow rate. In addition to particle size, the humidity
plays a dramatic role on extraction time. Since coffee
is hydroscopic, it absorbs moisture from the air causing a
tighter pack and longer extraction time. Thus, the
grind setting must be changed slightly throughout the day as
the barista perceives changes in extraction time.