beans are best fresh. They must be roasted in order to be
used, a process that normally takes place before the beans
are sold. This roasting starts a degradation process,
whereby the oils and flavor compounds break down and
generally become bitter and less flavorful. Surface area
is a large part of the degradation, so ground coffee
degrades considerably faster than whole-bean coffee.
The flavors in coffee are
extracted by hot water, and there are a number of ways by
which to extract these flavors. The coffee must be ground
for all of these methods -- just as the increased surface
area contributes to faster degradation, it also allows the
rapid extraction of flavor by water. There are two basic
methods by which this is done, either by allowing the
grounds to sit in hot water and steep like tea, or by
forcing hot water through the grounds. Generally some
combination of these two processes is done.
On the one extreme is the
French press. The grounds are placed into the bottom of a
vessel and hot water is poured onto them. The mixture sits
for a few minutes (A), then a mesh strainer is
pushed down onto the mass (B) and the coffee (C)
is poured off to drink.
The other extreme is
espresso. A fine grind of strong coffee is packed into a
small metal container with a hole in the bottom.
Pressurized water is forced through the grounds, where it
extracts a strong flavor, then falls into the pot below.
Although some sources say that espresso is made with pressurized
steam, no espresso machine actually works this way. The
pressure is usually driven by some type of electric pump,
but hand-operated pistons are also available.
In America, the most
common brewing method is the drip method, which is halfway
between these two. The grounds are placed in a basket with
a non-reactive liner of paper or sometimes gold, with a
small hole in the bottom. Hot water is poured over the
grounds, where it soaks the grounds and steeps for a short
time while being slowly forced by gravity through the hole
into the container below where it is kept warm (or at
least insulated) while the brewing process finishes.
In Italy, the most common
method of brewing coffee is in a moka-style percolator.
Water is placed in the lower section (A) and the
raw coffee grounds in the mid-section (B) with the
spout reaching below the water level level. After the top
section, initially empty, is affixed, the pot is placed on
a heat source. As the water reaches boiling point it turns
to steam and eventually creates sufficient pressure to
force all the water from the lower section up the tube at
once, through the grounds — which are held in place by a
metal filter above and below — and through a second tube
until it hits the lid of the pot and is collected in the
upper section (C), producing a strong, concentrated
coffee. Gaskets and safety valves to ensure a tightly
closed unit allow for pressure to safely build up in the
lower section and provide a necessary security release if
this pressure gets too high.
There are many factors in
the final result. First is the roast and quality of the
coffee beans. Freshly ground, newly roasted beans will
always give a better cup of coffee than pre-ground, older
beans. Clean fresh water is necessary, and the temperature
of the water will have some bearing on the result. Cooler
water will not extract flavors as efficiently as hot
water, but boiling water can be a little too good with a
very dark roast. Lastly, the coarseness of the grind and
the ratio of grounds to water are also important, and vary
according to the brewing method used.
A good rule of thumb for
beginning brewers is to use the simple drip method. Use 2
Tablespoons of finely ground coffee for every 6-7 oz of
fresh water. Bring the water just to a boil, then pour
slowly over the grounds, stirring gently as you do.
Stirring will result in the grounds retaining some extra
water, but do not try to squeeze the water out. When it
stops dripping, the coffee is ready to drink.