Espresso drinks are enjoyed the world over and there are an
enormous number of different types and makes of espresso
machines available. However they all use a similar process
to extract the delicious coffee oils into the final
beverage.
It is the quality and formation of the 'crema' that
reflects the quality of the espresso beverage. The best
indication of good espresso is the crema.
The 'crema' traps and holds the finest coffee oils and
aromas that in other brewing processes are lost to the
atmosphere. The crema should form as a thick, golden-brown,
marbled foam across the whole surface of the espresso cup
and cling to the sides.
In addition to the quality of the crema, the appearance of
the flow or pour of the espresso from the spout of the
espresso machine also signals quality. Initially, you
should see a thick, almost viscous, dark, honey coloured
flow that gently lightens as the extraction proceeds. The
flow should form a continuous, flickering stream, similar
to the tail of a mouse, up to the point of shut-off 20 or
so seconds later.
It is important to look out for the signs of under or over
extraction in the espresso process and take corrective
action accordingly.
Over-extraction is signified by a slow, broken trickle with
a dark brown (burnt) crema. This means that the water and
coffee were in contact for too long. This occurs if the
coffee grind is too fine, effectively blocking the filter,
or by using too much coffee in the filter basket. The
coffee will scorch in the basket and the espresso will
taste bitter and burnt.
Over-extraction can also occur if the brew cycle is too
long and harsh coffee acids and tannins are extracted by
too much water passing through the coffee. The appearance
of white marks or streaks appearing towards the end of the
pour is an indication of the brew cycle being too long.
Under-extraction is signalled by a rapid, bubbling flow
from the spout and a thin, broken crema. This can be a
result of using a coffee grind that is too coarse, by not
using sufficient coffee or from tamping too lightly. All
result in the hot water passing through the coffee too fast
so it is unable to extract the desired coffee solubles and
oils. The result is a thin, insipid sour brew of espresso.
Under-extraction can also be a result of the water
temperature being too low.
By carefully watching out for these symptoms the espresso
machine operator or barista can take corrective action to
ensure delicious espresso drinks are always available.
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For more information about coffee and coffee making
equipment visit http://www.cafebar.co.uk and view our
Coffee School Section
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