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
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.
Written by Fenton Wayne - (Fenton Wayne is an independent
advisor in the coffee and vending trade where he has over 25
years experience. This article has been submitted to and
distributed by www.submityourarticle.com)