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Overextraction and Underextraction
Brewing great espresso takes an understanding of what actually
winds up in the cup when coffee is exposed to water. Roughly 30%
of a roasted coffee bean is made of water soluble compounds.
20% of those compounds dissolve fairly easily, while the remaining
10% take a little more work – which is a good thing, because that
less-soluble 10% is acidic, bitter, and generally unpleasant. The goal
of all coffee making is to extract the easily dissolved oils and
compounds while leaving the rest in the grounds.
If ground coffee steeps in water too long, all the soluble
compounds will be extracted, which makes for a very bitter brew.
This is called overextraction. The opposite of overextraction is
underextraction, which occurs when coffee is not exposed to the
brew water long enough, leaving the essential flavours and aromas
locked in the grounds. Underextraction results in coffee that is weak
in taste.
Whether brewed coffee is overextracted, underextracted, or just
right depends on several factors, including the ratio of coffee to
brew water, the fineness of the grind, the brewing temperature,
and the length of time the water is in contact with the coffee.
All these factors are either directly or indirectly affected by the
barista’s technique.
Before Brewing: The Elements of Great Espresso
Before the espresso machine is even plugged in, you’ll need several
elements to produce great coffee.
Fresh Coffee Beans
Great coffee can only come from fresh coffee beans, properly
roasted. Many baristas recommend buying beans roasted no darker
than a medium roast, the colour of which appears as an even
chocolate brown. This roast preserves the natural sugars and flavour
of the bean, which sets the stage for excellent espresso. A medium
roast is the darkest a bean can be roasted without oils developing
on the surface.
Darkly roasted beans – which appear dark brown or nearly black –
look great, but the extra roasting overwhelms the more delicate
coffee flavors and caramelizes any sugars. A heavy “roasted” coffee
flavour, often bitter and sharp, will predominate with a dark roast.
To preserve the freshness of coffee beans:
Keep beans in an opaque, air-tight container and store them in a
cool, dry place. Refrigeration is not recommended, as condensation
tends to form on the beans whenever the container is opened.
Freezing can help preserve beans stored for an extended period, but
it will also impair flavour.
Continued…
TECHNIQUES OF A BARISTA