The secret to developing the flavour and aroma of coffee
is found in the roasting of the coffee beans. The length
of time and temperature of the roast is critical, to develop
a quality cup of coffee. Coffee roasting is an art. If
coffee roasting is too short to bring out the oils, the
coffee will have a nutty flavour and lack consistency.
Darker roasts, which produce stronger coffee, are achieved
through longer roasting periods or by utilizing higher
temperatures
The
basic roasting principals are outlined below. Specific
roasting equipment offered by various manufacturers
will provide slightly altered technical applications.
Green
coffee beans are introduced into a closed roaster. Inside,
the beans are subjected to hot air for a specific period
of time and temperature, depending on the "roast
style" desired.
The
heat inside the roaster increases at a gradual rate
and peaks at approximately 200o to 260o celsius. At
this point, rapid chemical changes occur (termed "pyrolysis"),
resulting in aroma, taste and appearance characteristics.
The
amount of time the beans are in contact with this heat
will typically vary from 3 to 20 minutes. At a constant
temperature, the coffee beans become darker the longer
they are roasted. Darker roasts can also be achieved
by roasting at higher temperatures.
Once
the intended roast colour is attained, the roasting
process is abruptly ended by cooling the beans with
water (termed "quenching") and/or cool air.
In
order to assure consistent physical levels of roasting
are achieved, commercial roasters commonly utilize an
Agtron colorimeter which provides an accurate, rapid,
numeric measure of colour.
As
a result of roasting, green coffee will experience a
weight loss of 14% - 23%, depending on the degree of
roasting. The International Coffee Organization standard
states that 100kg of roasted coffee is equivalent to
116kg of green coffee.
AFTER-DINNER ROAST - A coffee that has been roasted
to a dark, but less than very dark brown colour. It
has a somewhat oily surface. An after-dinner roast lends
a bittersweet, tangy flavour to the beans.
CINNAMON
ROAST - Light cinnamon brown colour; pronounced
nut-like flavour and the highest point of coffee acidity.
This is a light roast.
AMERICAN
ROAST - Even chestnut brown; has a pronounced caramel-like
flavour, with no trace of dark roast flavour. This is
a medium roast.
CITY
ROAST - Dark brown with no traces of oil on the
surface; full development of coffee flavour (caramel
to chocolate-like with some hints of dark roast flavour)
and some loss of coffee acidity. The "Full City
Roast" is slightly darker with more tang.
VIENNA
ROAST - Dark brown with small amounts of oil on
the bean's surface; noticeable dark roast flavour.
FRENCH
ROAST - Very dark brown with large amounts of oil
on the bean's surface; a bitter taste and pungent aromatics
dominate flavour. (Also known as New Orleans or Continental
Roast.) This is a dark roast.
ITALIAN
ROAST - Black colour with large amounts of oil on
the bean's surface; pronounced burnt flavour that is
pungent (strong) and bitter.
ESPRESSO
ROAST - Designed for espresso machines, it is a
dark roast similar to a Full City Roast.
