Whatever type of coffee or coffee brewing
equipment used the objective is usually the same.
That is, to extract and put into solution, the coffee oils and
the soluble (and semi-soluble compounds) that are formed when the
coffee bean is roasted.
It is possible to extract as much as 30% of the coffee beans
mass into solution, by grinding the bean into a powder and steeping
in hot water. These soluble compounds however dissolve at different
rates and not all of them are beneficial to the coffee taste.
Tannin and caffeine in higher concentrations for example can cause
the final beverage to taste sour.
18%-22% is the optimum extraction rate for good coffee.
Under Extraction occurs when the brewing time is
too short and not enough coffee soluble are extracted into
solution. This can occur if the water is not hot enough or if the
water passes through the ground coffee too quickly. An
insipid, thin brew lacking in body and flavour will result.
The opposite, Over Extraction occurs when the
water is in contact with the ground coffee for too long and too
much of the coffee soluble are extracted than is desirable. A harsh
tasting bitter brew will result.
Freshness – Coffee is best enjoyed as soon as it
has been brewed. Oxygen in the atmosphere causes the taste to
rapidly deteriorate and the beverage loses its aromatic oils and
may soon become sour, flat and lifeless. Freshly brewed coffee
should be consumed within 30 minutes if left on a hotplate and
should never be reheated. The use of a thermos type flask can
extend this time up to an hour or so before the flavour is
impaired.
The quality of the brewed coffee beverage will depend on several
factors, all of which are important to produce the perfect cup of
coffee.
1/ Grind size of the coffee
2/ Quantity of coffee used
3/ Water quality
4/ Water temperature
5/ Contact (infusion) time
6/ Type of brewing method used
7/ Hygiene and cleaning practices
These key criteria will now be discussed in more detail.
1/ grind size
It is a general principle of any material that the smaller the
particle size the greater the surface area exposed for a measured
weight of material. This means that the finer the grind of coffee,
the greater the surface area of coffee exposed to the hot brewing
water and consequently the more extraction of coffee soluble takes
place per unit time.
Over-extraction can occur if the grind is too fine for a particular
brewing method and under-extraction can occur if the grind is too
large. The important thing here is the brewing method used, as
different methods require different infusion times and consequently
a different grind size.
The usual terms applied to coffee grind size are from the largest
particle size to the smallest the following...
coarse – medium – fine – very fine(espresso)
Clearly coffee brewed in a simple coffee pot where hot water is
merely added to the ground coffee in a pot a coarse grind should be
used as the hot water is likely to be in contact with the coffee
for a long time.
Inversely in an espresso machine the water is only in contact
with the grind for 20-25 seconds (although under pressure) so
a very fine (or espresso) grind is needed for optimum flavour
extraction to occur.
In a similar vein drip filter coffee machines require a medium to
fine grind as the filter paper restricts the flow of hot water into
the jug but even so the infusion time is quite short,
The cafetiere (or French Press) method requires a medium grind as
the coffee may infuse for a while before the customer decides to
end the infusion process by depressing the integral strainer to
trap the used grounds at the bottom of the pot.
Most coffees sold these days are marked with a description of
coffee grind size and the most suitable method of brewing.
2/ quantity of coffee used
It is imperative to use the correct amount of coffee appropriate
to the equipment used to brew it. Bear in mind that a fine ground
coffee will occupy a smaller volume for the same weight of
coffee.
Using less coffee than recommended by compensating by using a
longer brew time will not result in a standard brew but just
produce an over-extracted beverage. By the same token using more
coffee than recommended and using a quicker infusion time will just
result in an under-extracted coffee.
Approximate measures:
1 ounce of coffee to 1 pint of water
60 grams of coffee to 1 litre of water
¼ ounce of espresso grind for a typical espresso
8 grams of espresso grind for a typical espresso
1 heaped teaspoon = 2.5 grams of coffee
1 rounded tablespoon = 7.5 grams of coffee
4-5 tablespoons of coffee for 1 pint of water
3/ water quality
In a good cup of coffee approximately 98.5% of the beverage is
water.
Consequently it should come as no surprise that care must be taken
is using the best quality water for the brew at the correct
temperature.
The use of filtered water or water conditioned through a calcium
treatment unit is recommended as they remove taints and odours made
by trace elements and limescale in the water. Some water hardness
is an advantage, just not too much.
Ideally between 55-200 parts per million water hardness is
best) Too much water hardness can cause other problems such as
damage to heating elements and furring up values.
Softened water must never be used as this may contain high levels
of sodium compounds. Distilled water, although safe to drink, will
not make good coffee as it is so 'pure' that it will impart a flat
and lifeless edge to the coffee.
In addition always use fresh cold water in your coffee making
equipment to start of the brewing process.
4/ temperature
Unlike tea, boiling water should never be used in making good
coffee as the high temperature will scald the coffee and many of
the volatile compounds will be lost.
On the other hand water that is not hot enough will be unable to
extract many of the soluble flavour compounds and the bulk of
the flavour will remain in the grind.
The optimum range of water temperature common to all brewing
methods is between 93-98 degrees Celsius. Often referred to as
water just 'off' the boil.
5/ infusion time
The infusion time is the length of time that the coffee grind is
in contact with hot water to produce the final beverage. Common
sense would suggest that the coarser the grind the longer infusion
time is required for efficient extraction of the coffee
soluble.
In practice however the infusion time is controlled by the
particular brewing equipment used or by the end user as in the case
with a coffee pot of cafetiere.
The following infusion times given are approximately only.
Typical infusion times using the various grind sizes are:
10-25 seconds – espresso grind (very fine)
3-5 minutes – fine grind
5-8 minutes – medium grind
8-10 minutes – coarse grind
6/ Infusion method
The choice of coffee brewing equipment available these days is
vast From the humble coffee pot, the French Press, the
traditional percolator, filter machine through to commercial bulk
brew machines, traditional espresso and fully automatic bean to cup
machines and many more.
A simple cafetiere
may cost just a few pounds, whilst the latest top of the range
fully automatic coffee makers can set you back £10,000.
However, whatever the make or model and whether for domestic or
commercial use the method of coffee extraction falls into just
three simple categories.
1/ Steep and strain
2/ Filter infusion
3/ Pressure infusion
Steep and Strain – The simplest method of all. Hot
water (just off the boil) is added to coarse to medium ground
coffee in a container and the mixture left to ensure extraction
(steeping). The coffee liquor is strained off or the steeping
halted in some mechanical way prior to serving. This methods is
best suited to domestic or light commercial use.
Examples include the coffee jug, percolator, French Press,
Ibrik
Filter Infusion – Medium to fine ground coffee are
placed in a basket or container which is lined with a filter paper
or other material designed to let the hot coffee liquor slowly
filter through to a holding pot or container.
Hot water is a added from above it steeps with the coffee grinds in
the basket and falls through into the container below.
This method is suitable to both domestic and commercial use.
Examples include, drip and filter pots, pour and serve machines and
commercial bulk brewers.
Pressure Infusion – Hot water if forced under
pressure through a small compacted bed of finely ground coffee held
inside a small metal basket. This is known as the espresso process
and is generally suited to preparing individual cups of
beverage rather than a jug or container.
If you selected one particular type and grind of coffee and brewed
it through these three methods the resulting beverage would taste
different in each case.
The choice of brewing method and type of equipment used will depend
on the particular situation. At home for example a simple domestic
coffee pot, French Press, small filter drip jug or percolator will
suffice.
At a wedding function or corporate event a bulk brewer will be
needed as large quantities of coffee are required at the same time.
In a restaurant where diners are ordering coffees at different
times a traditional espresso machine would be ideally suited,
but in a cafeteria or other self service catering establishment a
fully automatic push button bean to cup machine would be the best
solution.
7/ hygiene
Last on the list, but perhaps the most important, is
coffee hygiene.
All parts of coffee brewing equipment should be regularly cleaned
and sanitised and areas that come into contact with the beverage
kept clean.
In addition the coffee beans or ground coffee should be kept fresh
in air tight containers away from damp areas and out of direct
sunlight.
Coffee beans contain a high percentage of oils and the residue
on un-cleaned equipment can quickly form black sticky tars which
can easily contaminate the next brew. All coffee brewing equipment
and surrounding areas should be washed down with hot water
containing a mild detergent and thoroughly rinsed.
To produce great tasting coffee is is crucial to have clean
brewing equipment.