MAHLKÖNIG GMBH & CO.KG
MARKETING&COMMUNICATIONS
TILSITER ST. 142
D-22047 HAMBURG
TEL: +49 40 696940-0
FAX: +49 40 696940-88
Grinding Coffee Correctly: The
Basics
What matters when grinding coffee
MAHLKÖNIG WHITEPAPER 1/2011
Grinding Coffee Correctly: The Basics
Summary
The quality of coffee drinks depends primarily on the quality of the
raw materials, i.e. coffee beans. Secondly, the correct grinding
and preparation also play an important role.
Grinding the roasted coffee beans is the basic requirement for
preparing coffee drinks; it increases the surface area of the beans
that come into contact with water. In every roasted coffee bean,
there are approximately 1,000 different aromas and flavours.
Through the milling of the grinding process, the cell structure in
the coffee bean is broken up. Flavour, colour and aromatic
substances are released and can be dissolved more easily and
quickly upon contact with water.
Depending on the grind - coarse or very fine - the surface of the
coffee changes, and many different flavours become soluble.
Volatile aromas are immediately released; they combine with
oxygen and provide the intense coffee smell during grinding.
Studies have shown that ground coffee loses approximately 60%
of its aroma after 15 minutes. Therefore, coffee should be freshly
ground whenever possible.
MAHLKÖNIG WHITEPAPER 1/2011
Grinding Coffee Correctly: The Basics
Contents
1. The roasted coffee bean and its ingredients
2. Why grind coffee?
3. Different grinders
4. The perfect grind for every preparation
5. Goodbye, Aroma?
6. Sources and literature
MAHLKÖNIG WHITEPAPER 1/2011
1. The roasted coffee bean and its ingredients
The raw, unprocessed coffee bean contains various carbohydrates, lipids,
proteins, acids, minerals, and water. However, in its "raw" form coffee is
undrinkable. The basic substances to which an enjoyable drink is created
from green coffee are indeed already present in green coffee. However, it is
the roasting process that ensures that these are released. A coffee bean has
more than a million cells. During the roasting process, more than 1,000
different volatile compounds, called flavours, arise in these cells. Of these,
about 850 are known to us.
A coffee bean consists of approximately 30% - 40% carbohydrates, mainly
water-insoluble and soluble complex sugars (polysaccharides). During the
roasting process, the carbohydrates change drastically. The sugars are
almost completely broken down and the water-insoluble complex sugars
make up the coffee grounds later.
Green coffee contains between 10% and 13% fat (lipids), which is
responsible for the coffee oils. As the lipids are practically insoluble in water,
they are only available in very small quantities in the finished coffee drink.
Although acids make up only about 5% of the green coffee beans, they play
an important role in the taste. 80 of the different acids are known to us. The
main component is the chlorogenic acid. During roasting, up to two-thirds of
the acids are removed.
About 11% protein is found in green coffee beans, but the heat during
roasting reduces this amount significantly.
As do many species of plants, the fruits of the coffee tree contain alkaloids,
which are nitrogen-containing compounds. The most well-known, with a
proportion of 0.8% - 2.5% is caffeine. Aside from caffeine, green coffee
beans also contain trigonelline, nicotinic acid, or theobromine. Although the
MAHLKÖNIG WHITEPAPER 1/2011
roasting process barely affects the caffeine content, trigonelline degrades to
75% and creates the vitamin niacin (nicotinic acid).
The mineral content varies widely, depending on coffee variety, soil and
growing conditions. The average share is approximately 4%. Coffee mainly
contains calcium, magnesium, and phosphorus. All other minerals are also
present in trace amounts. 90% of the contained minerals are soluble in water
and become the coffee beverage.
Coffee is a very richly aromatic beverage. Of the approximately 1,000
flavours not all of them are known today. Many of them are created only
during the roasting process by heating carbohydrates with proteins in the socalled Maillard reaction.
Aside from creating flavours, the roasting process produces a dry and
crumbly texture in the beans. This facilitates grinding (milling) of the coffee
and heightens the extraction efficiency. The duration of the roasting process
influences the hardness of the beans and therefore, ultimately, the grind. The
longer the roasting process, the darker and more brittle the coffee bean
becomes, and the more easily it can be ground. After short, light roasts, the
beans are tougher due to the higher moisture content - more energy is
needed to grind them.
MAHLKÖNIG WHITEPAPER 1/2011
2. Why grind coffee?
The volatile flavours are trapped in the cells like in a vault. The cells can only
be broken up by crushing the bean through grinding. The flavours can be
released with the help of hot water during the brewing process, so that they
arrive in our cups. The milling during grinding has another effect. The whole
coffee bean in its compact, oval form offers little surface area and therefore
little opportunity for the water to extract the content and flavour of the bean.
During grinding, according to the grinding setting, the surface area of the
coffee increases exponentially. It also increases the attack surface for the
water, thus enabling the quicker transfer of the soluble components in the
water and eventually in the cup in comparison: A coffee bean being milled for
filtered coffee is broken into about 500-800 particles. In the espresso grind, it
is broken into around 3,500 particles. The very fine grind for Turkish coffee
contains 30,000 small pieces from one bean.
The grind, i.e. the number and size of the particles into which a bean has
been ground, determines the extraction time. This is the description of the
time that the water takes to release the desired contents from the ground
particles.
Depending on the preparation method of the coffee, the grind must be
correspondingly selected in order to achieve the desired result in the cup.
MAHLKÖNIG WHITEPAPER 1/2011
3. Different grinders
Probably the oldest method to crush coffee beans is the grinding in a mortar,
as it is often practiced today as part of the Ethiopian coffee ceremony.
Uniformly sized crushing and particle sizes are not possible using this type of
"grinding".
At home, one still finds grinders with a hand crank or a fly cutter. Both
versions are relatively cheap, but the coffee is neither particularly finely nor
particularly homogenously ground. However, private households are
depending more and more on high-quality grinders for home use that
incorporate the technology of professional grinders.
These professional mills mainly operate using two different types of grinders the burr grinding mill or the disc grinding mill.
A grinder consists of several components: the grinding chamber, the motor
and the grinding discs or burrs.
Burr grinders are made up of an outer, rigid grinding ring and a moveable
inner conical grinding cone. The adjustment of the grind is changed by the
setting on the outer ring. The inner grinding cone is driven by a motor and
grinds the beans at 400-900 revolutions per minute. Thanks to the power of
gravity, the ground coffee is moved downward, out of the grinder.
Burr grinders are very commonly found in restaurant espresso grinders,
which use a dosage system. An advantage of this grinding style is the
reduced heating of the ground material. As a result of the larger grinding
surface, these grinders mostly use low engine speeds. The grinding capacity
of burr grinders depends heavily on the level in the bean container, which
can negatively affect the dosing accuracy in Grind-On-Demand settings.
MAHLKÖNIG WHITEPAPER 1/2011
The slow engine speed and the large grinding surface in the grinder require a
high torque (Nm Newton meters) from the motor. Therefore, the conic burr
grinders are usually built to be much larger.
Grinders with flat grinding discs can be found in many professional espresso
grinders nowadays and also built-in grinders in most bean-to-cup coffee
makers. The serrated grinding discs lie flat on top of each other; one is
stationary, the other is connected to the motor shaft. Regulating the distance
of the two discs in relation to each other allows the grind to be set very finely
and set to be infinitely adjustable. The powerful motor provides fast rotational
speeds of up to approximately 1,600 revolutions per minute, and, therefore,
extremely short grinding times of a few seconds.
This high engine speed (revolutions per minute) can lead to higher heating of
the grinder's mechanism, which is, however, offset by the smaller grinding
surface.
Grinders with flat grinding discs are also built more compactly due to the
lower torque (Nm) pulling motors.
4. The perfect grind for every preparation
For each different coffee preparation method, for example, the manual
infusion with a filter, the preparation with the Carlsbad or the French press,
the filter machine, the fully automatic coffee maker, or the sieve coffee
maker, a special grind of coffee is needed to extract the optimum aroma and
acidity from the roasted beans. The surface area of the ground material must
be larger or smaller according to the amount of water used and the contact
time with the water, which is to say that the coffee must be ground coarser or
finer.
MAHLKÖNIG WHITEPAPER 1/2011
For manual preparation with manual infusion, the French press, or the
Carlsbad pot, the contact time with the brewing water usually takes several
minutes. The roasted coffee should be ground more coarsely for this
preparation type (average particle size of 0.6mm to 1mm - like coarse sugar).
If the coffee is ground too fine for hand infusion, the coffee will be overextracted and undesirable bitter compounds and acids will be released.
With the machine filtering, the water runs frequently and in several portions pulse brewing - through the ground coffee in the filter. For this process, the
grind should be medium fine (average particle size approx. 0.4 mm). If the
grind is too coarse, the water runs too quickly through the ground coffee and
is not given enough time to extract the desirable flavours. However, if the
grounds are too fine, the water accumulates in the filter and cannot run or
can only run through very slowly; the coffee is over-extracted and becomes
too bitter.
When preparing coffee with a super-automatic or a semi-automatic espresso
machine, the water is pressed through the ground coffee with several bars
above atmospheric pressure (bar); the contact time should not be longer than
25-30 seconds. In order to make enough flavours soluble in this very short
extraction phase, the beans must be ground very finely (average particle size
approx. 0.2 mm - small pieces are barely still noticeable).
The grind must be finer still for the preparation of Turkish coffee (Mocca,
Ibrik, Cezve) because in this case the almost dust-fine ground coffee is
directly added into the water (average particle size below 0.1 mm - fine flour no pieces noticeable).
MAHLKÖNIG WHITEPAPER 1/2011
5. Goodbye, Aroma?
Coffee in its roasted and ground state is a fragile commodity. The ingredients
only become solvent by breaking open the cells. However, the cells contain a
large portion of volatile aromas, which react with oxygen in the air (oxidation).
One can assume that approximately 15 minutes after grinding over half of the
aromas have been oxidised and are therefore lost for the preparation.
Therefore, coffee should always be ground freshly right before preparation, if
possible. This is the only way to assure the same quality in each and every
cup.
Pre-ground coffee for the retail is vacuum-packed to minimise this loss of
aroma. So that the coffee grounds do not lose their last bit of flavour in the
packaging, the oxygen is removed with a vacuum and the package is then
sealed shut. Opened packages of ground coffee should therefore be
consumed as quickly as possible and should be stored in a cool, dry, and
dark area. Do not transfer into other containers and always reseal tightly.
Where appropriate, the coffee bag should be placed in an airtight container.
MAHLKÖNIG WHITEPAPER 1/2011
Sources and literature
Gerhard A. Jansen, Roasting Coffee, Süddeutsche Verlag, 2006
Brochure: Coffee Competence Compendium, Probat-Works from Gimborn
machine factory GmbH
Dr. Steffen Schwarz / Martin Kienreich, FAQ Coffee, coffee media & event,
2008
German Coffee Association (Ed.), Coffee Knowledge: From the farm to the
final product, 2004
MAHLKÖNIG WHITEPAPER 1/2011
More MAHLKÖNIG Whitepapers:
1/2011 Grinding coffee correctly: the basics
2/2011 Grinding coffee correctly: fresh or stockpile grinding?
3/2011 Grinding coffee correctly: Espresso
4/2011 Grinding coffee correctly: Filter coffee and French press
5/2011 Grinding coffee correctly: Grinder cleaning and maintenance
6/2011 Grinding coffee correctly: Grinding in super-automatic coffee machines.
Contact
MAHLKÖNIG GMBH & CO.KG
MARKETING&COMMUNICATIONS
TILSITER STR. 142, D-22047 HAMBURG
TEL: +49 40 696940-0, FAX: +49 40 696940-88
E-MAIL: [email protected],
WEB: www.mahlkoenig.de
For over 80 years, MAHLKÖNIG has been the world's leading brand in the field of quality grinders for
professional users. The MAHLKÖNIG logo stands for innovative and quality leadership. The development of
grinders for an optimal grinding of all sorts of roasted coffee is the focus point of our work. Therefore, almost 90%
of the MAHLKÖNIG products are used in the coffee grinding field. The goal is to carefully and homogeneously
grind the coffee without loss of flavour.
MAHLKÖNIG now has a national and international network of its own branch offices and works with over 150
distributors and service partners to support over 400,000 MAHLKÖNIG grinders worldwide. The MAHLKÖNIG
know-how is used everywhere, daily.
MAHLKÖNIG WHITEPAPER 1/2011