The following is a brief, technical explanation on how the grinder-dispenser
and espresso machine work. Some basic
troubleshooting is also illustrated. This information concerns the average
professional equipment ONLY. Home espresso gear differs, sometimes
significantly, from the specifications below, and this information is not
at all intended to be applied to such equipment, although the basic principles
may be the same.
All specifications, tips and troubleshooting provided below are for informational
purpose only. Before attempting any repairs or fine-tuning to equipment
on your own, carefully consult all owner's manuals and your local supplier
or distributor. Remember that any adjustments to your equipment, even if
small and apparently insignificant, may not only invalidate warranties
and service contracts with the manufacturer, but may also represent a potential
hazard to you, your employees, and your customers. Therefore, proceed at
your own risk.
Other less common type of equipment (such as older piston-type espresso
machines or newer, superautomatic systems) are not discussed here. However,
most of the information below apply to these units as well as to the more
common, semi-automatic or automatic pump-driven machines which represent
the great majority of the equipment in use today by Food Service operators
around the World.
Grinder - Dispenser
Please read the Disclaimer on Top
of this Page before reading on.
Experts agree that good coffee depends on the freshness of the grind,
and grinding beans just before use is the only way to keep all of the aromas
intact. The grinder-dispenser produces freshly-ground coffee and dispenses
exactly the right amount for each cup of espresso.
Technical data: Professional grinder-dispensers on the market
today are single-phase, either 110V or 220V. A single-phase plug has two
prongs and a ground pin.
STANDARD GRINDER-DISPENSER COMPONENTS
Bean Hopper: a see-through container on top of the grinder which
holds the beans and feeds them to the grinding blades. Very often, it includes
a magnet that hangs just above the feeder to the grinding blades. The magnet
is designed to attract any ferrous objects (such as nails, staples, screws,
etc) mixed in the coffee beans, which could otherwise cause permanent damage
to the blades and the motor.
Flat Grinding Blades
|Dispenser: a see-through container which
collects the ground coffee. A lever connected to the feed system
is used to dispense a single cup measure of coffee. This measure can normally
be increased or reduced by turning the knurled knob on the outside or the
inside of the dispenser. Tip: do
not leave too much ground coffee in the dispenser; it should never be more
than three-quarters full. Also, no coffee should be left in the dispenser
at the end of the day, as any unused ground coffee will very quickly lose
its aroma and absorb odors and humidity. The appropriate measure of
ground coffee per cup is approximately 0.2 oz (6.5 - 7 grams). To check
the accuracy of the measure, dispense five measures, then weigh the total
and divide by five to get an average measure. If the average is not close
to 0.2 oz., the dispenser should be readjusted.
Grinding blades: the most important component
of the grinder, because a good cup of espresso depends on their proper
use. There are two toothed grinding blades which rotate at high speed to
crush and grind the coffee beans evenly. Two types of grinding blades,
flat and conical, are used in today's modern grinders.
- Flat grinding blades: two identical, tempered steel, toothed
discs of the same size that work in opposition to each other. One is fixed
to the motor shaft, the other to the threaded collar. The motor shaft rotates
at very high speed (900 to 1400 rpm), which means that prolonged use can
cause overheating of the metal, and this may alter the flavor of the coffee.
- Conical grinding blades: two blades of different shape. The
first is a truncated cone-shaped blade which is fitted to the motor shaft.
The second is cylindrical on the outside, but on the inside it is the reversed
shape of the flat blade. This blade is fitted to the threaded collar. The
speed of the cone-shaped blade is much slower than that of the flat blades
described above (400 to 600 rpm).
To regulate the fineness of the grind, simply
tighten or loosen the threaded adjustment collar under the container.
Some models have a knurled adjustment knob instead, which moves
the grinding blades closer together or farther apart to produce finer or
coarser ground coffee.
To determine the condition of the grinding blades, take a pinch of ground
coffee and check to see if the grain size is uniform. If there are larger
grains mixed with a fine powder that stains the hands, the blades are worn
and should be replaced. If used correctly, a set of standard flat blades
will grind approximately 880 lbs (400 kg) of coffee, a set of conical blades
twice that amount. Therefore, care should be taken in checking the average
daily usage of coffee beans to establish the frequency of blade replacement.
This operation can be performed by the supplier or by the operator, if
manuals are provided.
|3.3 lbs (1.5 kg)
||Once a year
|6.6 lbs (3.0 kg)
||Every 6 months
|13.2 lbs (6.0 kg)
||Every 3 months
Wiping the Filter
Tamper: the last component to be used before operating the espresso
machine. It is used to pack down the ground coffee in the filter basket
to produce a uniformly flat surface and ensure a thorough and even extraction
of the flavors and aromas by the pressurized water. A fixed or spring-loaded
tamper is normally mounted on the grinder. Stand-alone models are also
available, made either of plastic or metal. Tip:
After tamping down the coffee, wipe the rim of the filter basket with the
palm of your hand before inserting the basket into the espresso machine
dispenser. This will stop grains of coffee from falling into the cup, and
increase the life of the gaskets.
TROUBLESHOOTING a Grinder-Dispenser
Please read the Disclaimer on Top
of this Page before reading on.
Espresso coffee is prepared by a special extraction method which produces
a very concentrated, strong coffee is a short amount of time. Softened
water at a temperature of 90-95 Degrees C is forced through finely ground
and specially roasted coffee at high pressure (about 9 atmospheres). The
contact between the water and the coffee varies from 25 to 35 seconds.
The amount of ground coffee per cup varies from 6.5 to 7 grams. The coffee
beans must be roasted to a medium to dark colour, and then finely ground.
This produces a cup of espresso with a volume of between 10 and 20 millilitres.
There are four factors which ensure a genuine Italian-style cup of espresso:
- The infusion time
- The temperature of the water
- The pressure
- The coffee blend.
HOW THE MACHINE WORKS
In auto-fill machines the water is drawn directly from the water supply,
and a heat-exchanger brings it up to the right temperature for making espresso.
Before the heat-exchanger performs its functions, pressure is generated
by a positive-displacement pump, which can be adjusted to achieve a pressure
of approximately 132 pounds per square inch (9 atm).
"Infusion time" occurs when heated water is forced under pressure
to pass through the grind in order to extract the soluble flavor and aroma
substances from the coffee. Under most makes and models of professional
machines, this takes about 5 seconds.
First, water under low pressure is released into the space between the
diffuser and the filter holder. When this space is full, water is forced
through the tamped coffee by the positive displacement vacuum pump at the
above pressure. When the brew starts pouring from the spout into the cup,
"dispensing time" begins.
STANDARD ESPRESSO MACHINE COMPONENTS
Boiler: a cylindrical reservoir that contains
water and steam, which are heated to the temperature required for making
espresso. The heat exchanger is a smaller cylinder or cartridge
built inside the boiler chamber, through which cold water is drawn from
the main water supply. This cold water is therefore heated by the hot water
in the boiler. Both heat exchanger and boiler are generally made of copper.
A good cup of espresso depends on the correct ratio of water and steam
in the boiler.
|Level gauge: a glass tube with both top
and bottom ends fitted into the boiler. The tube indicates the exact amount
of water in the boiler, and must be monitored regularly to assure correct
level of water in the boiler chamber. In most modern espresso machines,
such level is automatically regulated by auto-fill mechanisms through the
use of a probe inside the boiler.
IMPORTANT NOTE: The level of
water in the boiler greatly affects the quality of the brew. If the level
is too low, water will be overheated, resulting in "over-brewed"
coffee. If the water level is too high, on the other hand, the following
- Underheating of the water leading to "under-brewed" espresso;
- Insufficient volume of steam in the boiler, leading to reduced performance
when operating the steamer.
Pressure regulator (pressure-stat): a device for regulating the
pressure in the boiler and keeping it within predetermined settings. The
pressure-stat powers the heating element inside the boiler on and off as
necessary. Its settings can be adjusted by turning the appropriate screw.
Pressure gauges: Normally two instruments which measure and indicate
both: a) the pressure in the boiler and, b) the pressure generated by the
positive displacement pump.
Safety valve: a calibrated and sealed valve which discharges
steam from the boiler whenever steam pressure exceeds a pre-set limit.
Positive Displacement Vacuum Pump: the unit which generates the
pressure (approximately 9 atm or 132 psi) required to make espresso. It
can be built inside the machine body or mounted under the counter. Pump
pressure can normally be adjusted by tightening or loosening the appropriate
To check the pump pressure,
leave the full filter basket in place after making a cup of espresso (or
replace the filter basket with a "blank" filter, one with no
holes) and let the machine run water through it. The pressure level gauge
should read approximately 132 psi. (9 atm.). If the pressure is too high
or too low, turn the adjustment screw on the pump clockwise to increase
it, counter-clockwise to decrease it.
Water and Steam Spouts
Soaking Filter Holders
Water and steam spouts: for heating and preparing drinks. Tip:
Never draw hot water from the boiler to prepare drinks such as teas. The
water is not fresh and may be contaminated with backflushed milk residues
from the steam wands.
Filters: round metal strainer baskets which
hold pre-measured amounts of ground coffee (1 and 2-cup models exist),
and are held into the filter holders. Coffee liquid produced by pressurized
water passes through the holes in the filters and into the cup. Both filters
and their holders will last much longer if you remember, at the end of
each day, to soak them in water overnight. Never use soap to clean
these parts. To check them for scale,
hold them against a source of light. If the holes are badly plugged or
not of uniform size, replace the baskets with new ones.
Diffusers: mesh screens that ensure the
even distribution of hot water over the tamped coffee in the filter. They
should be changed or cleaned regularly. A typical symptom of worn out or
partially blocked diffusers is hollows left in the coffee grounds in the
filter holder after extraction.
Gaskets: cylindrical seals made of Viton®
(Registered Trademark of DuPont Dow Elastomers), which maintain a watertight
seal between the filter and the dispenser unit.
Water softener: a unit containing cationic
resins which neutralize substances in the water that cause scaly deposits.
The result is purified, softened water. The unit is situated behind the
displacement pump, between water line and espresso machine. It
needs to be replenished on a regular basis with ordinary coarse salt.,
which dissolves in the unit and "regenerates" the resins, according
to the following schedule:
|3.3 lbs (1.5 kg)
||Once a month
|6.6 lbs (3.0 kg)
||Every 2 weeks
|13.2 lbs (6.0 kg)
||Once a week
TROUBLESHOOTING an Espresso Machine