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.

Disclaimer: 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.

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.

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.

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.

• Testing a Grind
• Grinder cleaning and maintenance

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

• Checking boiler level, temperature, and pressure.

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 will occur:

• 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.

SUPPLY UNIT

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 adjustment screw.

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: 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: