La Marzocco Espresso Machines Guideline The La Marzocco espresso coffee machines work by forcing hot water under high pressure through finely ground coffee held in a portafilter. The brewing process uses several key components to accomplish this process. Nearly every other espresso machine manufacturer uses a single boiler and heat exchanger located inside the steam boiler. Water for brewing espresso is solely dependent on the temperature of the single steam boiler and this creates inconsistent brewing and steaming conditions, thus producing inconsistent drinks. The La Marzocco espresso machine uses a unique two-boiler systems to isolate and perform operations in the best possible conditions. The rear boiler is dedicated to the steam and hot or tea water functions. The front boiler has the sole purpose of providing brewing water at the correct temperature and pressure for the coffee the barista is going to brew. These temperature and pressure parameters are adjustable independently of any other function of the espresso machine. They are also consistent though most any level of operation. HOW DOES IT WORK? Cold, filtered water enters the brewing boiler through a pump which raises the water pressure to 9 bars to allow the water to flow through the finely ground coffee. Then the water in the boiler is heated by a heating element, which is controlled by a Temperature probe connected to a CPU which control and sends power to the element when the water temperature is low and shuts off power to the element when the water is at operating temperature. This means the temperature of the coffee brewing water can be set precisely depending on the operator's taste, the roast or blend of the coffee used. When the barista puts the portafilter into the brewing group, it forms a watertight seal between the portafilter and the group gasket. When the user presses the brew switch, a solenoid valve opens and the pump generates pressure to force the hot water from the boiler through the group and the diffusion screen and screw, then into and through the ground coffee, producing the desired volume of espresso, which is brewed into heated cups or shot glasses. On automatic (AV) models, the water is measured by a flowmeter.
The flowmeter sends a signal to the microprocessor as the water flows; when the programmed amount of water is reached, the microprocessor turns off the solenoid valve and pump, releasing the pressure against the portafilter. Since the La Marzocco is built to a different principal than other espresso machines, let s look at the individual systems that make up the entire machine. 1. BOILERS There are two stainless steel boilers that work independently to provide steam and hot water or hot water for brewing espresso. The rear boiler provides steam pressure and the front boiler provides hot water for brewing espresso. The rear boiler operates partially filled and above boiling. The front boiler operates completely full and just below boiling. 2. GROUPS The groups are the actual brewing chambers that house the coffee to be brewed. The La Marzocco uses a hollow stainless steel group welded directly on the stainless steel boiler. It is critical to prevent the machine or group from cooling down. Hot water is constantly circulating in the group any time the machine is hot. This allows the group to maintain the correct brewing temperatures at all times. Once the dispense button is depressed, hot water that has been circulating though the group is released by means of a solenoid valve. Water flows from the left side of the group (as you are facing it) to the flowmeter (AV models) or to directly to the solenoid valve (EE models). The water then travels back into the group on the right side and through a tube before it is dispersed onto the fresh coffee grounds. 3. GROUP VALVES Each group has a solenoid valve mounted underneath to allow water to flow through the group. Group valves are three way valves that allow water to flow in a specific direction and that direct any back pressure to be discharged into the drain box. Each valve consists of a housing or body, which contains the valve seat, and a piston, that travels within a valve stem. The piston is spring loaded to create a seal when the valve is at rest. The valve is opened with a coil that creates a magnetic charge and draws the piston away from the valve seat and is closed with spring pressure.
4. FLOWMETER The flowmeter measures the volume of water passing through the groups. The flowmeter consists of an impeller or wheel that contains two small magnets, and a body or housing that contains a precision orifice or jet that controls the amount of water that can flow into the flowmeter. When water enters the flowmeter, the impeller spins and the magnets pass under the electromagnetic field. Each time a switch in the field closes a pulse is sent to the microprocessor to be counted. 5. AUTOFILL SYSTEM The autofill system maintains the water level in the rear or steam boiler. The autofill system consists of a sensor or probe, and a two-way solenoid valve. The sensor is a metal probe that is insulated from surrounding metal with a teflon seal and is inserted into the boiler. The microprocessor reads this post though a lead or wire. The microprocessor is programmed to detect a ground or earth signal from this sensor. If it does not, it opens the two way solenoid valve and allows water to fill the boiler. When the water level reaches the metal post the microprocessor can detect the ground or earth signal and closes the two way solenoid valve. 6. VACUUM VALVE The vacuum valve avoids the steam to escape from the boiler until sufficient steam pressure develops to lift the cone and seal the boiler. This valve prevents a false pressure reading when a machine is initially heating: as hot as it heats, the water expands. The pressure switch cannot detect the difference between air pressure or steam pressure. By allowing the air pressure that develops from the expanding water to escape, a true steam pressure can build as the machine continues to heat. This valve also reduces any possibility of contaminating the steam boiler (milk suction through the vacuum effect caused by the steam pressure decrease). 7. EXPANSION VALVE The expansion valve relieves front boiler pressure at about 12 bar. The expansion valve is located in the drain box, which is underneath the drip tray. The expansion valve consists of a valve body or housing, a valve seal and spring which are enclosed in an adjustable, and a brass barrel.
The expansion valve is adjusted by increasing or decreasing pressure on the spring by turning the brass barrel. It should begin to drip at 10-11 bar and release fully above 12 bar. 8. SAFETY RELIEF VALVE The safety relief valve relieves boiler pressure at 1.8 bar thus preventing the steam boiler from over-pressurizing. It is factory adjusted and sealed. It cannot be adjusted. 9. MOTOR PUMP The motor pump increases existing water pressure to 135psi or 9 bar. This is the optimum pressure for brewing espresso. An adjustment screw is located on the side of the pump inside the cap screw. Some pumps have accessible screws and some pumps have a cap screw that must be removed to make an adjustment. Turning the screw clockwise will increase the pump pressure and counter clockwise will decrease pressure. Make pump pressure adjustments while simultaneously brewing espresso. Check that your water supply pressure is stable before making an adjustment. A fluctuating water supply pressure will affect the final result. If your water pressure does fluctuate it is required to install a water pressure regulator or floating bypass rotating pump. 10. MAIN POWER SWITCH Power enters the machine through the power cord, which then enters a large terminal block, and then to the main power switch. The main power switch has three positions: 0 This is the off position 1 This is the fill position. It activates all systems except the heating elements. 2 This is the run position. It provides power to all systems. (JUST ON LINEA AND FB/70) 11. THERMOSTAT (ON THE LINEA AND FB/70) The thermostat controls the temperature of the front boiler. The thermostat resides in a well that isolates it from the water but allows the temperature of the water to transfer. The thermostat contains a bellows filled with a thermal fluid that expands and contracts depending on the surrounding temperature. As the water heats in the coffee boiler it causes the fluid in the bellows to expand, which drives a piston up. When the piston rises, it eventually activates a switch, which turns off the heating elements. As the water cools the piston will fall and allow the switch to turn on again and repeat the heating cycle.
The thermostat contains an adjustment screw that adjusts the distance the piston must travel to activate the switch, thus adjusting the temperature. To increase temperature turn the screw clockwise; to decrease turn counterclockwise. Each 1/4 turn of the adjustment screw represents approximately 2 degree Celsius temperature change. 12. HEATING ELEMENT Each boiler has independently operated heating elements. The element for the steam boiler receives electrical power from the pressure switch. The elements for the coffee boiler receive electrical power from the thermostat. As electrical power is applied to the element it heats the surrounding water in the boiler. 13. CONTROL BOX The control box is the most complicated component in the machine. It can be divided into the following systems: 1) Power supply: Converts high voltage AC into 18 volts DC (to power the relays) and 5 volts DC (to power the microprocessor and logic circuits). 2) Autofill system: This circuit monitors the signal from the autofill sensor and determines if it has established a ground. 3) Input system: These are the ribbon cables that carry information between the menu button pads and the control box. 4) High voltage output: This provides power to the coils and pump motor when the machine is called to brew espresso, fill the steam boiler or dispense hot water for brewing espresso. 5) Power supply: This consists of a transformer, and a40ma fuse. The fuse protects the components in the event that something has failed or shorted in the DC system. The transformer is the cube on the board. Its purpose is to reduce the high AC voltage to 18 volts AC. with the help of a series of diodes it is converted to DC voltage. 14. PRESSURE SWITCH The micro pressure switch controls the steam pressure in the rear boiler by activating a contactor which supplies power to the heating elements. When the steam pressure lowers in the boiler (usually 1.1 or 1.2 bar) the contacts close allowing power to flow from the bottom leads through the top leads and then to the heating element. As the steam pressure builds and reaches 1.5 bar the micro switch cuts the power to the heating elements.
La Marzocco Machines Basic Guideline 1 What should I do to maintain my espresso machine? 2
1. Clean the group heads daily. A. Gently remove the basket from the portafilter, using a small flathead screwdriver. Complete this maintenance sequence daily for each group and portafilter. B. Remove basket. Place portafilters and baskets in a PuroCaff solution (1 spoon every 1/2 liters). Leave to soak for ten to fifteen minutes. 3 1 C. Install a blind insert into the portafilter. Pour PuroCaff (1 teaspoon) into the blind filter and install the portafilter into the group. D. Cycle the group on and off. Run for thirty seconds, then turn off for ten seconds. Repeat by turning on for five seconds and off for five seconds, for ten iterations. Then remove portafilter and dump dissolved coffee oils and residue into the drain tray. 4 2
E. Rinse blind filter under group head until water flows clear. F. Clean remaining coffee grounds from the portafilter engagement area with a cleaning brush. 5 3 G. To remove residual detergent, install portafilter with an empty blind insert into the group and flush for five seconds. Repeat ten times. H. Re-season the group by brewing and discarding few shots of espresso. 6 4
I. Now remove baskets and inserts from the PuroCaff solution and rinse thoroughly. L. Verify that the basket spring is seated in position. Reassemble portafilters and install at each group. 7 5 2. Clean the diffuser screens and groupheads daily. A. Remove the portafilter from the group. Loosen the diffuser screw using a stubby flathead screwdriver. Remove the diffuser screw and screen assembly. B. Mix a solution of PuroCaff. (ONE table-spoon of PuroCaff per 1/12 liter of hot water.) Place the diffuser screen and screw into the PuroCaff solution. 8 6
C. Gently scrub the diffuser and portafilter gasket and portafilter engagement area. D. Dip a bar towel into the PuroCaff solution and thoroughly wipe down the grouphead area. 9 7 E. Remove diffuser screen and screw from solution. Rinse thoroughly in clean water. F. Re-assemble screen and screw. Reinstall. Backflush the group using a blind portafilter insert to rinse any remaining PuroCaff solution from the grouphead.) 10 8
Replace portafilter gaskets A. Using a stubby flathead screwdriver remove the diffuser screen and screw assembly. B. Now, using a sharp awl or pick pierce the gasket surface. (NOTE: Old gaskets may harden, resulting in a more difficult task.) Pry the gasket from the group head and discard. 11 9 C. Apply food-grade lubricant to the new gasket along the upper flat side. (NOTE: This edge sits against the group head.) D. Position gasket into group head. Press firmly into the diffuser block groove. 12 10
F. Seat the gasket by partially inserting one side of the portafilter then the other. G. Now, completely engage the portafilter. (NOTE: If the gasket is not fully seated, greater than normal pressure may be required to engage the portafilter.) Reinstall the diffuser screen and screw once the gasket is securely in place. 13 11 My shot volumes are inconsistent 14 12
Relieve an airlock in your group. A. Turn power off. B. Remove top panel. 15 13 C. Loosen bleeder screw, until water bead appears. (NOTE: Slowly turn the bleeder screw for approximately 1/4 turn. It is critical not to remove the screw completely.) D. Tighten back and turn machine on. 16 14
Check the flowmeters (performed by authorized tech) 17 15 Check the group valves (performed by authorized tech) 18 16
Inspect brewing system for leaks Inspect for group valve leaks at the discharge fitting and excess leaking from the expansion valve. A "slow but consistent" drip is normal. Adjust or replace as required. (see Machine Guideline topic # 7 Expansion valve) 19 17 Service the steam valve every three to four months (performed by authorized tech) 20 18
Inspect pump and expansion valve pressures 21 19 Adjust the pump using a screwdriver while extracting espressos until the dispense gauge reads 9 bars Now, while group is off, but heating element is on, turn expansion valve until the dispensing pressure reads 12 bars. 22 20
Coffee is best brewed at 9 bars of pressure. Higher pressure results in noise, caused by the expansion valve releasing excess pressure. 23 21 The expansion valve allows the excess pressure from water heating to be bled off to prevent damage to the brewing system components. It is very important that the expansion valve always be set to 12 bars. 24 22
My machine doesn t steam 25 23 Steam tip is clogged Clean steam wand tips A. Clear steam tip holes with a wire or sharp awl B. Wipe wand and clear by running steam through the tip for several seconds. 26 24
If steps A-B are unsuccessful, proceed with: C. Loosen tip using an open-end wrench and remove. D. Mix a solution of Purocaff and hot water. Soak tip for 10-15 minutes. E. Rinse the tip and wipe clean. 27 25 F. Wrap the steam wand threads with a short length of teflon tape. Install tip partially, but do not tighten yet. G. Trim excess tape from the wand. H. Tighten steam wand tip securely using an open end wrench. Steam wand tip is now clear and ready for use. 28 26
Glossary autofill system The components responsible for maintaining the correct level of water in the steam boiler. These include the autofill solenoid, autofill probe, and control box. ball valve, steam the valve used to shut-off the flow of steam from the steam tank to the steam valve assembly and wand. The ball valve allows the technician to shut-off the flow of steam and perform service to the steam wand assembly even when the espresso machine is live. basket, portafilter the semi-permeable filter located in the portafilter that allows espresso to flow while holding back coffee grounds from entering the espresso. Brain the microprocessor unit on automatic or AV espresso machines that controls the volume of water used to brew an espresso. It is programmed using the menu pad. burrs, grinding the sharp ceramic or steel plates that actually grind coffee to the desired coarseness. Espresso grinding mills come in two shapes: flat and conical. button, continuous flow The button on the menu pad that allows the operator to activate a continuous flow of water and then deactivate the flow when the desired level is reached. check valve A one-way valve that prevents hot water from back flowing from the steam and coffee boiler into the water supply lines. diffuser screen located at the group, the diffusor screen spreads the flow of water evenly over the espresso in the portafilter insert. When water flows into portfilter basket, the coffee expands and back pressure is created between the expanding coffee and the diffusor screen. dose weight the weight of coffee dispensed by the grinder into the portafilter. Typically a dose is set to 7 grams. element, heating The resistive coil inside the boiler that provides heat when electricity is run through it. Elements are located in both the coffee and steam vessels. Flowmeter The complete assembly of impeller, field, and body that measures the water required for pre-programmed shots.
gasket, element The gasket that seals the heating element to the boiler end to prevent leaking. gasket, portafilter The gasket located on the underside of the group head to which the portafilter seals. Grind The general description for the level of coarseness of the ground coffee used to brew espresso. ground connection Provides the ground reference for the autofill system. group cap The removable top cover on each group. The thermal limiter and bleed screw are located on top of the group cap. group, espresso machine The brewing head of the La Marzocco. It is completely filled with water to allow the convection of heat within and provide a high level of thermal stability for espresso brewing. impeller, flowmeter The six bladed wheel that spins within the flowmeter body. Magnets are positioned inside the impeller which provide a signal for the control box when spun under the magnetic sensor. impeller, pump A configuration of delicate graphite blades which spin rapidly and force water into the espresso machine. They are especially sensitive to particulates in the water supply. keypad Sometimes referred to as the button pad, the menu pad offers the barista a selection of preprogrammed drink options. It also allows the operator to program the machine to a specific pour volume. Portafilter The handled device used to hold ground, tamped coffee in place during brewing. The barista moves the portafilter between the coffee grinder and espresso machine. pour spout An attachment at the bottom of the portafilter that direct espresso into the cup. Generally the pour spout diverts coffee into two separate shot glasses.
power switch A three-way switch that applies power to the espresso machine. During start-up, the first position provides power to the dosing and fill system. When the machine is full, the second position is engaged to provide electricity to the heating elements. pressure gauge, double scale Measures the steam and brewing pressure in bars. The top scale relates to the steam vessel and the bottom scale relates to the brewing boiler. Typically steam pressure maintains a level of 1.5 bars. The coffee boiler typically measures 9 bars while brewing. pressure, tamping The amount of force the barista must apply to the coffee in the portafilter to achieve the desired shot time. Scale A dissolved mineral solid, usually calcium or lime that can accumulate on the inner workings of the espresso machine and eventually causing damage. sight glass A clear glass that allows the operator to view the water level in the steam boiler solenoid coil Converts electrical energy into a magnetic field that moves the plunger in the valve. solenoid plunger a rubber sealed piston that seals against a valve seat to control the flow of water through the valve Tamper A small hand held device used to apply pressure to the ground coffee prior to brewing to slow the extraction time. Thermostat A device used to regulate temperature by controlling the flow of electricity to the element in the brewing boiler. tip, steam wand A stainless steel nozzle used to direct the flow of steam into milk. valve, expansion A device that relieves excess pressure from the brewing system.