- Wide array of appearances and options.
- Very large shot timers, installed in full view, right below each group.
- Intuitive operation by levers (bastones) that offer 2 automatic shot volumes per group. The bastones can easily be replaced with touch pads that offer 4 shot volumes per group.
- Slow automatic infusion process, with stepless build-up of pressure to full extraction mode. This allows a finer grind, creating more surface, so a higher yield in the cup, less chance of channelling, preventing fines to travel down.
- 10.5 litre steam boiler has 4800 or 6000W heating power and large heat exchanger with thermo-siphon controlled distribution block.
- Electronic temperature control at distribution block feeds individual 0.8 litre self-bleeding coffee-boilers with 450W heating power each.
- Two-temperature hot water system: Either instantaneous from the steam boiler or some cold added to provide a steady, non-spattering stream with the correct temperature to prepare Americanos.
- Drip tray quickly adjustable in height, optionally a sneeze guard is available.
- Stainless steel filter holders with KvdW handles; wide choice in filter baskets, both sizes as types; enduring flexibility of group gaskets, they do not become hard or brittle.
- Membrane type group screen and polymer dispersion blocks account for very nice dispersion and will remain clean long.
- Auto-back-flush program, all groups pressurize and discharge simultaneously 8 times.
- Energy saving ECO mode for individual boilers or entire machine. Automatic ECO-OFF-ON times can be programmed.
- Heavily protected heating element (extra safety level probe, cut-out switches, machine shuts down when any of the solenoid valves remains open for longer than 120 seconds).
- Entire frame, boilers and manifolds in stainless steel only.
- Elevated position of body, easy cleaning of bar surface, yet low enough to allow comfortable barista-customer contact.
The machine has the well-known “Kees van der Westen” signature looks and is positioned between the Mirage and Spirit in looks, technics as well as in price. The group heads have the same shape as the Spirit and Speedster. Each individual group has a large 3-digit display that functions as a shot timer during brew (and shortly thereafter) before changing to display the groups’ temperature.
Optical feedback is also provided by the mechanical pre-infusion cylinders and the pressure gauges, the latter display the actual water pressure onto the coffee-bed. Elegant brew-levers (bastones) are used to activate the groups with 2 adjustable volumes per group. Easily adjustable height of the drip-tray allows for a large range of cup-sizes.
Although the main body has a defined shape, the appearance is easily changed by altering the colour-scheme of body panels, knobs and/or handles, mount different side-panels, legs, front panel, cup rail or a sneeze guard awning. We offer a series of standard colours and side-panels but we appreciate retail-chains as well as individual customers to forward their special wishes to make their machine “one-of-a-kind”.
Foot activated steam valves may be added for even quicker service. A -barista adjustable- cup heating mat can actively warm cups which may be protected from customers by a sneeze-guard. For even more systems control, an external temperature probe can be connected to the machine while the measured temperature can be read from the machines’ display. The bastones can be replaced with touchpads that offer 4 adjustable volumes per group.
The Slim Jim is equipped with multiple boilers: one large stainless-steel steam boiler to produce hot water and steam, one stainless steel boiler per group to brew coffee. A heat-exchanger with balanced cross-flow and an electronically controlled cooling circuit ensures
well-conditioned supply of pre-heated water for the coffee boilers to ensure enormous capacity in a relatively compact machine. Each boiler has its own electronic temperature control system, heating element and safety devices, offering extremely precise temperature stability at high volume.
Incorporated in the steam boiler is a very large heat exchanger (HX) that is part of a thermo-siphon loop. At the top of the thermo-siphon loop water is fed from the HX manifold block towards the individual groups. Cross-flow at the feed-side of the HX conditions the temperature of the water flowing to the manifold block. If for any reason the HX manifold block gets too hot the necessary amount of cold water is added in the flow towards the individual coffee boilers.
The coffee boilers are made from a 4mm stainless steel tube and a 10mm thick flange. The group head is made in 5mm stainless steel and is welded to the boiler. All welding is done both on the outside for looks as well as on the inside to prevent possible crevices in which corrosion is known to start. All stainless is 316L. Boiler and group head together contain approximately 0.8 litre of water.
The boiler slopes slightly to allow for a proper constant thermo-siphon heat flow inside, reaching the full length and height of the boiler and group head. Both the top and the bottom of the group head are removable, sealed by O-rings.
Cold water entering the machine is first directed through a heat-exchanger located inside the steam boiler. Exiting the heat-exchanger its temperature is higher than needed because the steam boiler runs at 125 °C. A restrictor in the circuit makes that the water in the distribution block is very close to the temperature of the coffee boilers. This way the distribution block is kept warm during idle of the machine.
Temperatureinside the distribution block is monitored with a sensor. If by any chance the water in the distribution block is too hot some cold water will be added in the flow to the individual coffee boiler when a group is activated. The water thus conditioned will have only a minor deviance from the (pre-set) temperature of the group.
Inside the coffee boiler, the temperature of the water is measured and controlled by a highly sensitive probe connected to a PID (proportional-integral-derivative) controller. This is a control loop feed-back mechanism. A nearly intelligent system, learning from the past, responding ahead, steering the 450 Watt heating element by pulses through a solid-state relay. There is no moving part in the entire heating and controlling system. This set-up ensures an extremely fast reacting system as well as a very reliable one. The water temperature can easily be changed in the Barista menu of the interface.
The controller offers an ECO mode, lowering the temperature of an individual coffee-boiler to 50 °C during longer periods of idle.
At first installation it is important all air is bled from the coffee boiler. Air can be compressed, water cannot. When the group lever activates the group solenoid valve and pump for the first time, all air is automatically expelled by the inrush of water because the pick-up tube is located directly under the group`s top which is the highest point in the system. When the heating system reaches and maintains the perfect desired temperature, the challenge this system poses is to not suffer any variation in temperature until the water hits the coffee grinds.
Law of nature demands that thermo-syphon flow will commence when changes in water temperature are present. Water heated by the heating element will go up. In the coffee system the warmer water will flow up to the very end of the group head where it will cool slightly and travel downwards again to the bottom of the boiler. The boiler and group are specifically designed to offer ample space allowing the warmer and cooler flows to pass each other. The “sweet spot”, the most stable temperature in this system, will develop at the highest point, right underneath the group top. The pick-up tube is positioned right in that sweet spot, running to the 3-way group solenoid valve. This valve is installed at the lower end of the boiler. A position as hot as possible. The valve itself is made from stainless steel.
When brewing, the water never leaves the coffee water boiler/group on its path towards the coffee. It runs via a tube inside the group, starting from directly under the group top, to the stainless steel three-way solenoid valve. Stainless transfers heat ten times less than brass, so is far more isolating. From the solenoid valve it is routed through another tube towards the bottom of the group. Both these tubes run parallel in the higher part of the boiler. This path makes for an extra temperature stabilizing effect.
The stainless-steel bottom plate of the group is at a low position. This causes its temperature to be below the temperature of the water. Water passing the bottom on its way to the coffee grounds, should not lose any of its heat to the metal bottom.
Therefore, the dispersion block reaches up through the bottom plate, so the water enters the dispersion block directly without contact with the group bottom. This block is made from polymer plastic, a nearly temperature-neutral material. As this block remains cool, the fats and oils in the coffee do not bake on, effectively keeping it clean for a long time. This block consists of two pieces offering a nicely divided dispersion of the water.
The group screen is hold in place by the surrounding group gasket. To pull out the gasket with screen for controlling, cleaning or replacing, a special tool is provided with each machine in the Barista Kit. The gasket ring sits against the group bottom that has a small outward ridge. This ridge is pushed into the gasket each time the filter holder is locked into the group, thus providing excellent sealing. The slight moving up of the gasket ring, because of the flexibility of the material, provides an ergonomically correct, soft comfortable feel for the barista. Full sealing is achieved without having to pull the filter holder firmly. The group gasket is made in a heat resistant material that does not harden and go brittle but remains flexible.
The group screen’s circumference is pushed against the bottom of the group making the screen robust. Together with the gasket surrounding the screen, it is impossible for coffee grounds to ever reach the insides of the group. The supporting horizontal base of the screen is thick to resist deformation. This base is perforated and covered with a stainless-steel membrane, not a woven mesh. This membrane provides a very even dispersion of the water during extraction. It also strongly filters the water sucked up when the pressure is discharged at the end of the shot. This again ensures a cleaner inside of the group.
The importance of pre-infusion still seems to remain under-appreciated. On machines offering a very confined brew temperature a well-executed pre-infusion becomes imperative: without they will not be able to extract the full range of complexities hidden in the coffee. Properly infusing the grounds makes for uniform wetting and swelling of the grounds which in turn reduces the danger of channelling while also locking in fines, thus preventing them from travelling downwards and clogging the filter.
Even more importantly however, pre-infusion allows a tranquil warming and softening of the fats and oils in the coffee grounds before extracting these with high pressure. This clearly results in a higher yield of solids in the cup. These fats and oils are the actual carriers of the delicate aromas and flavours. A good infusion system allows for a finer grind with larger surface area making it easier to wash out the oils and fats.
When the brew process is started by moving the lever down, the group solenoid valve is activated and the pump starts to run. A 0.6 mm restrictor is located at the supply side of this 3-way valve reducing the maximum flow-rate through the valve. After passing the group-valve the tubing splits in two: one line feeds water onto the coffee-bed, another line feeds water into the pre-infusion cylinder.
Movement of the piston of the pre-infusion cylinder is restrained by a double spring gradually increasing load while being compressed. At the same time pressure onto the coffee bed gradually increases. At about 4.5 bar the piston has reached it total travel and from that moment on brew pressure rises quickly until pump-pressure is reached. The pressure gauge is connected to the pre-infusion cylinder which means that there is an open connection all the way to the coffee puck. The gauge displays the actual extraction pressure, not just the pump pressure. The barista can monitor exactly how infusion and extraction pressure develops.
When the group-valve is de-activated at the end of a brew, pressure on the coffee bed is immediately released as flow in the valve reverses and water in the pre-infusion cylinder is pushed through the group-valve into the machine’s drain thus flushing possible very fine coffee grinds out of the valve after each brew.
STEAM AND HOT WATER
The isolated steam boiler is located at the rear of the machine and has a total capacity of 10.5 litres. (Duette and Triplette, about 75% filled with water). An electronic temperature controller gets its information through a probe located in the steam and activates the heating element via 3 solid state relays. The heating element provides a powerful total of 4.800 Watt (normal) or 6.000 Watt (high power). This is divided over 3 heating spirals mounted on one flange. There are no moving parts in the complete heating system. Each heating spiral is connected to a control light. Combined with the machine`s display this enables for a quick visual control to check from the outside of the machine whether all parts in the heating system function as intended.
The steam boiler is made in stainless steel 316L, which is more resistant against aggressive water than stainless steel 304 and has a long life expectancy in an espresso machine.
The controller offers an ECO mode, lowering the temperature of the steam boiler to about 70 °C during longer periods of idle or overnight.
As an option, the mechanical steam valves at left and/or right can be activated with an air-pedal on the floor. The air pedal on the floor activates an electrical switch inside the machine which in turn activates a solenoid valve with a large passage. This solenoid valve is either fully open or fully closed. The steam flow/power can be decreased by the use of a mechanical valve. When adjusted, the activating lever opens the valve always immediately at the preferred flow.
Hot water dispensing
Hot water can be dispensed in two manners:
1. Pressing the push button switch results in dispensing mixed water for an adjustable number of seconds. The switch activates two solenoid valves and the pump simultaneously: hot water from the steam boiler passes through one valve, the other valve supplies cold water at pump pressure. Cold water addition is restricted by an adjustable needle valve in the manifold such that the temperature of the water dispensed can be adjusted between approximately 60 and 100 °C. This mix of hot and a bit of cold water results in a steady, non-spattering stream from the hot water spout and can be adjusted to be excellent for making Americanos or green tea.
2. When the toggle switch is pressed down only the hot water valve opens which results in water flowing directly from the steam boiler to the spout. Releasing the toggle switch will stop the flow immediately. At the moment the toggle switch is pressed down the temperature of the water dispensed quickly rises to boiling point and will start to sputter. The boiling water is excellent for making black tea.
Steam boiler fill
As the Slim Jim has a single pump, factory setting is that filling of the steam boiler is prohibited while a group is active. This setting eliminates flow-rate decrease and subsequent decrease in brew-pressure during a shot. The disadvantage of this setting is that the steam boiler may never start to top-up in a high-volume location where at least one of the groups is active for uninterrupted periods of time while also dispensing hot water and, with minor impact, steaming milk. For extremely high-volume locations the setting can be changed such that the steam boiler starts filling as soon as the water level drops below operational.
The steam boiler has two probes to monitor the level of the water inside. The lower probe ends just above the heating element. When the machine is fired and filled for the first time, the brain only switches on all heating elements, when the lower probe detects water. During filling up, the coffee boilers fill quicker than the steam boiler because filling starts immediately when the water connection is opened and the coffee boilers are smaller. When the lower probe in the steam boiler detects water the elements inside the coffee boilers are already submerged. This system ensures the elements cannot be turned on while not being cooled by surrounding water.
If the steam boiler level would ever fall under the safety probes tip, the machine shuts down completely with the led at group lever or touch pad blinking as an alarm. This alarm mode is also activated when one of the group solenoids or the filling solenoid is activated continuously for longer than 2 minutes. The machine can be re-set by switching it off and on again.
When the higher probe contacts water the brain de-activates the fill solenoid and pump. These are activated as soon as the higher probe does not detect water. All temperature settings have a restricted upper temperature programmed. When this temperature is reached no more signal to the solid-state relay is sent. Each boiler is equipped with an overheating cut-out switch. When this switch detects too high a temperature, it will disconnect power to the element. The steam boiler is equipped with a safety valve. The coffee system, including the heat-exchanger, is equipped with an expansion valve.
The group solenoid valve may act as a second expansion valve, rated at 15 bar, in the event the original expansion valve would fail.