The Spirit is equipped with multiple boilers: one large steam boiler to produce hot water and steam, one boiler per group to heat water to brew coffee. Each boiler has its own electronic temperature controller system, heating element and safety devices, offering extremely precise temperature stability. Huge capacity is secured by the large steam boiler, over-rated heating elements in all boilers, double pumps and heat-exchangers inside the steam boiler, pre-heating the brew water for the large, dedicated coffee boilers.
The rear steam boiler has a total capacity of 10,5ltr (Duette) / 19.5ltr. Triplette. An electronic temperature controller gets its information through a precise and fast reacting probe, located in the steam and activates the heating element via 3 solid state relays. The heating elements provide a powerful total of 4.800Watt (Duette) / 6.000Watt (Triplette). This is divided over 3 elements, mounted on one flange. There are no moving parts in the complete heating system. Each element is connected to a control light. Combined with the temperature controller`s display and the control light on the SSR, this enables for a quick visual control to check from outside of machine whether all parts in the heating system function as intended.
The steam boiler is made in pure copper. Copper in general is more resistant to aggressive water than stainless steel, has a much longer life expectancy in an espresso machine. A second reason to choose copper is the use of heat-exchangers to pre-heat water for the coffee boilers. To exchange heat from the hot water in the steam boiler to the water inside the HX, a good heat transferring material is required. Copper is about the best to transfer heat. When using copper HXs, it is common sense to have the entire steam boiler in copper, to prevent any problems caused by different expanding/retracting characteristics.
The steam valve, activated by the lever at right or left with the red knobs, is an electrically activated solenoid valve with a large passage. This solenoid valve is either fully open, or closed. To adjust the steam flow/power there is an extra, horizontal lever. When adjusted, the activating lever opens the valve always immediately at the preferred flow. When necessary, the flow/power can still be adjusted on the fly by the horizontal lever.
The hot water lever, in the centre with red knobs, activates two solenoid valves simultaneously. Hot water from the steam boiler passes through one valve, the other supplies cold water. A pump runs during the supply of cold water. Cold water supply is restricted by a jet under the solenoid valve.
This mix of hot and a bit of cold water results in a steady, non-spattering stream from the hot water spout. The temperature of this mix can be managed by adjusting the pressure of the pump. A lower pressure supplies less cold water, resulting in a higher temperature from the spout. A higher pressure supplies more cold water to the mix, this results in a lower temperature. The pump pressure can be adjusted over a wide range, so the temperature of the hot water can be tuned accurately. To ensure the hot water is always at identical temperature, the machine is programmed to not activate re-filling the steam boiler during hot water supply, as this would cause a slight drop in pump pressure, resulting in a slight raise in temperature of the hot water.
Coffee water boiler with group
The coffee water boiler is made from 3mm stainless steel tube and 6mm thick flanges. There is a large hole on top of the coffee water boiler over which the group is installed. The group is made in 4 and 5mm stainless steel. All stainless is 316L. The group head is welded to the group neck, the group neck in turn is welded to the boiler. All welding is done both on the outside as well as the inside to prevent possible crevices which would easily start corrosion. The neck of the boiler is situated vertically, with a slight slope, to allow for a proper constant thermo-siphon heat flow inside, reaching the full length and height of the group. Both the cover as well as the bottom of the group are removable, sealed by O-rings.
The 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 degrees C. It is cooled down by an efficient flow-cross of the outgoing hot water with the incoming cold water.
At entering the coffee boiler the water first travels through an internal tube over the entire length of the boiler to accommodate quickly to the temperature present inside the coffee water boiler.
The temperature of the coffee 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 900Watt 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 by just pushing a button at the front of the machine. It is adjustable to 0.1 degrees Celsius.
The controller offers an Eco mode, dropping temperature half way 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 sits right under the group`s cover. This 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 grounds..
Law of nature demands a thermo-syphon flow will commence. Water heated by the heating element will go up. In the Spirit system this flow continuous to the very end of the group head. There it will cool slightly and travel downwards again to the bottom of the boiler. The neck and group are specifically designed to offer ample space allowing the hot 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 cover.
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 neck, right above the boiler. A position as hot as possible. The valve itself is entirely made in stainless steel. Brass would soak up just a bit more heat from the water passing through it.
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 cover, 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 virtually horizontal inside the group neck. This path makes for an extra temperature stabilizing effect.
The stainless steel bottom plate of the group sits at a low position, under the water. 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 directly enters the dispersion block. This block is made in a polymer plastic, a fully 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 rubber 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 rubber gasket ring sits against the bottom of the group. At the bottom of the group a small outward ridge is machined. This ridge is pushed into the rubber gasket each time the filter holder is locked into the group, as an extra sealing surface. The slight moving up of the gasket ring, because of the flexibility of the rubber, provides an ergonomically correct, soft comfortable feel for the barista. Full sealing is achieved without having to pull the filter holder firmly. The rubber group gasket is made in a heat resistant material that does not harden and go brittle. It remains flexible.
The group screen reaches up and sits against the bottom of the group. This makes it very strong. Together with the rubber 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 deforming. 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-estimated.
Machines with a slight variation in brewing temperature tend to offer a larger spectrum of different flavours from the coffee grounds. On machines offering a very strict temperature a well-executed pre-infusion becomes imperative, otherwise they might not be able to extract the full range of complexities hidden in the coffee.
Properly infusing the grounds makes for an even wetting and swelling of the grounds. This careful wetting and slow swelling ensure the chance on channelling becomes much smaller. This procedure also locks in the fines, preventing them from travelling downwards and clogging the filter.
Even more importantly however, pre-infusion allows a slow 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. All the smaller coffee particles together offer a larger surface making it easier to wash out the oils and fats.
When the brew process is started by moving the lever down, both the group solenoid valve opens and the pump starts to run.
A 0.6mm jet is positioned ahead of the coffee water boiler, in the tube running from HX to coffee water boiler..
The pressure of the pump struggles to pass the tiny 0.6mm jet. At the same time the group solenoid opened, this has an orifice of 1.5mm.
As soon as the solenoid opened water runs through the empty tube from solenoid to coffee, pushed out by the pressure inside the coffee boiler. There is always some pressure inside the coffee boiler, because of the heat. Water reaches the coffee grounds and sinks into the coffee bed. All pressure inside the coffee boiler vanishes, because lots of empty spaces had to be filled: tube, dispersion block and coffee bed.
The result is a soft and full saturation of the coffee grounds, with no pressure at all.
Then the pump finally succeeds in pushing enough water through the 0.6mm jet and slowly re-pressurizes the complete coffee boiler system till full 9 bar extraction pressure. This build-up of pressure is steady and slow, ensuring the integrity of the puck remains unaltered.
The pressure gauge is connected to the coffee boiler. This means that as soon as the solenoid valve opens there is one 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 develop.
A Spirit standard comes with two pumps. One for the coffee system, the other for filling the steam boiler and supplying cold water to add at the hot water spout. This way both functions can be used without fear of some loss of pressure. Steam boiler will be filled, even when for several hours on end at least one group is being used, as happens in truly busy bars.
As an option one pump per group is offered, to ensure no loss of extraction pressure whatsoever between the groups.
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 temperature controllers, and thus the heating elements, when the lower probe detects water. During filling up, the coffee boilers fill sooner than the steam boiler because filling starts immediately when the water connection is opened. Also, 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 deactivates the fill solenoid and pump. These are activated as soon as the higher probe does not detect water.
All electronic temperature controllers 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. Each coffee boiler 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.