In 2018, we first encountered espresso machines with thick-film heaters. By 2024, thick-film heater technology, known as Flow Through Heater, Fast Through Heater, or ThermoJet, has arrived in the espresso and coffee machine market. Thick-film heaters have not only surpassed thermoblocks in terms of performance and flexibility but are also increasingly putting pressure on manufacturers of traditional espresso machines with boilers.
In 2018, we tested the Sage Bambino from the Australian manufacturer Breville, which operates in Europe under the name Sage Appliances. The machine was impressively fast to heat up, but its temperature consistency left something to be desired. Shortly after, the Sage Barista Pro was also on our test bench, and it became clear: the potential of thick-film heaters is enormous.
Both machines were equipped with a thick-film heater from the Dutch company Ferro Techniek. While Sage introduced its "thick-film heaters" with the trendy marketing name "ThermoJet," the heating elements are referred to as Flow Through Heaters by the manufacturer itself. This article will discuss how the "Flow Through Heater" works, which machines now feature it, and what this means for the market.
Maro, Zuriga, Sage and Co.
What do Maro, Zuriga Generation 2 and Unica have in common with Sage Bambino and Sage Barista Pro? They share a heating technology, namely the thick-film heater. And they are in good company. Because the Tone filter coffee machine, the Aiden Precision Coffee Maker or the ETNA milk system also rely on the thick-film heater. The list of manufacturers who rely on thick-film heaters from Ferro will soon be extended by two further innovative espresso machines: Roxy Espresso and nunc.
Ferro Techniek
What an astonishing success story the Dutch company from Gaanderen in Gelderland can tell. The company specializes in thick-film heating elements printed on metal substrates, offering tailored solutions for various industries. Ferro is part of the Otter Control Group and produces in the Netherlands, Hungary, UK, China, and southern China together with Otter. Around 50 employees work at the headquarters in Gaanderen, with another 80 at Ferro Electronics in Budapest. The Otter Group has approx. 1500 employees worldwide.
The story of Ferro's Flow Through Heater took off in 2013. The manufacturer put together a "developer kit" that included everything needed to build prototype applications. In addition to the FTH MK2, the kit also included a pump, a flow meter, and a control board. This kit was ordered by around 100 companies.
Interestingly, Ferro had already developed an older version of the FTH, the so-called "FTH MK1", in 2007. However, this could only process a maximum of 2.5 bar pressure and was therefore used in machines with pads. For brewing espresso, pressure standards of up to 15 bar, depending on the pump, are necessary.
The "FTH MK2", which is suitable for espresso and can also generate steam for frothing milk, was completed as a proof-of-principle in 2010. Production of the FTH was then ramped up in 2015, with Sage/Breville being central to the success story of the thick-film heater as a first mover.
Power measurement protocol of the Maro Model 1 recorded by us.
What are the strengths of the thick-film heater?
The thick-film heater has several advantages over boilers and thermoblock systems.
Fast heating times:
The low thermal mass of the FTH allows for extremely fast heating times, as only a small amount of water needs to be heated. The Maro Model 1, for example, only needs 4 minutes to reach operating temperature. The Zuriga E2 Generation 2 even heats up in just 2 minutes. The thick-film heater is always ready even faster. It is the slower thermal elements – like the portafilter – that lag behind the Flow Through Heater.
Energy efficiency:
FTH systems are more energy-efficient than boilers because they heat on demand. This avoids energy waste by keeping large amounts of water warm. The Zuriga E2 Generation 2 reaches a peak of 0.058 kWh for 5 double espresso shots including heating time. The Maro Model 1, Sage Bambino and Co. are equally efficient. For comparison: Many espresso machines with boilers use 0.2 to 0.5 kWh for 5 espresso shots including heating time.
Precise temperature control:
The flat design and direct heat transfer of the FTH enable very precise and rapid control of water temperature. This is crucial for espresso extraction, as temperature fluctuations can negatively affect the coffee's taste. The Maro Model 1 sets new standards here and, after just 4 minutes, is one of the three most precise espresso machines in terms of temperature stability that we have ever measured. This comparison also holds true against boilers that have been heated for a longer period and have reached their thermal equilibrium. It's interesting that rapid temperature adjustments, both up and down, are possible. With boiler-based espresso machines, cooling down is particularly time-consuming due to the high thermal mass.
The FTH is standardly equipped with an NTC sensor, which measures the temperature in the water channel.
Power peaks during temperature impact:
The true potential of thick-film heaters is revealed in steam generation. The heaters are ready for use within seconds.
Frequency suitability:
The performance of the Maro espresso machine with its 2300-watt FTH shows that the technology is, in principle, also suitable for gastronomy. We found no performance degradation either in the WBC temperature protocol or during frothing.
Compact design:
The small size and flat design of the FTH enable the development of more compact espresso machines or the integration of the FTH into the brewing group, for example, for heating the portafilter. Ferro offers a flat 60W thick-film heater specifically for the group, which can be integrated into the brewing group of the portafilter espresso machine.
No waiting time for temperature:
The thick-film heater is ready for immediate use. It requires virtually no preheating time. It is the other components, such as the portafilter, connecting pipes, and brew group, that first need to be brought up to temperature.
Less limescale:
Ferro states that less limescale formation occurs in the thick-film heater. Reasons for this could be that no standing water remains in the thick-film heater. In any case, independent descaling of the thick-film heater is possible – unlike with many boiler-based espresso machines.
How do thick-film heaters work?
The water to be heated typically flows through a channel integrated into the thick-film heater's substrate. This channel can have various shapes to optimize water flow and maximize heat transfer.
Here are some key points about channel construction:
- Material: The channel is usually made of the same material as the substrate, typically stainless steel.
- Shape: The channel can have a simple tubular shape or more complex geometries to influence water flow and create turbulence.
- Integration: The channel is integrated into the substrate using special manufacturing processes, such as deep drawing.
- Sealing: After the channel is manufactured, the inlets and outlets are sealed to prevent water leakage.
- Connection: The channel's inlets and outlets are connected to the water supply and drainage lines of the device in which the FTH is used.
By integrating the channel into the FTH substrate, direct and efficient heat transfer from the heating element to the water is ensured. The channel's shape can be designed to optimize the water's flow rate and turbulence, contributing to faster and more uniform heating.
Integration and control of temperature sensors
We have already tested many of the espresso machines mentioned above for their temperature stability. While some manufacturers achieve very precise temperatures, temperatures fluctuate widely in others. The thick-film heater allows for very precise control and measurement of temperature. However, a very good control loop is necessary to achieve precise temperatures.
The integration of temperature sensors and the associated precise control are crucial aspects for the optimal functioning of thick-film heaters (FTH). They enable accurate temperature monitoring and dynamic adjustment of heating power to maintain the desired temperature constantly.
A standard NTC temperature sensor is placed in the water channel to measure the temperature of the flowing water as accurately as possible. There are various placement options. This method offers the highest accuracy but requires waterproof encapsulation of the sensor.
Alternatively, the sensor can be mounted on the surface of the substrate near the channel. This method is easier to implement but may lead to lower measurement accuracy.
A control loop is used to control the heating power, which compares the measured values of the temperature sensor with the setpoint and adjusts the FTH's heating power accordingly.
Modern FTH systems often use microcontrollers to handle the control. These enable highly precise and flexible control of the heating power depending on various parameters, such as:
- Water temperature: The microcontroller monitors the water temperature in the heating channel and adjusts the FTH's heating power so that the desired temperature is reached and maintained.
- Water flow rate: In some applications, such as coffee machines, the water flow rate can vary. The microcontroller takes these fluctuations into account and adjusts the heating power accordingly to ensure the desired output temperature.
- Time-dependent control: In some applications, it may be necessary to vary the water temperature over a specific period. The microcontroller can precisely control these time-dependent temperature profiles to create optimal brewing conditions for different types of coffee, for example.
The integration of temperature sensors and microcontroller-based control enables highly precise and flexible temperature regulation in FTH systems.
This makes these systems an ideal solution for applications requiring fast and accurate heating of water or other liquids, such as coffee machines, water heaters, and industrial processes.
Different systems, different FTHs
Even with the espresso machines we tested, we encountered different Flow-Through-Heaters from Ferro. While the Maro relies on the most powerful 2300-watt element possible in our circuit, the Sage Bambino uses the FTH II 1500W. Zuriga, in turn, uses a 1400-watt model for steam generation and brewing, and a 600-watt model in the group for heating the portafilter.
Challenges and Future Prospects
Precise control of FTHs presents a challenge, as they react very quickly and temperature fluctuations can occur if the control is not optimally tuned. Unlike with boilers, there is almost no thermal mass to help stabilize the target temperature.
This requires sophisticated sensor technology and control engineering. That this doesn't always succeed is something we primarily see in some early models from the manufacturer Sage/Breville. Sage deserves great credit for integrating the technology across the market. While fluctuations were to be expected with the first models like the Bambino and Barista Pro due to the new application of the technology, there was plenty of time to make development strides. However, our initial tests of the Sage Oracle Jet indicate that there is still room for improvement here.
Meanwhile, other manufacturers like Zuriga and Maro demonstrate the enormous potential of thick-film heater technology for espresso machines. The technology is versatile and suitable for heating brewing water, generating steam, and heating the brew group and portafilter.
I am convinced that with the thick-film heater, a new era has begun in the espresso machine market. Especially for home espresso machines, the thick-film heater offers exclusively advantages over boiler systems.
In a gastronomic context, it may be different, although we are also eager to see the first uses of thick-film heaters there. Tone is working on developing a commercial espresso machine with a thick-film heater, and the performance of the Maro is, in principle, suitable for gastronomy. The machine only lacks a water connection and drain. The performance of the thick-film heaters was stable even at high frequency and during the execution of the WBC protocol.
Machines with thick-film heaters
This list will be updated. If you find other machines with thick-film heaters, please let us know in the comments:
- 2019: Sage/Breville Bambino (FTH II 2300W)
- 2018: Sage/Breville Bambino Plus (FTH II 2300W)
- 2020: Sage/Breville Barista Pro
- 2021: Sage/Breville Barista Touch
- 2022: Unica Pro (FTH II 1800W, to be clarified)
- 2022/23: Tone Filter Coffee Machine
- 2024: Sage/Breville OracleJet
- 2024: Maro Model 1 - (FTH II 2300W)
- 2024: Aiden Precision Coffee Maker
- 2024: Zuriga Generation 2: (FTH II 1400W)
- ETNA Milk System
- Tone Espresso Machine (prototype presented at Host 2023. Launch still unclear)
- Roxy Espresso (announced for 2025)
- nunc. coffee (announced for 2025)
