In 2018, we came across the first espresso machines with thick film heaters. In 2024, the technology of the thick film heater has arrived on the espresso machine and coffee maker market as Flow Through Heater, Fast Through Heater or ThermoJet. Thick film heaters have not only overtaken the thermoblock in terms of performance and flexibility, but are increasingly putting pressure on manufacturers of traditional espresso machines with boilers.
In 2018, we tested the Sage Bambino from Australian manufacturer Breville, which operates in Europe under the name Sage Appliances. The machine was impressively fast to reach temperature, but left something to be desired in terms of temperature consistency. Shortly after, the Sage Barista Pro also made it to our test bench, and by then it became clear: the potential of thick film heaters is enormous.
Both machines were equipped with a thick film heater from Dutch company Ferro Techniek. While Sage introduced its "thick film heaters" with the trendy marketing name "ThermoJet", the heating elements are called Flow Through Heater by the manufacturer itself. How the "Flow Through Heater" works, which machines it now appears in, and what that means for the market is the subject of this article.
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: the thick film heater. And they are in good company. Because the Tone filter coffee machine, the Aiden Precision Coffee Maker and the ETNA milk system also rely on the thick film heater. The list of manufacturers using thick film heaters from Ferro will soon be joined by two more innovative espresso machines: Roxy Espresso and nunc.
Ferro Techniek
What a remarkable success story the Dutch company from Gaanderen in Gelderland can boast. The company specializes in thick film heating elements printed on metal substrates and offers tailor-made solutions for various industries. Ferro is part of the Otter Control Group and produces in the Netherlands, Hungary, Great Britain, China and southern China in partnership with Otter. Around 50 employees work at the headquarters in Gaanderen, with a further 80 in Budapest at Ferro Electronics. The Otter Group has approximately 1,500 employees worldwide.
The history of Ferro's Flow Through Heater gained momentum in 2013. The manufacturer put together a "developer kit" that contained everything needed to build prototype applications. The kit included the FTH MK2, 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 in 2007, the so-called "FTH MK1". However, this could handle 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 are required depending on the pump.
The "FTH MK2", which is suitable for espresso and can also generate steam for frothing milk, was completed in 2010 as a proof-of-principle. Production of the FTH was then ramped up in 2015, with Sage/Breville serving as a first mover crucial to the success story of the thick film heater.
Electrical power measurement log 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 enables extremely fast heating times since only a small amount of water needs to be heated. For example, the Maro Model 1 requires only 4 minutes to reach operating temperature. The Zuriga E2 Generation 2 even heats up in just 2 minutes. The thick film heater is even faster to be ready. It is the more sluggish thermal elements – such as 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 from keeping large amounts of water warm. The Zuriga E2 Generation 2 achieves a peak value 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 accurate and fast regulation of the water temperature. This is crucial for espresso extraction, as temperature fluctuations can negatively affect the taste of the coffee. The Maro Model 1 sets new standards here and, after just 4 minutes, is already among the three most precise espresso machines in terms of temperature stability that we have ever measured. This comparison also holds up well with boilers that have been heated for a longer period and have reached their thermal equilibrium. Interestingly, it is possible to adjust the temperature both upward and downward quickly. In boiler espresso machines, especially cooling down is tedious due to the high thermal mass.
The FTH is equipped by default with an NTC sensor that measures the temperature in the water channel.
Performance peaks in steam generation:
The actual potential of thick film heaters is evident in steam generation. The heaters are ready for use within seconds.
Suitability for frequent use:
The performance of the Maro espresso machine with its 2300-watt FTH demonstrates that the technology is suitable for commercial use in principle. We observed no loss of performance in either the WBC temperature protocol or in steaming.
Compact design:
The small size and flat design of the FTH allow for the development of more compact espresso machines or the integration of the FTH into the brew group, for example to heat the portafilter. Ferro offers specifically for the group a flat 60W thick film heater that can be integrated into the brew group of the portafilter espresso machine.
No waiting time for temperature:
The thick film heater is immediately ready to use. It requires virtually no preheating time. It is the other components, such as the portafilter, supply pipes and brew group, that need to be brought up to temperature first.
Less scaling:
Ferro indicates that there is less limescale buildup in the thick film heater. The reasons for this could be that no water remains standing in the thick film heater. Independent descaling of the thick film heater is in any case possible – unlike many boiler espresso machines.
How do thick film heaters work?
The water to be heated usually flows through a channel that is integrated into the substrate of the thick film heater. This channel can have various shapes to optimize the flow of water and maximize heat transfer.
Here are some important points about channel construction:
- Material: The channel is typically made of the same material as the substrate, usually 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 through 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 inlets and outlets of the channel are connected to the water supply and drainage 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 shape of the channel can be designed so that the flow velocity and turbulence of the water are optimized, which contributes 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 accurate temperatures, temperatures fluctuate significantly in others. The thick film heater allows for very precise temperature control and measurement. 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 monitoring of temperature and dynamic adjustment of heating power to keep the desired temperature constant.
By default, an NTC temperature sensor is housed 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 simpler to implement but may result in lower measurement accuracy.
A control loop is used to regulate the heating power, which compares the measured values of the temperature sensor with the setpoint and adjusts the heating power of the FTH accordingly.
Modern FTH systems often use microcontrollers to handle the control. These enable highly precise and flexible regulation of heating power depending on various parameters, such as:
- Water temperature: The microcontroller monitors the temperature of the water in the heating channel and adjusts the heating power of the FTH so that the desired temperature is reached and maintained.
- Water flow rate: In some applications, such as coffee machines, the water flow rate may vary. The microcontroller takes these fluctuations into account and adjusts the heating power accordingly to ensure the desired outlet temperature.
- Time-dependent control: In some applications, it may be necessary to vary the temperature of the water over a specific period. The microcontroller can precisely control these time-dependent temperature profiles to, for example, create optimal brewing conditions for different coffee varieties.
The integration of temperature sensors and microcontroller-based control enable highly precise and flexible temperature regulation in FTH systems.
This makes these systems an ideal solution for applications that require fast and accurate heating of water or other fluids, such as in coffee machines, water heaters and industrial processes.
Different systems, different FTHs
Already in the espresso machines we tested, we encountered different Flow-Through-Heaters from Ferro. While the Maro uses the strongest 2300-watt element possible in our test circuit, the Sage Bambino manages with the FTH II 1500 W. Zuriga, on the other hand, uses a 1400-watt model for steam generation and brewing, as well as a 600-watt model in the group to heat the portafilter.
Challenges and future prospects
Precise FTH control presents a challenge because it reacts very quickly and temperature fluctuations can occur if the control is not optimally tuned. Unlike the boiler, there is almost no thermal mass to help stabilize the target temperature.
This requires sophisticated sensors and control technology. We see that this doesn't always succeed, especially with some early models from manufacturer Sage/Breville. Sage's effort to integrate the technology broadly into the market is highly commendable. While with early models like the Bambino and Barista Pro, fluctuations were expected due to the new application of the technology, there has been plenty of time to make development steps. However, our initial tests of the Sage Oracle Jet suggest that there is still room for improvement here.
Meanwhile, other manufacturers such as Zuriga and Maro demonstrate the enormous potential inherent in thick film heater technology for espresso machines. The technology is versatile and is suitable for heating the brewing water, generating steam as well as heating the brew group and the portafilter.
I am convinced that the thick film heater has ushered in a new era in the espresso machine market. Especially for home espresso machines, the thick film heater offers exclusively advantages over boiler systems.
In a commercial context, it may be different, though we are curious about the first deployments of thick film heaters there too. Tone is working on developing a commercial espresso machine with a thick film heater, and the Maro's performance is in principle suitable for commercial use. The machine simply lacks a water connection and drainage. The performance of the thick film heaters remained stable even at high frequency and while executing the WBC protocol.
Machines with thick film heaters
This list will be updated. If you find more 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 confirmed)
- 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 date still unclear)
- maro Model 1
- Roxy Espresso
- nunc. coffee
- datum.coffee
