In 2018, we came across the first espresso machines with thick-film heaters. By 2024, the technology of the thick-film heater has arrived in the espresso machine and coffee maker market as a Flow Through Heater, Fast Through Heater, or ThermoJet. Thick-film heaters have not only surpassed 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 by 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 landed on 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 heater" with the trendy marketing name "ThermoJet", the heating elements are actually called Flow Through Heater by the manufacturer itself. How the "Flow Through Heater" works, which machines it now appears in, and what this 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're in good company. 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 expanded 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, offering custom solutions for various industries. Ferro is part of the Otter Control Group and manufactures in the Netherlands, Hungary, the United Kingdom, China, and southern China in partnership with Otter. Approximately 50 employees work at the headquarters in Gaanderen, with another 80 in Budapest at Ferro Electronics. The Otter Group has approximately 1,500 employees worldwide.
The history of Ferro's Flow Through Heater picked up momentum in 2013. The manufacturer put together a "developer kit" that contained everything needed to build prototype applications. In addition to the FTH MK2, the kit included a pump, a flow meter, and a control board. This kit was ordered by approximately 100 companies.
Interestingly, Ferro had already developed an older version of the FTH, the so-called "FTH MK1", back in 2007. However, this could only 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 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 as first movers playing a crucial role in the success story of the thick-film heater.
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 allows extremely fast heating times since only a small amount of water needs to be heated. For example, the Maro Model 1 requires just 4 minutes to reach operating temperature. The Zuriga E2 Generation 2 heats up in just 2 minutes. The thick-film heater is even faster to reach operating temperature. It is the slower 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 others are equally efficient. For comparison: many boiler espresso machines 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 rapid adjustment of water temperature. This is critical for espresso extraction, as temperature fluctuations can negatively affect the taste of the coffee. After just 4 minutes, the Maro Model 1 sets new standards and is already among the three most precise espresso machines in terms of temperature stability we have ever measured. This comparison holds up with boilers that have been heating for a longer time and have reached their thermal equilibrium. Interestingly, rapid temperature adjustments both up and down are possible. With boiler espresso machines, cooling in particular is lengthy due to the high thermal mass.
The FTH is equipped with an NTC sensor as standard, which measures temperature in the water channel.
Power peaks during temperature application:
The true potential of thick-film heaters becomes apparent 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 demonstrates that the technology is in principle suitable for commercial use. We observed no loss of performance with the WBC temperature protocol or during steaming.
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 brew group, for example to heat the portafilter. Ferro offers a special flat 60W thick-film heater for the group that can be integrated into the brew group of a portafilter espresso machine.
No wait 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, feed tubes, and brew group, that need to be brought up to temperature.
Less scale:
Ferro states that less scale formation occurs in the thick-film heater. This could be because no standing water remains in the thick-film heater. Independent descaling of the thick-film heater is indeed possible—unlike many boiler espresso machines.
How do thick-film heaters work?
The water to be heated typically flows through a channel integrated into the substrate of the thick-film heater. This channel can take various shapes to optimize water flow 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 form 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 drain 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 shape of the channel can be designed so that the flow rate and turbulence of the water are optimized, resulting in faster and more even heating.
Integration and control of temperature sensors
We have already tested many of the espresso machines mentioned above for 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 precise monitoring of temperature and dynamic adjustment of heating power to maintain the desired temperature consistently.
By default, an NTC temperature sensor is installed in the water channel to record 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 can result in lower measurement accuracy.
A control loop is used to regulate heating power, which compares the sensor readings with the setpoint and adjusts the heating power of the FTH accordingly.
Modern FTH systems often use microcontrollers to manage control. These allow for 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 in coffee machines, the flow rate of water can vary. The microcontroller takes these fluctuations into account and adjusts heating power accordingly to ensure the desired outlet 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 coffee varieties, 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 that require rapid and accurate heating of water or other fluids, such as in coffee machines, electric kettles, and industrial processes.
Different systems, different FTHs
Even among 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 circuit, the Sage Bambino gets by 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 for heating the portafilter.
Challenges and future prospects
Precise control of FTH presents a challenge because it reacts very quickly and temperature fluctuations can occur if the regulation is not optimally tuned. Unlike the boiler, there is almost no thermal mass to help stabilize the target temperature.
This requires sophisticated sensor technology and control systems. That this doesn't always succeed is evident, especially with some early Sage/Breville models. Sage's achievement in integrating the technology broadly across the market is highly commendable. While fluctuations were expected with early models like the Bambino and Barista Pro due to the novel application of the technology, there was much time to make developmental advances. However, our initial tests of the Sage Oracle Jet suggest that there is still room for improvement.
Meanwhile, other manufacturers like Zuriga and Maro demonstrate the enormous potential that thick-film heater technology holds for espresso machines. The technology is versatile and suitable for heating brew water, generating steam, and heating the brew group and portafilter.
I believe 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 nothing but advantages over boiler systems.
In a commercial context, things may be different, though we are eager to see initial deployments 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 commercial use. The machine just lacks a water inlet and drain. The performance of the thick-film heaters was stable even at high frequency and during the WBC protocol.
Machines with thick-film heaters
This list will be expanded. If you find any 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 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 unclear)
- maro Model 1
- Roxy Espresso
- nunc. coffee
- datum.coffee
