The thick film heater era has begun!

In 2018, we encountered the first espresso machines with thin-film heaters. In the meantime, thin-film heater technology as Flow Through Heater (FTH), Fast Through Heater, or ThermoJet has arrived in the espresso machine and coffee machine market. Thin-film heaters have not only surpassed the classic 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 at reaching temperature, but left something to be desired in terms of temperature stability. Shortly afterwards, the Sage Barista Pro also arrived at our test bench, and by then it became clear: the potential of thin-film heaters is enormous.

Both machines were equipped with a thin-film heater from Dutch company Ferro Techniek. While Sage introduced its thin-film heaters with the trendy marketing name "ThermoJet", the heating elements are called Flow Through Heater by the manufacturer themselves. How the Flow Through Heater works, which machines it appears in by now, and what this means for the market is the topic 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 thin-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 thin-film heaters. The list of manufacturers using thin-film heaters from Ferro will soon be expanded by two more innovative espresso machines: Roxy Espresso and nunc.

The history of Ferro's Flow Through Heater gained momentum in 2013. The manufacturer compiled a "developer kit" that included everything needed to build prototype applications. Part of the kit, along with the FTH MK2, were a pump, a flow meter, and a control board. This kit was ordered by approximately 100 companies.

Interestingly, Ferro developed an older version of the FTH back in 2007, the so-called "FTH MK1". However, it 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 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 serving as the first mover and becoming central to the success story of the thin-film heater.

What are the strengths of the thin-film heater?

The thin-film heater has significant advantages over boiler and thermoblock systems:

How do thin-film heaters work?

The water to be heated flows through a flat channel that is directly integrated into the substrate of the thin-film heater. This channel is designed so that water flow is optimized and heat transfer is maximized.

By directly integrating the channel into the FTH substrate, immediate and highly efficient heat transfer from the printed resistance element to the flowing water is ensured.

Integration and control of temperature sensors

The flat design and rapid response time require highly precise sensor technology and control electronics. Since there is little thermal mass for buffering, the control system must regulate in real-time:

Different systems, different FTHs

Depending on the application, different FTH models from Ferro are used:

Challenges and future prospects

Precise FTH control represents one of the greatest challenges: without buffering thermal mass, inaccurate control loops immediately lead to temperature fluctuations. The complexity of integration was evident in early Sage/Breville models. While earlier generations still showed fluctuations, continued development demonstrates the enormous potential.

Manufacturers like Zuriga and Maro impressively demonstrate the performance this technology can deliver. The thin-film heater flexibly handles all tasks: heating the brewing water, generating steam, and heating the brewing group and portafilter.

Overview: Machines with thin-film heaters