The Espresso Machine

0 of 51 lessons complete (0%)

Refining the Temperature

EM 3.07 An Interview with Enrico Wurm

This is a preview lesson

This course is available to members. Sign in or start a free trial.

In this lesson, we interview Enrico Wurm, product development manager at La Marzocco about the history of the saturated group, and the legendary GS machine. Enrico is a hugely experienced machine technician, managing LM’s Service Department for over ten years, whilst also heading up machine technician training programs around the world. Enrico also has a decade of experience as a Technical Judge at World Barista Championships. Enrico has a love of history, and a particular interest in the evolution of espresso technology. 

Enrico also gives us an insider’s glimpse at the motivations and interests of the Bambi brothers, Giuseppe and Bruno. Giuseppe was originally trained as a brass artisan in the 1920s, but when he first moved into espresso machine fabrications, in the words of Enrico, ‘he’d always had a fixation for stainless steel’


Barista Hustle – Does the GS design represent the first time La Marzocco (LM) used a saturated group head?

Enrico Wurm – Yes, the GS was the first design with the distinctive brass-steel junction through-bolt and cage-flange. (See pictures by my dear friend Paul Pratt [founder of Cafelat]). 

However, the first multiple-boiler machine made by LM was the Poker, built between 1964 and 1970. Through its complex hydraulic system, the Poker machine developed the pressure needed to extract the espresso. Basically, it worked the same as a lever machine, but instead of having a piston compressed by a lever, the Poker piston was operated by a diaphragm. The diaphragm was a flat, balloon-like disc that was inflated by the pressure developed by the steam boiler.

The water for the espresso was stored in a separate boiler, because the Bambi brothers had to face the big challenge of keeping this huge system at the right temperature. This was the beginning of the dual-boiler era, at least for La Marzocco. 


BH Which came first, the switch to steel boilers or the saturated group head design? Or were these technologies interdependent?

EW – Mr. Bambi always had a fixation for stainless steel. Despite the fact that stainless steel is very difficult to weld and machine, the Bambis really appreciated its durability and hygiene.


BH – We understand that a benefit and a challenge of fabrications involving stainless steel are steel’s relative insulating properties, compared with those of brass and copper. Was the GS head made entirely of brass? Are the modern GS3 and Strada groups made of steel, brass, or a combination of these materials?

EW – The LM groups were made of galvanically nickel-coated brass groups until 2006. With the advent of GS3 in 2006, we gradually transitioned to solid AISI316L [stainless steel] groups on all machines.


BH – Can you explain how the water in the boiler and in the group interact? (Is the design intended to encourage a syphon of hotter water in the boiler and cooler water in the group?)

EW – That’s easy. Hot water goes up, cold water goes down.


BH – Was the original GS brew boiler insulated? (If not, when did LM first add insulation to their brew boilers?)

EW – We introduced boiler insulation with the GS3 in 2006 (on the steam boiler) and in the Strada EP in 2009 on both coffee and steam boilers.


BH – Over time, LM has been able to lower the offset temperature between the water in the boiler and the water at the group head. How big do you think the offset would have been in the original GS machine? What is the typical offset in a modern machine such as the Strada?

EW – The modern machine’s offset is around 3°C, which is already embedded in the machine software, so the barista sees on the display the actual temperature of the water touching the coffee puck

The offset in the original GS was pretty much the same, since its hydraulic circuit and design did not change much. However today’s machines have a “smarter” PID control that minimises the temperature fluctuation, in particular during intense work cycles, so today’s machines are much more stable.


BH – What are the advantages (if any) of reducing the offset temperature between the group and the boiler?

EW – Today, we are introducing models in which we have multiple heating elements placed in different boiler areas (e.g, the Linea Mini and Leva). In the Leva, for instance, we have three temperature probes (boiler, group, and bayonet ring) and three elements placed in the same areas. They monitor, control, and display the exact temperature of the water touching the coffee. The Mini has a probe in the coffee boiler and on the integrated group brew-screw system. Reducing the offset improves the barista’s ability to dial in the machine temperature.


BH – Please help us get to the bottom of an urban myth about the origins of the dual-boiler system. Some people say manufacturers such as LM began using two boilers because the government imposed a reduced tax on smaller boiler capacities. I’m not sure whether it was the end user or the manufacturer who was supposed to pay the tax on the boilers in this story. Is there any truth to this tale?

EW – I have also heard this rumor. I suppose it comes from a chat between Mr. Bambi and James Hoffman, who might have misunderstood Mr. Bambi’s explanations. (Mr. Bambi’s English was pretty basic.) 

A combination of lost-in-translation and romance might be the origin of this myth. It is true that in the past (around 10 years ago) in China, machines with big boilers were subject to higher import duties (this explains the success of LM-home machines, even in professional environments, over there), but this [happened well before] we decided to make double-boiler machines. Probably, this was the origin of this rumor.


BH – In the noughties, a directive from baristas seems to have driven the development of new multi-boiler machines. The idea was that smaller boiler capacities were needed to improve the condition of the water hitting the coffee. Folks believed that either the water would go stale in the boiler or, somehow, the chemistry of the water could change if 6 litres instead of 500 millilitres of water sat around in a brew boiler. Is there any proof to support the idea that smaller boiler capacities can benefit coffee flavour? And do they improve temperature stability?

EW – We started building smaller boilers because we started building machines with independent boilers for each group, in order to allow baristas to brew different coffees on the same machine at the same time.

The smaller LM boiler is 1.4 litres. When flushing the group with no portafilter inserted, the flow rate is around 600 millilitres/minute. This means that you replace the whole water mass contained in the boiler in less than 3 minutes.

So, if you are busy enough, the water never goes stale. 

Bigger does not mean more stable. Stability is achieved with accurate probes, responsive heating elements, a powerful CPU, and innovative software.

—Enrico Wurm


BH – What can you tell us about the popularity of the GS and Linea machines over time?

EW – I’m not sure about GS, but Linea Classic and Linea PB are still the top-selling machines in many markets.