How Does An HX Espresso Machine Work?

Maybe your average espresso drinker doesn’t need to know much about the technical side of espresso making, but when you are personally about to spend hundreds if not thousands of dollars for a machine for either home use or for commercial purposes, it doesn’t hurt to know some of the technical details.

In particular, there are HX espresso machines out there, and not a lot of espresso drinkers know what they’re all about.  Of course, people who are in the know are aware.. and isn’t that always the way?  

For those educating themselves, typically, if you buy an HX espresso machine, you will find that just being “HX” means the price is bound to be higher.  But why?  What do HX espresso machines do, and how do they work?

How Does An HX Espresso Machine Work?

For starters, what does “HX” stand for?  As you can see from the above diagram, “HX” stands for “heat exchanger”.  Fair enough, but how does this apply to espresso machines in general? 

As it turns out, its all about getting that perfect temperature water for your brew, and, in the world of espresso, slight degrees really do count, as does consistency of results. 

Take a look at this diagram below, and all will soon become clear.

HX vs Dual Boiler

As you can see from the above diagram, HX espresso machines have one large steam boiler, as opposed to an espresso machine that has a dual boiler – one for steaming, and one for brewing.

When it comes to brewing, an HX espresso machine has copper tubing that runs through the steam boiler (this is called the heat exchanger), where room temperature water is run through the steam boiler via this copper tube, gets flash-heated by the higher temperature steam in the boiler, and exits the brew head at a specific temperature appropriate for brewing.

Here is a brief demo video of the Rocket Giotto Evoluzione V2, an HX espresso maker that is a prime example of what an HX espresso maker is capable of.  And also shows us that, generally speaking, when the boiling technology gets more integrated, it results in more expensive but higher quality machines.

The Importance Of The Group Head

HX espresso machines rely on a heavy, highly thermally conductive metal group head.  When it comes to the temperature, imagine the group head as a chunk of brass that has the weight of a bowling ball. 

The espresso machine’s group head works in tandem with the boiler and heat exchanger to moderate and control the temperature of the water that eventually comes into contact with your delicious coffee grinds to produce the espresso you are after.

When the water from the heat exchanger reaches the group head, the group head works as a dampener that will either reduce the temperature of the incoming water (in case it is too hot), or raise it if it’s too cold. 

This might only be a matter of a few degrees, but, when it comes to espresso, the goal is to achieve the correct temperature time and again for consistent results.

Here is a video which is rather in depth, but explains the difference between HX and double boiler espresso machines quite well.

There are many commercial espresso machines that rely on direct thermal conduction by attaching the group directly onto the boiler.

Other machines use a thermo-syphon to circulate water from the boiler through the group. 

Once the water in the heat exchanger portion of the loop warms, it rises and flows towards the group.  Then, the water cools and descends towards the bottom of the group, returning to the boiler where it reheats and repeats the circuit.

HX espresso machines are considered a sort of specialty espresso machine because they have commercial grade rotary pumps as an option, which means they can be plumbed into water mains. 

Here is a video showing how to plumb in a GS3 Espresso Machine.

HX How Does It Work…Cont.

HX espresso machines are equipped with an auto-boiler refill, pressure gauges and boiler and reservoir level sensors, which can shut off the machine in order to protect it in the event that it some sort of emergency situation occurs.

Another important thing we want to point out about HX espresso machines is about the pressure that happens in the boiler. The whole brew pathway heats up to some percentage of the boiler temperature as the hot water circulates between the boiler and group.

There is no system that has 100% thermal efficiency, which means the group head temperature will be determined by its own heat loss and that of the copper tubing carrying water to it. 

In the U.S.A., the target brew temperature is around 201-203°F; while in other countries overseas, the temperature is somewhat lower, about 192°F.

People prefer HX espresso machines because the water that is used to brew the coffee spends very little time in the machine.  The longer the water stays in the machine the more adversely this will affect the taste of your espresso.  Also, the temperature of your espresso is easier to control with an HX machine, and the consistency is very high, which is especially desirable for commercial purposes.

Popular Models of HX Espresso Machine

Rocket Giotto Evoluzione V2 (HX) Espresso Machine

Features

• Insulated Boiler
• E61 commercial group with automatic pre-infusion
• Finely crafted 304 stainless steel case
• No-Burn stainless steel hot water and steam wands
• Non-compression hot water and steam valves

Vibiemme DJHXMAVAIN Domobar Junior HX Manual Espresso Machine

Features

• Mirror-polished stainless steel body panels make it great for adding style to your kitchen!
• Unit extracts steam milk and espresso at the same time!
• Professional brass porta-filters bring style and convenience to espresso making
• The heating element can be adjusted from the top of the machine for your convenience
• Low water level light indicates when water is low in the reservoir

Bezzera Mitica Commercial Espresso Machine

Features

• Can be switched from tank model to direct plumb
• Classic E61 lever design group head
• Polished stainless steel body
• Thermo-syphon heat exchanger system
• Copper boiler with an internal heating exchanger that allows you to produce coffee, steam and hot water without delay
• Four liter water tank
• Rotary vane pump

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