Are all HX espresso machines the same?

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#1: Post by nichikumaat »

Let say I brew the same coffee, with the same dose, same brew time, same yield and with no pre-infusion but with two different hx machine. One with Bezzera b2016 and one with Simonelli appia. Will the result be the same in term of taste?

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#2: Post by another_jim »

No. Every machine is slightly different. If you have then side by side, and try to get identical tasting shots, you'll end with a different dose and grind for the two machines. This is true of HX and double boiler machines. The HX is just a way of heating the water; and there a lots of different designs and quality of execution (a solid B on both these machines, an A+ on the Appia's bigger sister, the Aurelia).

Both machines you are looking at use a fairly conventional HX coupled to a thermosyphon to keep the group warm. However, the Appia uses a proprietary group, designed in the aughts, that has lots of head space and likes larger baskets and doses. It will be more forgiving and produce heavier bodied shots. The Bezzera uses the Brasilia group, designed in the seventies, which has very little headspace, fabulous water distribution, and likes medium sized baskets with low doses and fine grinds. It is a lot more finicky, but can produce amazingly clean shots when all the stars align.
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Randy G.

#3: Post by Randy G. »

Any answer would likely be widely-general at best in terms of value. Like asking, 'Do all cars with Michelin tires handle the same." It is just one part of the puzzle. The HX just gets water hot in a small chamber to avoid brewing with 'stale' water in the larger boiler chamber. Overall boiler design, shower screen, water path, temperature control in the boiler, mass of the group, type of pump and lots more all contribute. And like a sports car, it is more than just the equipment. A good driver adapts to the machine to get the best from it.
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nichikumaat (original poster)

#4: Post by nichikumaat (original poster) »

Well, those two answers enlightened me! Thank you guys!

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#5: Post by EddyQ »

Many HX machines need cooling flushes. My KvdW Indro HX lever needs a warming flush for first shot and no flushes for successive shots. So yeah, different machines matter and it is best to learn what you got.
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#6: Post by Bluenoser »

HX machines control brew water temperature differently than single or dual boilers. And so you will find quite a wide range of characteristics between HX designs. If not familiar, it is helpful to read a bit about how the thermosiphon works (and the influence of the E61 group).

HX designs all use a thermosiphon that circulates future brew water thru a tube in the boiler to the group and back to the boiler. Older designs cycled water quickly, which became very hot and needed a good flush to cool the water before brewing. Somewhat newer designs put a restrictor in the thermosiphon loop (the restrictor is not that new, but newer designs used smaller restrictors). The idea of the restrictor is to slow down the circulation and reduce the temperature of the water near the group. Practically, this means those machines will require less flushing. This may be important for those that lug their own water and don't want to waste lots flushing. But the cost of having a restrictor in the thermosiphon is that it slows down the time for reheating the TS water. This means you might need to wait longer between shots for the machine to get back up to a normal brew water temperature. For this reason, using a group thermometer, like Erics, can tell you when the water is sufficiently reheated. The thermometer can also give you an indication of what your brew water temp actually is. People who are very familiar with their particular HX machine do not need the thermometer, but it can be an asset for newer users.

Restrictors also vary in diameter from about 2mm to 3mm, that I've read about; and different thermosiphon geometries and restrictors give the machines different operating characteristics. In my Pro500, the rebound is slow and I will have to wait about 15 minutes between shot #2 and #3 (back to back). The Appartamento uses a 3mm (I think) and I've read that it rebounds faster, but likely requires a bit longer flush before shots. Even within machines of the same model, you may find slightly differing reheating times as thermosiphons can be finicky.

Originally designed for commercial use, flushing was not an issue (often plumbed in), since baristas were making so many back-to-back drinks that after the initial flush, the water did not overheat as much because of the constant use. A short flush before the shot and the brew water temp was relatively consistent.

A major characteristic of HX designs is that you have to more actively control the brew water temperature through flushing and timing. Manufacturers claim they have solved this by adding a PID, but this is not the case. The PID only controls the temp of the water in the steam boiler. There is zero control by most machines (ie: ECM/Profitec/Rocket) once it leaves that. The MaraX is one of the few that actively changes the steam boiler temp and does actually control the brew water for you.. and I think one of the Bezzera models has an additional heating element in the group that controls the brew water more actively; and there are likely others.

However, most HX machines are designed so the user simply needs to do a small 3-5 second flush, put in the portafilter and pull their shot. It becomes a bit more work if you are using light roasts and/or want a more exact brew water temperature.