What makes the steam from some espresso machines drier than others?

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#1: Post by boren »

The steam from my Elektra Microcasa a Leva is very dry. I can steam 150 ml of milk without purging the wand first, and it only adds 15 ml of water. Whereas with the Quick Mill Alexia EVO (an E61 single-boiler machine) I need to purge at least 100 ml of water to even get steam that I consider suitable for the job. Steaming the milk then adds 30 ml more. In total that's 130 ml with the QM vs just 15 ml with the MCaL.

Any idea what's the technical difference for such huge differences in steam "dryness"?

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#2: Post by JRising »

If you're talking about traditional boilers, mostly, it's the temperature of the steam leaving the tip.
Think of what steam is, it's water. It is heated to above boiling point and contained in a boiler under pressure. When a valve is opened to let it escape, it rushes out to atmosphere. If it isn't well above boiling in the boiler, then it'll have lost all that energy by the time it passes the steam tip and will be spitty.
While in the boiler it is pretty much a constant temperature, the same temperature as the liquid in the boiler, it is packed full of energy because the element put so much heat into it. As it rushes out from the boiler (At maybe 1.2 Bar) toward your pitcher of milk at 0 Bar it is expanding and losing energy rapidly. As it passes through restrictions like the valve and ball joint it undergoes a substantial pressure drop at each restriction until the final restriction of the steam tip.
So long as the steam tip is a much more significant restriction (say a 0.9mm single hole) then the other restrictions become somewhat irrelevant, but try opening your steam valve so slightly that it becomes a significant restriction you'll see the steam from the tip is burping out a lot of liquid water. Picture the steam passing the nearly closed valve, the steam wand downstream is at almost 0 Bar because the steam tip is open to atmosphere, so the steam does most of it's expanding in the steam wand, and plenty is free to condense back to water at the steam tip and be blown out wet with the flow. Keep your steam valve, ball-joint, wand-lining on a burnless, etc. clean for drier steam.

For non traditional boilers, steam generators/thermal blocks... Machines where the pump goes Thump... Thump... Thump... The heating element has to be putting heat into the thermoblck at so much power that every pump stroke of water coming in heats to enough above boiling temp that it is still dry by the time it gets to the end of the steam wand. If there's calcium in the thermoblock, it is insulating the water and the water might not be well above boiling by the end. If the pump is thump thump thumping too fast, it may be providing more water than the element is providing heat for and same wet result. A significant restriction before the steam tip could do the same as it does for a traditional boiler.

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#3: Post by HB »

It sounds like the steam boiler water level for your Alexia is too high. Since it's a single boiler, there's no real option other than purging water. With the Microcasa, you can precisely set the steam boiler water level simply by not overfilling it. If I'm making just 1 or 2 cappuccinos, there's no need to fill the Microcasa's steam boiler beyond half full, which means super dry steam.
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#4: Post by walr00s »

Chris' Coffee advised me to purge water through the group by putting the lever in the middle position to clear more liquid out of the boiler before I begin steaming (while in steaming mode). This helped some with the inconsistency I experienced in terms of steaming.

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#5: Post by MTN Gert »

I think this is why the Eagle one prima has such dry steam. It runs at 2.2-2.5bar which makes the water so hot that the steam has not lost enough temp or pressure by the time it exits the steam wand to turn back into water.

My Brasilia Portafino DEL-1 commercial espresso machine has very dry steam also but that is probably because of the massive amount of energy stored in a 5L+ boiler at 1.3 bar
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#6: Post by HB »

Higher steam pressure and boiler size doesn't hurt, but it's certainly not required. My Elektra Microcasa a Leva has a small boiler and wonderfully dry steam at ~1.0 bar.
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#7: Post by EddyQ »

My guess is simply the piping and solenoid in the Alexia is a lot of cold metal that must be heated to boiler temperature before you will get the dry steam to the tip.
Also remember that depressurization of gases results in cooling. So you might have some of those differences as well.
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#8: Post by boren (original poster) »

Thanks for all the replies, but I don't think boiler temperature has much to do with the difference. My Quick Mill produces roughly the same amount of water when I steam at 120c and at 135c. In both cases it's about 100 ml of water that I need to purge or it all goes into the milk.

With the MCaL on the other hand the machine is set to 1.0 bar (equivalent to about 120c) and there's hardly any water in the steam. It's a good thing I don't have to rely on the Quick Mill for steaming. I guess it's a nice backup if my MCaL needs to be serviced, but definitely not something that can be considered a good feature (not to mention the 2 minute wait time between brewing and steaming).

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#9: Post by baldheadracing »

The factors are the length, mass, and idle temperature of the plumbing from the boiler to the wand tip. The Elektra has very little compared to the Alexia. Compare the idle temperature of the valve on your Alexia to the Elektra.

Thus, if you first pull enough steam through the Alexia to warm up the plumbing, then you will get similarly dry steam from both machines.
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#10: Post by pizzaman383 »

When steaming, the water in the boiler converts to steam and that process can be frothy and chaotic. This can cause water to reach the steam outlet. As mentioned above, keeping the water level low enough to reduce or eliminate this makes a big difference to the steam's dryness after the steam wand is up to temperature.
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