Trouble with new HX espresso machine - please help - Page 4

Beginner and pro baristas share tips and tricks for making espresso.
nuketopia
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#31: Post by nuketopia »

bluesman wrote: Ambient atmospheric pressure is largely and almost certainly irrelevant to making espresso with closed circuit / closed boiler HX machines - including the HX flush - if science is to be believed.

However, ambient pressure *is* relevant to observing the cooling flush to determine when enough flushing is done.

The e61 HX thermosyphon system continuously circulates water between the brewgroup and the heat exchanger in the boiler. The water picks up heat from the boiler, circulates through the e61 brew head and loses heat to the atmosphere. A properly functioning e61 heat exchanger is essentially sealed and it reaches a temperature/pressure equilibrium with little dunnage space in it, and the temperature differential between the heat exchanger (hot) and the e61 brew head (cooler) causes the water to circulate.

Water that is above standard atmospheric pressure can exist as liquid above the standard boiling temperature. For instance, the liquid water in the steam boiler when it is registering 1.4bar is at 230f. The water in the HX/e61 circuit, will approach, but not attain that temperature as it sits in idle, since it is losing a lot of heat through the brew group. (the point of all this water circulating is to keep that hunk of brass warm!!).

As soon as pressurized water is released to lower ambient pressure, it will flash boil to release the excess heat since it can't exist as a liquid anymore. That flash boiling removes heat from the parcel of water, leaving the remainder as liquid. We see this when opening the hot-water tap on an espresso machine to make tea or rinse cups, or when running the cooling flush from the brewhead.

The purpose of the flush is to reduce the temperature of the water in hx/e61 circuit so that it is suitable for brewing coffee. Normally, we want something around 200f.

A long idled e61 will produce water much hotter than that.

It is not the brew process itself that makes much difference in atmospheric pressure - it is what is observed while doing the cooling flush. At sea level, that immediate flash boiling (ie, spitty flow) will quickly smooth at a higher temperature (~212f) than it will in Denver (~203f).

Hence,if two identical e61/hx machines are operated, one at sea level and one in Denver, with the same boiler pressure, ambient temperature and idle time, the Denver one will be spitty longer than the sea level machine. What would be different is when the observer stops the cooling flush. At sea level, one would run the flush longer after "spittiness" stops. In Denver, one would stop the cooling flush shortly after spittiness ceases.

In all likelyhood, the time period would probably be about the same as would the volume/mass of the flushing charge.

Again, it isn't the brew cycle that is relevant, it is the observation of the cooling flush.

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aecletec
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#32: Post by aecletec »

The puck and basket are permeable, though, so it's not a true seal. There is also an air gap between the puck and hx valve which will be at atmospheric pressure. This seems like it'd have an effect on the water behaviour.

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homeburrero
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#33: Post by homeburrero »

bluesman wrote:As soon as you lock in the PF you seal the brew path and isolate the water from atmospheric pressure.
aecletec wrote:The puck and basket are permeable, though, so it's not a true seal.
This thread is getting terribly confused by misunderstanding that the basic point here is about the effect of altitude when using the common technique of timing the cooling flush based on the end of the water dance. No puck, and no portafilter are in the picture here.

I think nuketopia has explained it perfectly well twice now, and the physics is really not at all complicated. I'll give it a try again with a specific example:

Consider identical machines in Denver and in Houston, both starting a cooling flush at the same time.
  • - at 2 seconds, water/steam is flowing from the shower at 215F on both machines, 15 ml total has been pumped
    - at 8 seconds, water/steam is flowing from the shower at 211F on both machines, and 60 ml total has been pumped. In Houston the 'water dance' has just ended, and the stream is pretty much pure water.
    - at 16 seconds, water/steam is flowing from the shower at 202F on both machines, 120 ml total has been pumped . In Denver the 'water dance' has just ended.
Note that in terms of flush time and water pumped, the machines at the different altitudes do indeed behave the same. However, if you use the common practice of counting seconds after the end of the water dance, a count of 9 Mississippi in Houston is equivalent to 1 Mississippi in Denver. Of course if you used an EricS thermometer to stop the flush, altitude would make no difference. If you used the volume of water in a container under the group to decide the end of the flush, you would need to use a somewhat smaller volume in Denver than in Houston (because more of the flush water will be lost to vapor at the higher altitude.)
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

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bluesman
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#34: Post by bluesman »

aecletec wrote:The puck and basket are permeable, though, so it's not a true seal. There is also an air gap between the puck and hx valve which will be at atmospheric pressure. This seems like it'd have an effect on the water behaviour.
If it can hold 9 bar with the pump running, atmospheric pressure will not affect what's going on inside.

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bluesman
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#35: Post by bluesman »

homeburrero wrote:This thread is getting terribly confused by misunderstanding that the basic point here is about the effect of altitude when using the common technique of timing the cooling flush based on the end of the water dance...Consider identical machines in Denver and in Houston, both starting a cooling flush at the same time.
  • - at 2 seconds, water/steam is flowing from the shower at 215F on both machines, 15 ml total has been pumped
    - at 8 seconds, water/steam is flowing from the shower at 211F on both machines, and 60 ml total has been pumped. In Houston the 'water dance' has just ended, and the stream is pretty much pure water.
    - at 16 seconds, water/steam is flowing from the shower at 202F on both machines, 120 ml total has been pumped . In Denver the 'water dance' has just ended.
Has anybody actually done this to see if it's correct? What I know of the science behind it suggests to me that it is not what would happen. I doubt that the vaporization of a few ml of water at 203 would even be visible compared to the explosive discharge of the pressurized steam already in the HX. When that's vented, the water will look calm in comparison despite some minor vaporization - and it will take no longer in Denver than it will in New Orleans.

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aecletec
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#36: Post by aecletec »

Yes, testing is probably what's needed to settle this... I think otherwise we'll quibble about details! Too many threads have gone down that path ;)

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homeburrero
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#37: Post by homeburrero »

bluesman wrote:I doubt that the vaporization of a few ml of water at 203 would even be visible compared to the explosive discharge of the pressurized steam already in the HX.
Do the math and I think you'll change your mind about that. Only 3 ml of water, when vaporized, will become nearly 4 liters of steam. Huge when compared to any steam that may or may not be in the HX.

And I'm not convinced that there is much steam in my HX. It needs to be nearly all liquid water, because if it gets vapor or air in it the thermosyphon stalls. When my pump (rotary) kicks on in a flush, my gicleur causes the pressure in the HX to hit to about 8 bar, so I'm pretty sure that if I did have any vapor in the HX it's condensed back to liquid when I start flushing.

I do have an indication of the temp of the water flowing past my EricS thermometer (which is in the path, after the gicleur and above the screen) and it quickly hits 210 - 215F. Then gradually declines. The flash boiling declines gradually along with the declining temps, becoming smooth and calm after the temps go below local boiling point.

Here's a graph of actual group thermocouple data showing some flushes at a few different pstat (boiler temp) settings: Erics e61 adapter, how to pull consecutive shots?

And finally, my initial advice to to the OP in Denver on this thread was based on experience with my machine in Albuquerque, along with what I've learned from posts to this forum. If I tried to do 6-8 Mississippi past the water dance here, as some E61 experts advise for sea level, my shot would be way too cold. And when I need to try a relatively hot shot, I have learned to stop the flush before the water dance ends and let it rebound a bit. I did a lot of that recently when trying to review a coffee with a recommended brew temp of 204F.
Pat
nínádiishʼnahgo gohwééh náshdlį́į́h

DeGaulle
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#38: Post by DeGaulle »

One of the reasons for a cooling flush is to avoid a burnt taste of your brew. The discussion about brewing at altitude made me wonder whether the coffeepuck gets scalded by water that is too hot or by flash steam that condenses and releases latent Heat onto the puck when the pump is first engaged. From homeburrero's comments about the flush-and-wait-for-rebound I gather that a slight rebound after you have flushed only just to the end of water dance does not adversely affect the taste when you do this at altitude. So would it be fair to say that it is overheated brew water that scalds the coffee rather than flash steam that could be released as soon as the brew temperature rebounds past the atmospheric boiling point ?
Bert

Deebo (original poster)
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#39: Post by Deebo (original poster) »

You know, I have tried changing everything I possibly can, but all of my shots have this lasting aftertaste that is just awful, its dry and sits on your tongue, almost metallic. I've even changed blends and its the same thing.

The shot coming out of he machine looks great, but no matter how long I flush it for I can't get this to go away. I've read and re-read the diagnosing page but I just can't figure this out.

Its a little discouraging to have been pulling much tastier shots on a $600 machine... I'm sure the rocket is capable but Im running out of ideas here.
Think it, but don't overthink it...

DeGaulle
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#40: Post by DeGaulle »

Have you tried adjusting a coarser grind? A dry aftertaste suggests overextraction. Does it improve If you grind slightly coarser and thus speed up the flow rate, keeping all else equal (dose, flush till end of water dance etc.) ?
Bert