WANTED: Volunteer to do a test for me, to help me calibrate my EM6910 pressure gauge

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I would like assistance from someone who has access to an espresso machine that can easily vary the brew pressure, and that can accept the 58mm Sunbeam Cafe Series (e.g EM6910) filter baskets. You can use your own portafilter, but it must be compatible with the Sunbeam filter baskets.

Here is the test:

1. Fit any Sunbeam 58mm Cafe Series DUAL-WALL(pressurised) basket to a machine that can vary the brew pressure accurately. Do not put any grinds in the basket at all.
2. Make sure the machine is set for a constant brew pressure after any ramp-up.
3. Start a shot, and wait for the pressure to stabilise.
4. Once the pressure has stabilised, put a container under the portafilter and start collecting the pour, and at the same time, start a timer on a stopwatch.
5. Time how long it takes to gather 60mL.
6. If it is 16 seconds, report the brew pressure. (end of test)
7. If the time is longer than 16 seconds, empty the container, increase the brew pressure, and go to step 2.
8. If the time is shorter than 16 seconds, empty the container, reduce the brew pressure, and go to step 2.

Greg.

[TC]

Why?

Are you trying to get a feeling of what your gauge does? Gauges vary- a heap.

The only prosumer machine on the market which can vary the brew pressure is the Ambient&spresso Vesuvius. There are 2 of them in the country.

[Skip]

Yes - I want to get a feeling for how my gauge behaves.

Yikes - I had no idea that it was so uncommon to be able to vary the brew pressure!

Do you know whether that Greg Pullman pressure gauge is compatible with the EM6910's portafilter? I have two portafilters - one has a coarse thread for the spouts, and the other has a fine thread.

EDIT: Hang on a minute - it doesn't have to be a prosumer machine - I was envisaging a PROFESSIONAL machine. I want someone who has access to ANY machine that can vary the brew pressure fairly accurately.

Greg.

[Bames]

The other problem is pressure out of the group head does not necessarily correlate to flow. You can have the same pressure - eg 9bar - and get very different amounts of flow depending on how many, how large, and just generally how the flow restrictors in the machine are set up. Unfortunately this test will tell you nothing you can use.

Only way achieve what you are trying to do is get a PF with a pressure gauge on it. Try this - http://coffeesnobs.com.au/brewing-eq...auge-road.html

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Bames: I've thought about it, and I think you are incorrect. A given flow through the filter basket will produce a constant pressure in the filter basket. My test should work. (I know it's not ideal, but it would be a start)

And yes, according to this post, Greg Pullman's pressure gauge will fit the EM6910, which is great! http://coffeesnobs.com.au/brewing-eq...tml#post409265

Going away soon - will send the email to get in the queue for the pressure gauge in a few weeks. (I'd hate to hold others up if it arrives while I'm away)

In the meantime, if someone can do the test, I'd really appreciate it.

Thanks,
Greg.

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Bames: I think I understand what you're saying now. You're saying that the WAY the water flows through the group head and through the basket might affect the resulting pressure? I.e, if it's turbulent, or very even ("laminar"). Any idea roughly what percentage difference this could make? I'm still wondering whether the test is quite as useless as you seem to be implying though. I guess if some kind of mechanical resonance occurred, and the pressure did NOT stabilise at all, then of course it would be pretty useless, unless the average pressure could somehow be ascertained perhaps.

Greg.

[Bames]

Just had a quick look at your other thread asking about this too.

you said in that thread "At the moment I'm a bit puzzled, because in order to produce a 25 second shot for the double (single wall) basket), the pressure gauge has to be a fair bit higher than the centre of the recommended range." This is because without a modification like Pete suggested, you will almost definitely be getting more than 9 bar through your coffee when pulling a shot. I would estimate to get 60 ml in 25-30 seconds from the stock EM6910 single wall basket (which normally holds ~20g of coffee??) your machine will putting about 11 bar through your coffee. True story.

The EM6910 does not have a pressure reducing valve (aka an OPV), so for example when you choke your machine (grind so fine as to get no flow), your coffee will be being hit with around 14-15bar from your 15bar vibe pump.

On a machine like this with no OPV (and installing one would not be worth the effort - trust me I did it on an Oscar), you need to completely forget about hitting a particular pressure. Seriously. Put duct tape over the pressure gauge. I'm not even kidding.

Instead, to get the most out of your machine, manage your grind and dose to achieve tasty espresso. Seriously that's it. Get some digital scales and weigh (ideally down to 0.1 of a gram) as this will allow you maintain a consistent dose. Then change your grind until you get the taste you like. Try 20 seconds, 25, 30 etc.

Also, if you have scales, a more accurate way to measure what comes out is by weight rather than volume (ml). Aim for double the weight of espresso out than ground coffee in as a starting point, and then adjust based on tastiest result.

All the best!

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Bames: Yes, I know it doesn't have an OPV, and everything you say makes perfect sense - thanks. (and I have no trouble believing that 11 bar figure for 60mL in 25-30 seconds, assuming roughly 12 o'clock is 9 bar, which according to a post I saw elsewhere was the case for at least one machine on which a proper gauge had been fitted)

Now if someone could do the test, I'd appreciate it. Chop chop.....

Greg.

[burr]

I think you need to keep in mind what you hope to gain from this. Sure, it will interesting to know what pressure you are extracting at, but how will it help? I have a hard time getting my head around the variables in the system, but I found moving from the sunbeam to a fixed pressure (rotary) machine, changes in the grind had a more dramatic effect on extraction times. With the Sunbeam if you overdosed/ground too fine it would still pump it through, in extreme cases dripping out pure oil! I figure the pressure behind the puck was atleast 13 or so barr. In my rotary or gaggia (OPV) these would simply choke the machine and nothing would come through.

In theory one could adjust dose and grind to get 9 barr shots on the sunbeam, but then the flow rate might be too high giving fast shots? I have a feeling that a nice, syrupy shot on the em6910 is around 10.5 barr. Hah once again complete guesswork.

I'm not having a go at you or anything, I would also love to learn more about how the system works, I'm just not sure how it will help you. Someone like Chris (talkcoffee) would have experience playing around with pressure profiles on prosumer machines and the impact it has, I expect there are more important variables than a 1 bar difference in pressure. I will say though that while my lattes haven't changed much with the new machine, the espressos are significantly better.

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Also, let's say I did stick to Sunbeam's recommendation (ignoring your advice), and tried to keep the pressure in the recommended range (ideally near the centre). Is it possible to produce a relatively fast shot that is roughly equivalent in taste, to a shot that is taken with a higher pressure, but for a longer time?

Greg.

[MrJack]

It's weird. There is very little sensible response in the other thread, and oodles of it here.

All this talk of laminar and turbulent flow... you're not an undergraduate engineering student by chance?

[Pete39]

Still not trying to hit your experiment on the head, but Bames is right - the pressure gauge is a waste of space. The 6910 pressure gauges are notoriously useless. But have fun experimenting. As you say in your other thread, you will learn a lot.

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burr: Sorry - I had replied before noticing your reply. As you can see, I have the same kind of questions you do.

I'm wondering whether the concept of "extraction energy" might be useful for espresso making. I.e - just perhaps, it might be possible to produce a fast high pressure shot that is approximately equivalent to a slow, low pressure shot - in both cases the total ENERGY imparted by the water to the grinds might be the same.........

Greg.

[Skip]

Just do the test someone. This isn't my fault - it's Sunbeam's fault for not including a calibrated pressure gauge.

Greg.

[thewoodensquirrel]

Hi dont mean to but in. I have been playing around with my sunbeam 6910 for years but the only time I got a consistent tasty shot was when I pumped the pressure past sunbeams guidelines