Kipp wrote:It is without a doubt easier to pull a great shot with lower pressure.

You do loose creama and mouthfeel/body with lower pressure, but by lowering the water debit to 250ml/30 sec or so with no PF you will get the mouthfeel/body back.

Lower pressure will certainly be more forgiving. And in that sense easier to pull a good shot.

But in terms of body/mouthfeel, the 8.5-9bar is probably going to give you max body/mouthfeel - if you're able to adjust your grinder to allow it.

In term of the other settings, I actually haven't read Michaels article yet (I know I know it's on the list) but I've pretty much come-to identical conclusions with my EK. Although I do some things slightly differently. Such as water temp, dose and and grooming (but all with similar reasoning in mind).

nickw wrote:

In term of the other settings, I actually haven't read Michaels article yet (I know I know it's on the list)

Ah Nick, it's a MUST read!

Best article of the Year!

Without doubt it's a great read that covers lots of the details involved in pulling low pressure shots. Still, the article describes a very specific setup that can't be easily reproduced by every home barista. So what of it can be applied in general? Is 6 bar the new standard for everybody?

In my opinion it seems to be the question wether it is worth sacrificing a bit of the fantastic body/mouthfeel the big conicals offer for more forgivingness, sweetness and balance. As I'm still waiting for my K10 to arrive I was not yet able to try myself.

nickw wrote:It depends on the type of grinder you're using,
When using a brew grinder like the EK43 you don't create enough fines to hold the water back. .

From Matt Perger B.H. http://www.baristahustle.com/the-ek43-part-two/

- 4 -
The EK43 is making the most fines (gasp!) but I have two things to say to this.
1. The EK43 is slicing each coffee bean so many more times than the other grinders; it's a super small grind size. With this in mind, there should be much more fines; but there isn't. It's only producing 3% more 0-90um particles than the Robur. It's doing an admirable job of hitting such a fine grind and producing so few fines.
2. The rest of the grinds are so much closer to the fines than with the other grinders. As I'll explain later, this is one of the defining factors in the EK43's superiority.

Kipp wrote: Your grind will be much finer which will help it to be more unimodal even with non Mythos or EK grinders. You will see this with a naked portafilter as less striping and a more solid, uniform color.

Here is a vid that shows this to be true. https://www.youtube.com/watch?v=v-r_XAip5RM

This is an interesting observation as it proves that if there is a tight particle distribution that all particles are extracting at the same rate and the shot will be all one color; and tiger striping indicates that some particles are extracting faster than others.

a traditional espresso grinder, hence bimodal, makes more fines at finer grind setting; that is, the narrower distributions are at coarser grind settings; also, they say, a conical grinder makes more fines, so it is... more bimodal, than a flat one;

and no matters how unimodal the grind is, in my understanding, there will be into the puck, layers of different extracting rate; because the extraction water in its flow vertically into the puck will become more and more saturated with solubiles and will extract less from the inferior layers; and the layer of maximum extraction is descending dynamically through the time of extraction;

also, if blends are used, it is quite a challenge to have the same solubility for all the particles of the same size; it comes to the skills of the roaster and the blender...
so, IMO, unimodal grinding and the same solubility for the same particle size of the blend components, could improve the extraction rate, but the particles into the puck will not extract at the same rate;

anyway, I leave the truth into the hands of more experienced people, with high-end machines and lab testing facilities;
for me, a nice tiger stripped flow from the naked PF with some normal blend (roasted by me), is the best I can have

I've been playing with reduced pressure lately. But I can't say the experimentation has been rigorous. My issue is I have an E61 HX with a vibe pump. While I do have a brew pressure gauge... without a Scace to confirm, I don't know my actual brew pressure.

I've read that vibe pumps can actually be 2 bar lower in the group than with a blind filter. But I have no way of confirming this.

For the longest time I had mine set to 9 bar against a blind filter. But that left me wondering if that really meant 7 bar during brew. I was always mostly happy with my shots at this setting, whatever it actually is in reality.

Then this revisited low pressure paradigm came along and I reduced my pump even further to 8 bar blind. The thinking is that this would be 6 bar for brew. But I have no idea what my precise brew pressure is, other than what my gauge is telling me.

Anyway, the lower pressure seems to help with light roasts. I'm getting fuller, sweeter extractions and can run the shot longer without increased bitterness. This is grinding with both my K10PB and Vario.

Can anyone definitively confirm the actual pressure offset that exists for vibe pumps on E61 machines? Is there really a 2 bar differential? Or is every machine different depending on how it's set up?

canuckcoffeeguy wrote:
Can anyone definitively confirm the actual pressure offset that exists for vibe pumps on E61 machines? Is there really a 2 bar differential? Or is every machine different depending on how it's set up?

The actual brew pressure will depend on the resistance of the coffee puck itself.

The SCACE device has a calibrated orifice that simulates the water flow through the puck by restricting it.

In most machines the water flow is:

Pump -> T -> HX or brew boiler -> restrictor -> shower screen

The pressure gauge is usually situated at a "T" fitting at the input of the HX or the brew boiler, or on the tube leading from there into the e61 type brewgroup.

So brew gauge reads the pressure ahead of the restrictor. The actual brew pressure is a product of the water flow through the restrictor and whatever resistance the puck offers to the water flow. It will always be less than the gauge *if* there is any water flow. If you put in a blind disk (like for backflushing) the pressure will equalize since there's no flow.

Most people seem to estimate that there's about 1-bar difference between the pressure gauge when measured with a blind disk and actual brewing conditions.

The best way is to measure with a SCACE, and even that is a simulation of actual conditions.

Just to clarify and simplify, the 6 bar pressure stated in "Low Pressure Rehash" article was the pressure shown on the gauge of La Marzocco machines while pulling an actual shot.

Much cheaper than a scace could be to build your own portafilter pressure gauge with needle valve, and set the needle valve to your desired flow rate.

Here is an old thread with some examples: Building a Portafilter Pressure Gauge

I have built one myself, they are relatively straightforward to build and rather useful.