So I've just received my GS/3 and Mazzer Mini (yay!) - and basically we are pretty sure we have the grind, tamping pressure and the flow right - but we're wondering about the temperature and the preinfusion and how that would affect everything - we are using a central and south american blend of beans, which my friend uses in her coffee bar with a faema due, with great success - on our machine though the shots range from slightly flat, some ashy, other a bit zingy - nothing spectacular, a couple close - shots were originally a little sour but we bumped the temperature up to 203 (from the 197.6 the machine was set to), and we're back down to 201 - 201.5. The water we are using is bottles "natural spring water" as our tapwater is ultra hard with somewhat dangerous levels of uranium!

We would appreciate any advice re the preinfusion - length of time on and off for a single and double shot - and the temperature for this type of bean. I've read many of the posts elsewhere, but would appreciate any advice.

Incidentally, the PID setting is 20F - is this anything to be concerned about - assumed its just the factory setting.

Thanks (in advance), Jonathan & Cindi

chelseacoffee wrote:We would appreciate any advice re the preinfusion - length of time on and off for a single and double shot - and the temperature for this type of bean. I've read many of the posts elsewhere, but would appreciate any advice.

The effectiveness of the GS3's preinfusion has been questioned a few times, most recently on CoffeeGeek GS3 and Pre Infusion. My own brief experience echoes roblumba's report - not a big deal. As for temperature, 201F is a good starting point, then adjust to taste. The range of taste defects you report (flat, ashy, a little sour, etc.) suggests you're too early in your experimentation to really offer concrete suggestions other than "keep trying" and "check the how tos" (especially The Home Barista's Guide to Espresso).

Fueled from the release of the new GS3 paddle group version (at least there's a 220V version out) I started searching on the topic. And there still seems to be quite a bit of confusion out there on how it actually works.
What seems indisputed is, that you can gradually increase the brew pressure from zero to line pressure - what is done at the start of the extraction - by gradually opening a mechanical valve. And then you can start the pump which lets the pressure rise pretty quick to the full value determined by the setting on the rotary pump (usually around 9bars).
Though what can be done with the brew pressure towards the end of the extraction is not quite clear to me.
A 'Marshall' (don't know if it's the same one as the HB-user) asked the following question on flickr - here:

Can you reduce the pressure at the end of the shot, like the Slayer? If you can do so, then can you do gradually reduce pressure, or is it an immediate change from pump to line pressure?

to which the poster replied:

yes, you can gradually ramp up the pressure and at the and ramp it down again.
the valve works is NOT a close/open valve, but one that gradually opens up the flow rate.

I thought that as soon as you stop the pump (by shifting the paddle) the brew pressure would drop very rapid to line pressure again. And afterwards you could slow down the flow rate, by further shifting the paddle and thereby starting to close the mechanical valve again. But his answer suggests more that you could gradually reduce the pressure from its full value down to the line pressure value. Could anyone help me out here please?

grüess marco

I have two questions to this topic;
Q1: From the discussion here, here that there are no point in using pre-infusion with a GS/3 where the water if the machine is drawing water the water from a reservoir (not plumbed)? I suppose the water pressure is higher when the machine is connected to the waterline, but the pre-infusion does still have an effect?

Q2: On my GS/3 i have a timer telling me how long time the pump has been open, but the timer starts when the pump have started, not then the pre-infusion has started (and water introduced to the coffee). It sound strange because the 25 sec. rule is there to stop extraction of elements in the coffee due to exposure to water.

- Espen

A1. Judging from the first page of this thread, it depends on who you ask. In my limited experience with the reservoir-equipped GS/3, I thought a few seconds of "pump-pulse" time seemed to improve the forgiveness factor ever-so-slightly (opinions of experienced GS/3 owners are welcome).

A2. Most agree "pump on" denotes the start of the extracting timing. See When do you start to time the shot? for recent discussion.

Just a quick note for preinfusion for the GS3. The GS3 was designed so that even while using the reservoir option you still have low pressure pre-infusion while the pump is off. There is a small bypass in the mixing valve that allows the coffee boiler to "see" the steam boiler pressure when the pump is off. This means that while the pump is off during the preinfusion delay, the coffee is actually seeing the pressure of the steam boiler. Hopefully 2 Bar in most cases. While it is not quite line pressure (in most of the world) it is a small pressure to keep the water flowing through the coffee and not back through the 3 way valve.



BillC

what does "more forgiving" mean? i don't know what that means (...anymore... i thought i did but no longer.)

HB: thanks for the answer below.

Forgiving = more tolerant of errors in barista technique (e.g., unequal distribution, canted tamp) = less likely to channel.