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Earlepap
24-04-12, 03:41
This may be a silly question but when machines have a pre-infusion feature, what exactly does this mean? Does it just run some water into the portafilter before commencing the shot proper?

I presume it must be more complicated than that, since if it's not surely pre-infusion could be attained by just flicking the brew button on and off for a couple seconds before leaving it on for the whole shot - using a machine like the ubiquitous Classic.

MikeHag
24-04-12, 06:28
As I understand it, a 'proper' preinfusion is at low pressure... 1 to 3 bar... just enough to pre-wet and let the grinds expand.

jimbow
24-04-12, 07:51
Basically, like Mike says, I believe it is similar in function to the bloom in brewed coffee. Evenly wetting the grounds prior to extraction means you are more likely to get an even extraction and less likely to get channeling. In fact I remember reading somewhere, for brewed coffee, that grounds that are not wet at the start can become hydrophobic during the main extraction. Pre-infusion in espresso may also sometimes include a steady ramp up to full brewing pressure.

Earlepap
24-04-12, 09:24
Ah right, pressure. Thanks. Why this was troubling me at four in the morning I don't know.

JamesG
24-04-12, 09:30
Scott Rao writes in 'The Professional Barista's Handbook': "Numerous coffee professionals, including me, have found that most forms of preinfusion, on most machines, decrease the incidence of channeling and make the espresso machine more forgiving of flawed distribution, tamping, or grind setting".

As Jimbow and Mike said its a lower pressure wetting, so its a bit different then simply turning the pump on and off quickly on the Classic. Interestingly, the Baby Twin (and I think the Baby Dose) have a preinfusion setting, but its only on the single shot button, not the double or manual button.

seeq
24-04-12, 09:53
I assume a PID with pre infusion attached to a classic just turns on the pump for a second, as I can't see how it could pump at a lower pressure?

garydyke1
24-04-12, 11:28
E61s tend to naturally have pre-infusion as the pressure ramps up. Some machines (including mine ) have additonal preinfusion - water only under no pressure, doesnt engage the pump.

AlIam
24-04-12, 12:02
IIRC, vibe pumps ramp up pressure fairly slowly so presumably the PID switches the pump off long before the pressure reaches 9 bar.

jimbow
24-04-12, 12:43
I believe pre-infusion is one of the reasons stock filter baskets on many machines can hold more than the 14g dose of ground coffee they are designed for. The extra volume provides headroom above the puck allowing the grounds to become wet and the pressure to ramp up gradually, supposedly simulating the pre-infusion in E61 machines with their separate pre-infusion chambers.

Sent from my HTC One X using Tapatalk 2

fatboyslim
24-04-12, 01:40
I assume a PID with pre infusion attached to a classic just turns on the pump for a second, as I can't see how it could pump at a lower pressure?

I have pre-infusion on PID but have yet to see really beneficial results.
The stock settings don't provide a benefit in my opinion. Slightly concerned that it still blasts the puck and actually increases channeling.
Could probably solve this by using a really short pulse time, like 0.7 seconds. Definitely needs more experimentation.

maarten_booij
24-04-12, 09:42
Yeah, pressure is key. I have been experimenting a lot with manual pre-infusion on my classic, and am getting the best results with a couple of second pre-infusion with the steam wand slightly open. This way the pressure is lower and the water that will still come through the head just wets the grinds. Definitely tastes better imo

fatboyslim
25-04-12, 09:10
Yeah, pressure is key. I have been experimenting a lot with manual pre-infusion on my classic, and am getting the best results with a couple of second pre-infusion with the steam wand slightly open. This way the pressure is lower and the water that will still come through the head just wets the grinds. Definitely tastes better imo

You sir are a genius. I remember you saying awhile ago about opening the steam valve and gradually closing to crack up the pressure.
So I combined the PID pre-infuse with your technique, opening valve during pump pulse (about 1.2 seconds) then during the dwell time (about 2 seconds) I closed the valve so when the brewing started it was back up to full pressure.

Definitely seemed like a more even extraction. Thanks Maarten :)

JamesG
25-04-12, 10:39
I second that you are indeed a genius. Just tried the steam wand trick and it works great!

Thanks Maarten