Tamp pressure and brew pressure

#1: Post by **rotuts** » August 8th, 2009, 10:43 am

I have a new system, upgrading from a Silvia/Solis to the Alexia PID and K3 Doserless.

although its taken me a while to get back to very very good espresso, mostly with a new curved tamper and adjusting the grind, currently I find that my flat steel tamper works better for me.

Ive noticed that with the Alexia there is a pressure monitor on the machine that tells me the pressure while im extracting.

Ive also read here and elsewhere that about 9 atm is about right for the 'best' extraction. therefore does it follow that if my extraction pressure goes to 10 or 11 atm im tamping too hard?

the extraction at 10 - 11 with the bottomless PF looks good and I stop before blonding.

what does 'higher' extraction pressure produce in the cup?

many thanks for so much help!

#2: Post by **another_jim** » August 8th, 2009, 12:37 pm

The brew pressure is not determined by how you tamp. It is determined by how much water is being pumped (more water, less pressure), and the setting of the OPV (over pressure valve). If there is no OPV, the flow for a normal double will run at about 10 bar, for a single, around 12 to 13 bar. At 9 bar, you'll be getting around 3 ounces int the cup. If there is an OPV, it limits the maximum pressure, by opening up and dumping water back into the tank whenever its threshold pressure is exceeded. Italian manufacturers typically set vibe pumps to 11 bar and rotary pumps to 9 bar.

Your brew pressure is based on this OPV setting. If you want it to change, you need to adjust the OPV. Use the search function to find out how; there are lots of posts describing it.

#3: Post by HB » August 8th, 2009, 2:41 pm

rotuts wrote:what does 'higher' extraction pressure produce in the cup?

Generally speaking, higher pressure means more crema, but risks extracting sharper, bitter flavors. I recommend starting around 8.5 bar and adjusting by taste. You can read the specifics in OPV adjustment question - QuickMill Alexia. Here's a photo of the valve in question:

From Buyer's Guide to the Quick Mill Alexia

For the truly curious, see The importance of brew pressure, purpose of adjusting OPV?, I still don't get it: Why adjust the OPV? and more from the FAQs and Favorites.

August 8th, 2009, 3:17 pm

many thanks!

as an addendum, it seems i can go from 9 to 11 or so and the 'green' area on the read out is 9 - 10.

some of my shots have been about 9, some up to 11. within that range, it can only be my tamp, no?

thanks again!

#5: Post by **another_jim** » August 8th, 2009, 4:48 pm

I'm guessing you are not using a bottomless PF.

August 8th, 2009, 4:54 pm

I actually use both. my 'bottom-less' shots have improved dramatically with the 'Weiss' (sp?) technique

but what Im really wondering with the parameters Ive mentioned, 9 bar to 11 bar can only be both the fine-ness of the grind and how hard I compress the 'puck'?

Im very fortunate to move up to the Alexia PID and the K3 and its a great deal of fun and interest to move to the 'next' level

thanks for all the help from Here!

#7: Post by HB » August 8th, 2009, 6:27 pm

rotuts wrote:but what Im really wondering with the parameters Ive mentioned, 9 bar to 11 bar can only be both the fine-ness of the grind and how hard I compress the 'puck'?

In my experience, how you tamp makes little difference in the extraction; a really firm tamp may delay the puck wetting for a few moments longer than a light tamp. If there's a measurable difference the tamp pressure has on the brew pressure, I've never noticed. *shrug*

August 9th, 2009, 12:31 pm

what you mention is very interesting. but wouldnt a very hard tamp need higher pressure to let the water pass through?

if Im looking for 9 bar, and i go up to 11 should I 'adjust down' ?

thanks again for your ideas.

http://users.rcn.com/erics/ · #9: Post by **erics** » August 9th, 2009, 1:10 pm

I would stick a blind filter in the PF and see what pressure reading I get. Repeat this after a 15 minute break just to check consistency and record the value. After another 15 minutes, brew a double shot and make some notes as to taste.

If the blind filter pressure was in the vicinity of 11 bar, run that test again and reduce the pressure to 9 bar. Now run the taste test again, adjusting your grinder as necessary to keep the shot volume/time as consistent as possible.

Tamping the grounds after some reasonable distribution presents a more uniform bed of coffee to the water and ALSO moves the coffee out of the way of the dispersion screen.

Does your Alexia have the relay that knocks out the heating element when the machine is brewing?

August 9th, 2009, 1:13 pm

I can't say if the Alexia has the relay you mention. it does have the PID and thats set to 200

if I get this correct: using the blind PF and checking the max pressure tell me the set for the bleeding of water back into the tank?

very interesting and useful to know

many thanks for all these tips

pls stay tuned and Ill report back soon

the 11 bar shot I had this AM tasted fine to me, BTW

maybe Im not a 'prime taster'