kevinpeters Senior Member Joined: 20 Dec 2012 Posts: 6 Location: Peterborough, Ontario, Canada Expertise: I love coffee
Espresso: Bezzera BZ09 Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 9:17am Subject: Optimal pressure for good extraction?
Hi, This is my first post, although I have read a number of them in the past. I have a Bezzera BZ09 single boiler machine. I think the water comes out too fast for my machine because in order to get a single or double shot in 25ish seconds, the bar pressure reading on the machine hovers around 12. I keep reading that 9 bars of pressure is optimal for good extraction. I have tried a courser grind, and when the bar pressure reads around 9, the shot is complete in less than 15 seconds (i.e., the coffee comes out too fast and is on the sour side). I appreciate that perhaps the pressure gauge on my machine might not be perfect, but I am curious if anyone on this site has had similar issues. I am usually able to get a nice shot with crema, but there is no tiger-striping to the crema that I have seen before. I would be grateful for any tips.
cuznvin Senior Member Joined: 6 Oct 2011 Posts: 417 Location: NY Expertise: I love coffee
Posted Thu Dec 20, 2012, 10:12am Subject: Re: Optimal pressure for good extraction?
kevinpeters Said:
Hi, This is my first post, although I have read a number of them in the past. I have a Bezzera BZ09 single boiler machine. I think the water comes out too fast for my machine because in order to get a single or double shot in 25ish seconds, the bar pressure reading on the machine hovers around 12. I keep reading that 9 bars of pressure is optimal for good extraction. I have tried a courser grind, and when the bar pressure reads around 9, the shot is complete in less than 15 seconds (i.e., the coffee comes out too fast and is on the sour side). I appreciate that perhaps the pressure gauge on my machine might not be perfect, but I am curious if anyone on this site has had similar issues. I am usually able to get a nice shot with crema, but there is no tiger-striping to the crema that I have seen before. I would be grateful for any tips.
I havent pulled a shot yet but from what I gather from endless reading is that if the "pull" is too quick, you need to grind finer, not coarser. Also, what kind of grinder are you using and are you using freshly roasted coffee?
kevinpeters Senior Member Joined: 20 Dec 2012 Posts: 6 Location: Peterborough, Ontario, Canada Expertise: I love coffee
Espresso: Bezzera BZ09 Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 11:12am Subject: Re: Optimal pressure for good extraction?
Hi Cuznvin, Thanks for your reply. I have a Compak K3 touch grinder. I think you are right in that normally I would need to use a finer grind if the pull is too quick. However, the burrs on my grinder are pretty much touching at my setting right now, and if I go any finer, the machine chokes. The only way that I can get the coffee pressure gauge down in the 9-10 range is to use a coarser grind, but then the coffee comes out even faster! Maybe that is just the way my machine is set up. It's not like I am suffering...the espresso is still good. I was just curious if I could make it better.
Posted Thu Dec 20, 2012, 11:26am Subject: Re: Optimal pressure for good extraction?
The over-pressure valve in the machine should limit the pressure at the puck to about 9 bar when there is water flowing at the correct rate. This usually means setting it to open at somewhere around 10 bar static (for a basic vibe pump).
Lowering the OPV setting to 10 bar static on my Gaggia Classic made a big difference to the amount of crema I was getting and made it easier to get a good extraction, with less channelling. I've not measured the pressure in my BZ07, but I suspect it's about right.
If you install a blind basket and pull a shot, what pressure does your gauge show? If it's up around 15 bar, then I suspect your OPV isn't opening. If it's around 12 bar, then it probably just needs adjusting down a bit.
This discussion should help, and the OPV is the part marked TAV. 2 on page 11 of this document (and described on page 5).
calblacksmith Moderator Joined: 25 Nov 2007 Posts: 5,680 Location: Riverside, Ca, U.S.A. Expertise: I live coffee
Espresso: ECM Veneziano A1 Grinder: Many different commercial Vac Pot: 40s era Silex Drip: Milita, Bunn&Curtis... Roaster: Cast iron pan, gas burner
Posted Thu Dec 20, 2012, 2:20pm Subject: Re: Optimal pressure for good extraction?
Something else to think about is that the pressure gauges can and do loos their calibration. You really don't know what your pressure is until you test the system with an external gauge that you know to be accurate. Just adjust the grinder to get good shots and unless you have a reason to suspect that there is a major problem with the machine for other reasons, I would not worry about it until you can test with a known good gauge.
In real life, my name is Wayne P.
Feed the newbs, starve the trolls and above all enjoy what you drink!
kevinpeters Senior Member Joined: 20 Dec 2012 Posts: 6 Location: Peterborough, Ontario, Canada Expertise: I love coffee
Espresso: Bezzera BZ09 Grinder: Compak K4 Touch
Posted Thu Dec 20, 2012, 4:17pm Subject: Re: Optimal pressure for good extraction?
Thanks calblacksmith - something to think about! I would also want to verify that tinkering around inside the machine will not void the warranty before doing anything major.
Posted Thu Dec 20, 2012, 6:07pm Subject: Re: Optimal pressure for good extraction?
Your pressure numbers are textbook for factory settings with a vibe pump. I would suggest you dial down to get around 9.5 bar during your typical shot(actual brew pressure is usually a bit lower depending on gauge placement). See how that works for your shot taste and timing. IMO, dialing in a shot at 11 bar pressure is a waste of time and coffee.
Symbols: = New Posts since your last visit = No New Posts since last visit = Newest post
Forum Rules: No profanity, illegal acts or personal attacks will be tolerated in these discussion boards. No commercial posting of any nature will be tolerated; only private sales by private individuals, in the "Buy and Sell" forum. No cross posting allowed - do not post your topic to more than one forum, nor repost a topic to the same forum. Who Can Read The Forum? Anyone can read posts in these discussion boards. Who Can Post New Topics? Any registered CoffeeGeek member can post new topics. Who Can Post Replies? Any registered CoffeeGeek member can post replies. Can Photos be posted? Anyone can post photos in their new topics or replies. Who can change or delete posts? Any CoffeeGeek member can edit their own posts. Only moderators can delete posts. Probationary Period: If you are a new signup for CoffeeGeek, you cannot promote, endorse, criticise or otherwise post an unsolicited endorsement for any company, product or service in your first five postings.
= No New Posts since last visit 