min VII Now Always blonds? Every shot

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JohnH

min VII Now Always blonds? Every shot

Post by JohnH »

My 3 1/2 year old mini VII always wants to blond every shot now. I've tried everything. Yes, using fresh (6-7 day old) coffee. Has pre-infusion. Offset originally set by Chris's Coffee at +4. Tried short shots, fine grinds, increase a degree or two, different coffees, (lasts CC Apollo)etc. etc. Still blonds everything and is slightly sour. Never used to do this. Is temperature way off? Any ideas out there? Many thanks.
richardcoffee
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Re: min VII Now Always blonds? Every shot

Post by richardcoffee »

Usually this kind of problem is the fault of the grinder. What are you using? Have you recently cleaned the grinder? How about new burrs?
JohnH

Re: min VII Now Always blonds? Every shot

Post by JohnH »

Wish that were it. Fairly new Mazzer Mini E Type A. Works great and has in the past.
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chas
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Re: min VII Now Always blonds? Every shot

Post by chas »

If you want to verify that your brew temp and offset are correct the only real solution to use a 53mm Scace device plus digital thermometer. You can rent one for a couple of weeks - assuming he still offers that service. PM "sakurama" and ask. If he doesn't respond, PM me and I'll give you his real name and e-mail address.

Since a new one costs $302, you have to provide your own bottomless PF and digital thermometer, AND there is a 6 week lead time, renting the entire thing from sakurama is the way to go.
Chas
LM GS/3 & LaSpaziale Dream v 1.25 (US 120V)
Mazzer Kony E, Customized Rocky
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chas
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Joined: Wed Jun 02, 2004 11:52 pm
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Re: min VII Now Always blonds? Every shot

Post by chas »

Have you also checked your brew pressure using a blind basket and the built-in pressure gauge? It should be at least 9 bar in this case. However, that is not entirely accurate. The pressure gauge picks off at the output of the pump. When you are drawing water at the rate of ~2oz in 25 sec, there is actually a pressure drop between the pump and the top of your coffee bed. This is on the order of 0.5-1bar. So if you use a blind basket to set the pressure you should probably set it 0.5-1bar higher than you want it to be at the top of the packed portafilter.

The only totally accurate way to do this on an S1 class machine is to use an old 53mm portafilter and build your own PF pressure gauge. You can buy gauges that screw right onto the thread of the portafilter. However, if you only do that you'll get the same reading as you get on the built -in gauge. What you need to do is a bit of plumbing. You need to add a needle valve as well which has been adjusted to let out 2oz in 25 seconds or whatever you desire your flow and interval to be. Folks on this forum have built these and posted photos.

Here is one. I am not sure from the photo if this one includes the needle valve. One thing that you can do instead of installing a needle valve is drill a very small hole in the end cap.

viewtopic.php?f=57&t=1125&p=13701&hilit ... uge#p13701
Chas
LM GS/3 & LaSpaziale Dream v 1.25 (US 120V)
Mazzer Kony E, Customized Rocky
Hottop P/B
JohnH

Re: min VII Now Always blonds? Every shot

Post by JohnH »

Thanks, Chas.
Pump pressure was vacillating between 8.5 and 10. Chris's Coffee had me LOWER the pump pressure to increase extraction time which seemed to work at first, however, now it seems to choke the machine with a reasonable grind and not enough pump pressure. Suspect that the problem is either the vibe pump or the brew temp as you note and will have to decide how to proceed on some of the solutions you suggest. Wish the gauge on this machine was a little better and positioned better.

Can you PM me with your thoughts on the La Marzocco and why you decided to acquire it when you have a Vivaldi Dream? Meanwhile I will reset the pump pressure back up.
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