Every time I try to do a dark roast in my Vac-pot it stalls! 
It is a vintage corey pot that is all glass (glass stopper) no plastic. 

Could someone explain why? 

Thanks 

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Without being there and seeing all of the different aspects of what yhou are doing it's going to be very difficult for anyone to diagnose what's going on.

Grind
Dose
Technique
Dwell Time
Temperature of water going north
Temperature of water when it starts heading south

All things we'd need.

-bry
Bryan

Grind, dose, temp, dwell time, techniques, temp is all consistent & it never fails with a medium or light roast!
But a dark roast will stall more often than not.
Is it oily grinds or lighter grinds? I just can't figure it out!




Bryan Wray said:
Without being there and seeing all of the different aspects of what yhou are doing it's going to be very difficult for anyone to diagnose what's going on.

Grind
Dose
Technique
Dwell Time
Temperature of water going north
Temperature of water when it starts heading south

All things we'd need.

-bry
Derryl,

Now I can see this is not your question... but it should be.

I think the real question is not, "Why does the dark roast stall in the vac-pot?" but rather, "Why are you using dark roasted coffee in the vac-pot?"

NO DARK ROAST on the vac-pot!

In all seriousness. Vac-pot/siphon brewing is about highlighting the dynamic flavors present in the coffee, about presenting the terroir, the varietal essence of THAT coffee. Dark roasting defeats that purpose.

To go a little further - I believe each brewing method has an optimum profile and range of roast for it. Now great coffee in X will still be great coffee in Y, but if you roast to present the elements accentuated by press, or you roast to illuminate those elements highlighted by the vac-pot, then it's a whole different ball game.

There is no benefit to using the siphon if you are dark roasting. Dark roasted coffee on the siphon just makes it a fancy looking brewer. Correct coffee at the correct roast on the correct equipment. If it didn't matter, then everyone would be great at it.


.... and to your question... I think the dark roasted coffee contains too many oils which cause the grounds to adhere in a cement like fashion to the abrasive area on the corey rod.... but I could be wrong.


Derryl Reid said:
Bryan
Grind, dose, temp, dwell time, techniques, temp is all consistent & it never fails with a medium or light roast! But a dark roast will stall more often than not.
Is it oily grinds or lighter grinds? I just can't figure it out!




Bryan Wray said:
Without being there and seeing all of the different aspects of what yhou are doing it's going to be very difficult for anyone to diagnose what's going on.

Grind Dose Technique
Dwell Time
Temperature of water going north
Temperature of water when it starts heading south

All things we'd need.

-bry
Hahaha!!
I do not disagree with you John P.
I do however like to see how my coffee tastes with different brew methods, my dark roasts are not usually overly roasted.
I just wanted to understand why? The brew usually stalls early in the siphon process and I was thinking the oils should still be floating.
Maybe a dark roast produces a little more "silt" or a "finer silt" ?
You could say that darker roasts are sort of more fragile.

When you grind coffee, there's structural energy in the coffee bean and in the grounds, and the grinder is applying force in a few different ways to break the coffee into smaller pieces. The darker the roast, the more fragile the coffee's cellular structure, and the more it will shatter as you grind. Lighter roasts have higher moisture, higher density, and a stronger structure. Lighter roasted coffee doesn't want to shatter as readily as darker roasts.

Yeah, so sometimes people over-simplify coffee grinding in their minds. They look at the burrs and think that it's all about those sharper edges cutting the coffee into smaller bits. It's not really so simple. There's cutting, rubbing, mashing, crushing, pulverizing, rolling, etc. The high-friction aspects of grinding will yield more fine-particles in the end with a darker roast than a corresponding lighter roast with all other things being equal.

"Maybe a dark roast produces a little more "silt" or a "finer silt."? Simply put, you're right!
Dark roast coffees also tend to be less dense, and have the ability to absorb and retain more water. One could theorize that a higher dust percentage, coupled with the dust's ability to absorb (and perhaps "puff up" more) than lighter roast could create a dam effect, blocking the water on the way down.

This is pretty speculative of course, something to think about. I support you in your effort to understand the performance of the coffee under different roast levels.

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