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mkraft
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Posted Sun Feb 24, 2013, 11:18am
Subject: What causes coffee 'sludge'?
 

What causes the sludge that forms in a cup of coffee that's been left sitting?

Does it result from tiny coffee grains that weren't filtered out during the grinding/brewing process and have eventually dropped to the bottom of the cup and congealed . . .

-or-

. . . does some of the coffee, if left sitting in a cup, inevitably precipitate (in the 'chemical' sense -- i.e., become solid and separate from the liquid) and form the sludge?

Put another way, does 'sludge' form in a sitting cup of coffee even when efficient grinding/brewing methods have been used?

Thanks.

 
non si sa mai
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Netphilosopher
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Posted Sun Feb 24, 2013, 2:18pm
Subject: .
 

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calblacksmith
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calblacksmith
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Posted Wed Feb 27, 2013, 7:04am
Subject: Re: What causes coffee 'sludge'?
 

You do not mention the method of brewing. A French press will have MUCH more sludge in the cup, that is why I do not like the FP. Drip will be much cleaner. I prefer Vac Pot brewing for it's inclusion of coffee oils and the clean pot it produces.

 
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mkraft
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Posted Wed Feb 27, 2013, 2:31pm
Subject: Re: What causes coffee 'sludge'?
 

calblacksmith Said:

You do not mention the method of brewing. A French press will have MUCH more sludge in the cup, that is why I do not like the FP. Drip will be much cleaner. I prefer Vac Pot brewing for it's inclusion of coffee oils and the clean pot it produces.

Posted February 27, 2013 link

Yes, I thought about that after posting, but then decided I could rely on the info in my 'profile' in the sidebar:
Bialetti Caffetiera stovetop

It's interesting that you write about coffee-cup sludge from French press.  I don't use French press because I could never get a strong enough brew.  But because the recommended French press grind is relatively 'large' I would not expect grounds to get into the coffee -- i.e., they should be filtered out by the press mechanism, shouldn't they?

How can one really determine whether or not the 'sludge' (in a cup that's been sitting for a while) is the result of the precipitation mentioned in my original post (in which case it's not really 'undesirable'), rather than due to uneven grind that's resulted in smaller coffee grounds not being trapped by the stovetop espresso maker's filter?

Thanks.

 
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jpender
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jpender
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Posted Wed Feb 27, 2013, 2:53pm
Subject: Re: What causes coffee 'sludge'?
 

mkraft Said:

Yes, I thought about that after posting, but then decided I could rely on the info in my 'profile' in the sidebar:
Bialetti Caffetiera stovetop

It's interesting that you write about coffee-cup sludge from French press.  I don't use French press because I could never get a strong enough brew.  But because the recommended French press grind is relatively 'large' I would not expect grounds to get into the coffee -- i.e., they should be filtered out by the press mechanism, shouldn't they?

How can one really determine whether or not the 'sludge' (in a cup that's been sitting for a while) is the result of the precipitation mentioned in my original post (in which case it's not really 'undesirable'), rather than due to uneven grind that's resulted in smaller coffee grounds not being trapped by the stovetop espresso maker's filter?

Thanks.

Posted February 27, 2013 link

Unless you use a sieve on your coffee there will always be smaller particles. It's just the nature of grinding coffee that they are produced. The amount depends on the grinder and the grind.

I use a stovetop and find there is a fair amount of both fines that settle quickly and suspended solids that take longer to settle (or never do). I've tried to filter these out and measure them and I estimated something between 8-10% of the solids in the cup could be filtered with standard filter paper. To really get at what you are asking you'd probably want to use a finer filter, perhaps a sub-micron syringe filter. You could filter a small amount of coffee hot into a test tube and let it cool. Wait. See if you get anything at the bottom.
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mkraft
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Posted Thu Feb 28, 2013, 11:52pm
Subject: Re: What causes coffee 'sludge'?
 

jpender Said:

Unless you use a sieve on your coffee there will always be smaller particles. It's just the nature of grinding coffee that they are produced. The amount depends on the grinder and the grind.

Posted February 27, 2013 link

I have a feeling that there people here who would take issue with that and who believe that a top-quality grinder should produce a 100% consistent grind.

I use a stovetop and find there is a fair amount of both fines that settle quickly and suspended solids that take longer to settle (or never do). I've tried to filter these out and measure them and I estimated something between 8-10% of the solids in the cup could be filtered with standard filter paper. To really get at what you are asking you'd probably want to use a finer filter, perhaps a sub-micron syringe filter. You could filter a small amount of coffee hot into a test tube and let it cool. Wait. See if you get anything at the bottom.


Coffee cup sludge isn't something I find so undesirable as to make me want to go high-tech (sub-micron syringe filter, testtube, etc.) to try to escape from it. I  would expect a good quality 'paper filter' to be able to remove all the grinds that found their way into the brewed coffee -- if they are in fact what causes the sludge.  Aren't those filters intended to do just that when used with 'drip' coffeemakers?

I've used paper filters a few times (i.e., after brewing in a stovetop maker) but would prefer to find a method of brewing that minimizes or removes the grinds that form the 'cup sludge' that doesn't require multiple stages.  (I wonder what all those Italians with their stovetop espresso-makers do.  Maybe their attitude is:  "A little a-sludge-a?  A-who a-cares-a?")  ;)

Thanks for your reply.

 
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jpender
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Posted Fri Mar 1, 2013, 11:17am
Subject: Re: What causes coffee 'sludge'?
 

mkraft Said:

I have a feeling that there people here who would take issue with that and who believe that a top-quality grinder should produce a 100% consistent grind.

Posted February 28, 2013 link

Consistent, but not all the same particle size. There are always fines.

Take a look at the grind profile for the Baratza Preciso, a $300 grinder: http://www.baratza.com/wp-content/uploads/PRECISO-Graph.pdf

mkraft Said:

Coffee cup sludge isn't something I find so undesirable as to make me want to go high-tech (sub-micron syringe filter, testtube, etc.) to try to escape from it. I  would expect a good quality 'paper filter' to be able to remove all the grinds that found their way into the brewed coffee -- if they are in fact what causes the sludge.  Aren't those filters intended to do just that when used with 'drip' coffeemakers?

Posted February 28, 2013 link

I was just suggesting a way to try and answer your question, "Does (the sludge) result from tiny coffee grains... -or- ... precipate (in the 'chemical' sense". Even paper filtered coffee has tiny particles in it, whether they settle on the bottom of your cup or not.

mkraft Said:

I've used paper filters a few times (i.e., after brewing in a stovetop maker) but would prefer to find a method of brewing that minimizes or removes the grinds that form the 'cup sludge' that doesn't require multiple stages.  (I wonder what all those Italians with their stovetop espresso-makers do.  Maybe their attitude is:  "A little a-sludge-a?  A-who a-cares-a?")  ;)

Posted February 28, 2013 link

I can't speak for millions of Italians but some amount of sludge is unavoidable with a coarse metal filter. You can make it better or worse with the grind. If you want it cleaner, one approach I've heard of is to put a piece of filter paper into the pot itself.
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DavecUK
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Posted Fri Mar 1, 2013, 12:17pm
Subject: Re: What causes coffee 'sludge'?
 

Also with french press a LOT of the problem can come from poor technique in using the french press, not just from an inadequate grinder.

With espresso (or americano), I get almost no fines in the cup when extracting by machine.
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calblacksmith
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calblacksmith
Joined: 25 Nov 2007
Posts: 7,468
Location: Riverside, Ca, U.S.A.
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Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Wed Mar 6, 2013, 3:24pm
Subject: Re: What causes coffee 'sludge'?
 

Even with great grinders, you will have some fines, they just happen, it can't be helped.

I have used FP on and off for years, now it has been ... off for at least 5 as I just like a cleaner cup, I have no issue with those that like FP, great! It just is not for me.

YMMV!

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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