This is the direction I've been headed with my own brewing. I think if you want the most consistent extraction, it's going to be found with full immersion and then filtering. This patent describes exactly that.
"The present invention, unlike prior art processes and systems, controls the key brewing parameters, namely, brewing time (water-coffee contact time), exposure of ground coffee surface to uniform extraction conditions (constant gentle liquid-solids mixing in a suspension), uniform extraction temperature, and mass ratio of water-to-coffee (liquid-to-solid) in the mixing step. It is well known in the field of chemical engineering that the method that provides the most uniform batch contacting of fine solids with a liquid is a stirred tank reactor. The present invention solves the problem of uniform exposure of coffee grounds with water by contacting the solids and liquid as a mixed slurry, i.e. a mixed suspension of solids in liquid, rather than in a fixed bed of solids as in all previous coffee brewing concepts."
I'm not a chemical engineer so I had to look up stirred tank reactor and it's basically a cylindrical vat with a rotating propeller in the middle. It seems like you'd have to be really careful not to overextract with a propellor. It must be running at low rpm.
Posted Sat Sep 18, 2010, 8:50am Subject: Re: Weekend reading - Brew first, filter later
In theory it makes some sense. With a bed of coffee grounds, the side of the ground that is up against the side of the filter doesn't get extracted as much. If you get the grounds suspended in the middle of the water, every side of the ground will be properly extracted. This also speeds extraction which is useful for retailers.
That's theory. In reality, if you stir a mixture of coffee grounds and water for a minute straight you get truck stop, overextracted coffee. So the trick is finding the right balance where you are making the extraction slightly more even without overextracting. My latest settings are agitate for 3 seconds, let sit for 9 seconds, and repeat 8 times for a total of 96 seconds. I think you want to agitate just enough to get the grounds off of the bottom and sides of the brewing chamber, but not moving so rapidly that you greatly speed extraction. Just as the grounds have slowed down to the point they are about to hit the bottom of the chamber, you agitate again. In my tests, coffee would fall out of suspension too much with only a minute of steeping. In the end I might end up closer to 2 minutes of agitation/steeping.
If these methods really do produce a more even extraction, then I think you could expect to taste just a little less bitterness with the key flavors a little more defined. We're talking about subtle differences. But from a commercial standpoint, if you could produce a cup of coffee in 2 minutes that tastes the same or better than a 4 minute cup, than that would be very interesting.
Posted Sat Sep 18, 2010, 8:55am Subject: Re: Weekend reading - Brew first, filter later
Have you guys ever tried an Aeropress? It is very much like what you are describing. Total immersion and stirring the slurry in a cylinder - and then filtering. It makes very good coffee and costs about $23
EricBNC Senior Member Joined: 22 Jun 2010 Posts: 1,500 Location: North Carolina Expertise: Just starting
Espresso: QM Silvano Grinder: K30, Preciso, KyM Vac Pot: Want One Drip: Bonavita BV-1800 Roaster: Me
Posted Sat Sep 18, 2010, 9:09am Subject: Re: Weekend reading - Brew first, filter later
rwgamer Said:
In theory it makes some sense. With a bed of coffee grounds, the side of the ground that is up against the side of the filter doesn't get extracted as much. If you get the grounds suspended in the middle of the water, every side of the ground will be properly extracted. This also speeds extraction which is useful for retailers.
That's theory. In reality, if you stir a mixture of coffee grounds and water for a minute straight you get truck stop, overextracted coffee. So the trick is finding the right balance where you are making the extraction slightly more even without overextracting. My latest settings are agitate for 3 seconds, let sit for 9 seconds, and repeat 8 times for a total of 96 seconds. I think you want to agitate just enough to get the grounds off of the bottom and sides of the brewing chamber, but not moving so rapidly that you greatly speed extraction. Just as the grounds have slowed down to the point they are about to hit the bottom of the chamber, you agitate again. In my tests, coffee would fall out of suspension too much with only a minute of steeping. In the end I might end up closer to 2 minutes of agitation/steeping.
If these methods really do produce a more even extraction, then I think you could expect to taste just a little less bitterness with the key flavors a little more defined. We're talking about subtle differences. But from a commercial standpoint, if you could produce a cup of coffee in 2 minutes that tastes the same or better than a 4 minute cup, than that would be very interesting.
Please do not think I am mocking your post (last post offered "memorial services" for old coffee beans - still trying to recover what little credibility I may have here) but I own a device called Mr Coffee Coco-motion ($3 at Goodwill's everywhere) that maintains heat (won't boil water but won't loose heat fast from water poured from a boiling kettle either) and provides agitation. I am going to try this experiment and report back.
I chew coffee beans with my teeth while gargling with 195 F water to enjoy coffee. What is this "coffee brewing" device you speak of?
Ok, this is much better than what I was envisioning. Some how I just envisioned grinds being swirled around for 4min!
rwgamer Said:
In theory it makes some sense. With a bed of coffee grounds, the side of the ground that is up against the side of the filter doesn't get extracted as much. If you get the grounds suspended in the middle of the water, every side of the ground will be properly extracted.
I understand what you're going for here, but I'm still wary. The amount of coffee NOT getting extracted because it's against the filter or against the wall of the press is such a small amount that I don't know if it's even noticeable. And I'm also not convinced it's not being extracted as much. The perimiter grounds should still be getting saturated.
My fear here is that any powder will become more noticeable and the inconsistency of the grind (even the best grinders have powder and inconsintency) will be amplified. Again, I may be way off here.
So, you tell us; how has the experimentation been affecting the cup? Has it? Better? worse?
Posted Sun Sep 19, 2010, 9:24am Subject: Re: Weekend reading - Brew first, filter later
I'd never heard of the Coco-Motion. I checked it out on Ebay and it would solve one of the problems I've been having. I like my coffee really hot but I lose too much heat in 96 seconds.
This morning I did my 96 second brew and it was drinkable--just too cool and a little weak. In the beginning I was getting too much sediment or powder like you say so I made the grind coarser, more toward drip coffee size. I still haven't produced coffee that I prefer to my standard Krups brewer with cone filter, but I've only been at it a few days. I also did a control brew this morning (same time, no agitation), and it was very weak, so I know that my agitation is increasing the rate of extraction.
"I understand what you're going for here, but I'm still wary. The amount of coffee NOT getting extracted because it's against the filter or against the wall of the press is such a small amount that I don't know if it's even noticeable. And I'm also not convinced it's not being extracted as much. The perimiter grounds should still be getting saturated."
It's different than I thought. I was expecting the weight of the water to push some of the grounds to the bottom of the brewing chamber, but most of them actually float to the top. Those floating grounds have about half of their surface area exposed to the air and half to water. So those grounds that float to the top will be half extracted unless agitated and swapped with grounds that are totally submerged.
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