Intra-particle coffee brewing?
A few filter-brewing thoughts to throw out there for comment.
Pre-wet during filter brewing is an important concept to understand. When the brewing water first hits the coffee grounds, especially when the coffee is very fresh, a great deal of carbon-dioxide and other trace gases are dissipated. If brewing with a large-batch filter drip brewer, this can over-flow the brew-basket, and you surely don’t want that! Even with single-cup filter brewing, the fact is, if CO2 is actively coming out of the grounds, the water will have a hard time getting in. Think of it as a temporary and weak force-field around the coffee. It will slightly repel the water, leading to a weak brew.
Instead, hit the grounds with a portion of water (water with about 2-2.5 times the mass of the coffee) and wait for the bloom to subside before pouring more water. Now the coffee is better-prepared for brewing. This is more relevant to brew-through or pour-over methods, because in full-immersion brewing methods the solution remains in the same space as the slurry for the duration of the brew that make this less necessary. However, the corresponding caveat would be to make sure that you don’t have a floating, gassy cake of coffee during the brew. Those upper grounds aren’t really interacting in the brew. Slight agitation after 30-60 seconds should take care of that.
Now most of you reading this knew about that already, but I thought I’d throw that in for the beginners. Okay. Moving on… (more after the jump)
Recently, there have been a few murmurs out there of a newer technique for brewing pour-overs: the long pre-wet.
Usually, a pre-wet bloom period is 10-30 seconds. Longer? 60 seconds? 90 seconds?
It’s been reported that this longer pre-wet yields a higher overall extraction than the more typical 10-30 second pre-wet. With many of the shorter (less than 3 minute) brew-time methods often resulting in under-extracted cups, these longer pre-wet methods seem to help extend the brew-time and lead to fuller-tasting coffee1.
Question is, why does this work? A few theories are already starting to develop out there. Here’s mine, and a related variation on it.
The reason you pre-wet, to recap, is because you’re otherwise essentially wasting some of the brewing-potential of the first 20-30 seconds of the brew. Instead of picking up the solubles, a good bit of the water will just flow through and down and into the cup. So pre-wetting and waiting for most of the gas to dissipate helps the brewing to be more effective.
Fact is, when the grounds are wet, the brew begins, whether you’ve got a tiny bit of water or a lot of it. (Hot) water + coffee grounds = coffee brewing. What is coffee brewing? Solids dissolved by the solvent. Even a tiny bit of water will brew the coffee, provided you’re not at or too close to the saturation point2.
So even during the pre-wet, whether long or short, you’re still brewing the coffee. It’s just that the brewing is only happening within the coffee grounds, with nowhere for the solution to go, since it’s being retained in the grounds3.
So theoretically at least, the long pre-wet could help extend brew times. The immediately apparent down-side is that the brew temperature will likely be too low to extract properly. Using this theory, perhaps the answer is to simply add water in pulses over a longer period of time, not being afraid to let the brew slurry to appear to dry-out. We know it’s not really dry.
Try dialing-in this technique yourself and report your findings!
1 This was reportedly developed by the Intelligentsia “educator team,” led by Stephen Morrissey and Kyle Glanville.
2 If you had a shit-ton of coffee and only a little water, you could theoretically reach the saturation point of the solution, meaning the point at which the coffee solution is so strong that it won’t act as a solvent anymore. I’d be interested to see some experiments out there to find out what the solvency rate it as the brew strength goes up.
3 Coffee grounds generally retain water in the amount of double the mass of the grounds (i.e., 20g of coffee will retail 40g of water)
too busy to reply fully to this but here is a quickie on part of my weakly-unified theory…
“bloom” or preinfusion: coffee absorbs water, off gasses CO2.
“new water” enters the solution: differential between *new water* and *heavier solution embedded inside expanded particles* = osmosis = extraction of heavier brewed coffee.
thus the temp of the “new water” (for lack of better term) has much less impact as the heavy lifting of coffee solubility has already been taken care of and simple osmosis across a solute differential finishes the job.
I have much more to say on this but it’s unlikely to happen this week.
@tonx: I dunno man.
Your theory assumes that osmotic pressure would be noticeably higher with “new water” vs. a <1% aqueous solution. I don't think it would be.
I also believe the premise behind the idea of "heavy lifting" is questionable.
The good AND bad news is, as with many such discussions, only tasting together along with the discussion can really resolve anything. There should be a barista camp!
The 2:1 retention of water is what you get at the END of the cycle. During the intense off-gas period, it seems like the amount of actual brewing being done by the “tiny bit” of water is greatly reduced, if not stopped altogether by at least two factors:
1) The release of the C02 from the ground probably results in the rapid cooling in the micro-region where the gas is evacuated (think of a can of compressed air going frosty as you lower the pressure). PV=nRT and all means colder water, which is less of a solvent.
2) Some of that water that initiated the off-gassing will be immediately expelled (turned into bubble structures), so it is no longer inside the cellular structure of the individual coffee ground particle.
I’m guessing that very little brewing takes place until the hydrostatic pressure of the water overcomes/equalizes the gas pressure inside the grounds and the saturation can begin in earnest.
There’s a whole lotta pocket science going on here, Nick.
Our findings are 100% empirical, and we used several different data points, including brew strength, extraction percentage, temperature (slurry, kettle exit and coffee exit) and most importantly taste.
hey, that’s a nice photo. who’s sexy hands are those?
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In my opinion(as a newbie student), if we put a bit colder water at about 80 or less degrees to avoid the brewing of coffe, just to let CO2 dissapear and aferwards put a bit warmer water about arround 96 to execute the brew would be a solution.
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