Why Rest Beans at all?

[Ryder]

Here is a lively debate on the subject as it relates to espresso. Most people say resting is more important for espresso.

Wow, that's a great thread! I'm brewing siphon, so I think that I'm *especially* immune to a lot of the considerations to espresso extraction.... the carbonic acid issues especially...

In any event, it is all an amazing experience to be trying all of these techniques.

One thing I will try is to grind about 10 minutes before brewing.... see what that does... most of the CO2 lost, minor oxidation...

The sad thing is, I'm just recovering from a cold... so I'm scarcely able to make any subtle taste comparisons

Ryder

[Ryder]

Gosh, Ryder, next you'll be telling us that little microparticles of aspirin don't have individual GPS navigation to guide them directly to the site of the pain.

They have the bloodstream for that. The aspirin superhighway

Ryder

[Weyesa]

I'd read the second link. One of the entries was done by a chemist and he gives a nice, technical discussion of the effects of heat on co2 release and how it impacts extraction. If I understood what he said, his explanation is that hot water releases more co2 and the rush of gas prevents water from getting in effectively. By the time that stops, the extraction is mostly over. Apparently something happens in the first 35 seconds that the co2 impedes, not sure how.

Also, the discussion of the acid was interesting. More co2 makes more carbonic acid which changes the flaccid by itself and the chemistry of the rest of the extraction.

[bigbells]

Here is a lively debate on the subject as it relates to espresso.

Agggghhhhhh!.. and I'm only up to March 23 2006 so far in the long thread!

A while later: After reading all 7 pages, I was kind of comforted by the fact that it turned into an "everyone's view is legitimate" sort of conversation.

[RDS]

We're told that the beans release CO2, which is all fine and dandy... but CO2 shouldn't be an issue... it's colorless and odorless... is this just a myth?

I am sure *something* is happening to the "bean" overnight... but the release of CO2 should not be an issue of any kind. We have CO2 in our throats, mouths and sinuses constantly that we produce ourselves.

Sorry to be a skeptic here, and obviously taste is an individual preference, but I'd really like to understand the chemistry of the "rest" a bit better.

I'm brand new to this forum, and I joined just so I could say something on this subject. I may know very little about roasting coffee, but I am a biochemist and I know a thing or two about acid/base chemistry and organic chemistry.

I agree with bigbells who said the original poster is missing the point about CO2. CO2 bubbling up when water is first added is a sign of recent roasting, but it doesn't act as much of a barrier to hot water in extracting the flavor components from coffee. I also don't think it has anything directly to do with the presence or absence of flavor.

The real barrier to extracting flavor from the grounds is that coffee's flavor oils are poorly soluble in water. It takes heat and time to extract these oily compounds from the grounds. They don't really dissolve so much as get suspended in hot water. You can see those shimmering oils floating on top of the coffee in the cup. When coffee is fresh, the grounds clump up when you first add water because there are enough flavor oils in the grounds to keep out the water. Extraction works better if you break up the clumps so the grounds can get wet. That's probably also why we need hot water, at about 205°.

Even before I roasted coffee, I knew that while making Melitta drip coffee I had to wet the grounds with some hot water and wait a minute or so before adding the rest of the water to get more flavor. And this was with beans that were not nearly so fresh. They never produced the CO2 foam that I can see now when I first add water.

I'm not at all sure what's going on with the rest time after roasting. The Kenyan Nyeri AA Gatomboya I recently had (its already gone ) took 3 or 4 days for its full flavor to develop. Why is that? I did notice that during the first day or two after roasting, very little gas was filling the bag, but by the 3rd day after roasting the bags became noticeably inflated each day. I'm guessing that when the gas comes out of the beans its a sign that they are ready to brew, but I wonder if it has anything directly to do with the flavor.

Thanks for reading my first and somewhat long post here.

Richard

[Sweet Maria's]

Awesome post, Richard. There are a number of physical and chemical changes that happen during coffee roasting that there has just not been any really solid research done on (outside of larger, Nestle-sized corporations, but even then there is less research done in regards to quality as much as volume output and such). As far as the resting after roasting argument is concerned and specifically with Kenyas, I wonder if there's something to be said about the specific acids present (phosphoric being one) and the rest time? Other coffees that share some of the same tropical fruit qualities that are the result of these acids, for instance some Maragogypes, also require at least 2 days before beginning to show their true potential.

- chris schooley

[MikeW]

Thanks Richard! Your description of breaking coffee into clumps may imply a better preinfusion method for Aeropress. I notice when I pour in a little water to wet the grounds, it only gets the top third wet. The bottom grounds are still dry. Maybe it's better to put in a little coffee, then a little water, then a little more coffee, and so on, so that it all has time to activate.

I've always had trouble visualizing what's different when wetting with a small amount of hot water, though.

-Mike

[RDS]

I read more of the espresso thread where the chemist Bob Barazza made his comments.

http://www.home-barista.com/coffees/why ... 89-10.html

I agree with everything he says. There is one big difference. We're talking about brewing coffee and he's talking about making espresso. Espresso is made at very high pressure and coffee is made at normal atmospheric pressure. At high pressure, the CO2 readily dissolves in the hot water making carbonic acid, just like an unopened can of soda. But at normal pressure, the CO2 quickly bubbles off, just like what happens when you first open that soda can. So what he has to say about carbonic acid and low pH doesn't apply for normally brewed coffee.

One other point. Since the coffee grounds are porous, and they are saturated with the coffee flavor oils, the hot water has to 'wet' or penetrate into the matrix of pores to complete the extraction. This does take a few minutes. The fresher the coffee, and the finer the grind, the more the grounds can clump up and delay getting wet. So stir up those grounds while they are getting wet.

Is stirring in an Aeropress easily done?

[MikeW]

Yes it is, and stirring is part of the recommended Aeropress brewing procedure. It was so obvious I didn't think of it!

(The Aeropress scheme entails putting coffee and water together in a tube, stirring the mixture, and pressing it out through a paper filter. Total brew time is 45-60 seconds, and grind is somewhere between espresso and "fine" drip.)

In what I believe is an earlier version of the AP instructions, it says to dribble water slowly for the first few seconds. Then pour the rest of the water and stir, it says. The newest version of the instructions doesn't mention pouring slowly at first.

Orthodox Aeropress brews last less than 1 minute, but many people experiment with brew times and grind levels.

-Mike

[MikeW]

I'll sum up my thinking on this: it seems like in the Aeropress scheme preinfusion is superfluous, because in a process where the mixture is stirred immediately, all the coffee is getting wet at the same time anyway.

-Mike