Grinding For Drip in Advance

[Mike White]

I've heard rumors suggesting that grinding for drip 12 hours in advance actually improves the quality of the cup. Something along the lines of stabilizing the gasses that are released to achieve more of an equilibrium during the brew process. We plan to cup several samples of the same bean/roast ground at different times (say, immediately prior, 1 hour prior, 3 hours prior, etc) to test this for ourselves, but I was wondering if anyone else already has? I believe Nick mentioned this in a podcast once, as did Scott Rao in his new book.

Any thoughts?

[Mark Prince]

The only argument I've ever heard for pre-grinding that actually made any sense to me, and seemed to show limited positive results for, was for press pot grinding.

The argument (from Bodum themselves) was that, because of the particle sizes, it didn't have the same CO2 leech off effect that grinding for drip or espresso did (espresso having so much more surface areas of the coffee exposed, vis a vis press grind at the same volume of coffee used) and because of this, you could pregrind as much as an hour or two before usage without much "loss" of quality extraction in the press. I got this suggestion after attending the restaurants and coffee seminar at the 2006 SCAA show.

When I got home, I ran a series of experiments - timed grindings of the same coffee to a press pot grind (area of 1000-1200 micron sizes) over six hours, one sample ground per hour with another sample ground 30 minutes before my scheduled brewing time, and a sample ground just before brewing. I ran this test twice over a week with two coffees.

The winning grind was the 'just before brew grind" but I did also notice there wasn't much degredation in the cup quality on the 30 minute grind. The 1 and 2 hour grind were virtually identical (I'm going from memory here, I don't have the notes I took handy at the moment), and the 3, 4, 5 and 6 hour grinds showed some increased degredation, with the 6 hour one very flat in all aspects - bloom creation, body, taste nuances, the works.

The power of CO2 in our ground coffee can never be underestimated in what it brings to the cup, imo.

I'd be interested to hear the results of your testing with drip grind.

Mark

[Mike White]

Interesting, thanks Mark. What about 12 hours? I've heard that specific number mentioned more than once.

[nick]

As far as I know, CO2 doesn't "bring" anything positive to the cup.

If anything, the opposite. The degassing of the coffee when water is introduced actually repels the water, reducing the contact, therefore the extraction. Some degree of carbonic acid can also be created.

When coffee is "too fresh," it's actually not "too fresh." It's got too much CO2... but the coffee itself is never more perfect to brew (in theory).

Grinding in advance is an attempt at further degassing the coffee (by grinding, which exposes more surface area) a bit more before brewing.

In my humble opinion, the holy grail of coffee is finding a way to get the CO2 out of the coffee as soon as possible after roasting, while still preserving the "freshness" of everything else.

[Mike White]

So Nick, with that in mind, it seems like there must be a point where the balance between freshness and "degassation" is optimal for brew. Since every roast and origin would degass and stale differently, am I on a wild goose chase? Even if we found the "prime time" during our cupping this week, it would certainly change with each coffee and roast.

[nick]

That's the problem.

When the coffee has just been roasted, the CO2 levels are at their highest, and it's also "freshest" (as far as positive fresh qualities).

As time goes on, CO2 levels reduce, which is a good thing... but it's also less fresh.

With an industry where 90%+ of roasters measure freshness in months, not days, this "super-specialty" level freshness needs some serious research and experimentation.

For instance, what's the best way to store the coffee when you can use it within 3-10 days of roasting? Valve? Non-valved? Under a vacuum (negative pressure) environment? FROZEN? Refrigerated? Is there some kind of substance that readily absorbs CO2 that could be put into a valve bag of coffee (removed before grinding, of course)... sorta like the little moisture-absorbing silica gel packs that come in certain products?

I've heard theories that if you froze coffee right after roasting, that CO2 could still leech out of the coffee (because of the size of the molecules), whereas the volatile flavor molecules would stay in the coffee. I've been meaning to test this... but then again... I'm 250 miles from our roaster.

[Mark Prince]

As far as I know, CO2 doesn't "bring" anything positive to the cup.

Read the illy books again, Nick.

CO2 in of itself doesn't provide flavours to the cup, but it is one of the primary flavour transporters for other elements to the bean. It is the reason why coffee blooms, and crema exists.

illy argues (and I've yet to see anything proved otherwise) that CO2 transports oils and lipids to the cup that otherwise would never leave the bean. CO2 also transports these flavours and aromatics during the resting stage, and the grinding stage (CO2 release, carrying with it other chemical compounds that "bond" to the CO2 gasses, is what you're smelling when you grind coffee).

Mark

[Mike White]

As time goes on, CO2 levels reduce, which is a good thing... but it's also less fresh.

Surely CO2 levels don't diminish at the same rate as freshness. Even if you experiment with freezers at the roaster, is there a way for us to definitively analyze the CO2 levels contained within?

http://www.foodqualitynews.com/news/ng. ... ts-improve

Tomas is modifying our infrared gas analyzer right now.

[Mike White]

[nick]

Read the illy books again, Nick.

CO2 in of itself doesn't provide flavours to the cup, but it is one of the primary flavour transporters for other elements to the bean. It is the reason why coffee blooms, and crema exists.

illy argues (and I've yet to see anything proved otherwise) that CO2 transports oils and lipids to the cup that otherwise would never leave the bean. CO2 also transports these flavours and aromatics during the resting stage, and the grinding stage (CO2 release, carrying with it other chemical compounds that "bond" to the CO2 gasses, is what you're smelling when you grind coffee).

Yeah. That all makes sense.

For espresso.

CO2 doesn't transport jack in brewed coffee... nothing that you want, or can keep around long enough to appreciate anyway.

[Mike White]

When I got home, I ran a series of experiments - timed grindings of the same coffee to a press pot grind (area of 1000-1200 micron sizes) over six hours, one sample ground per hour with another sample ground 30 minutes before my scheduled brewing time, and a sample ground just before brewing. I ran this test twice over a week with two coffees.

Did you leave the samples out in the open or enclosed somehow, like in a mason jar?

[Robert Goble]

Grind on demand -- I'm currently not buying any theory that has coffee sitting exposed to O2 in a ground state for any period of time before brewing. O2 is nasty stuff.

[Mike White]

I'm skeptical, but I've never actually tried it any other way (ground in advance). I'm mostly interested in testing these theories that I've heard.

[Jason Haeger]

Grind on demand -- I'm currently not buying any theory that has coffee sitting exposed to O2 in a ground state for any period of time before brewing. O2 is nasty stuff.

No kidding. The stuff seems to be absolutely terrible for everything but breathing biological carbon based lifeforms. Even then, I sometimes wonder if it's not just a necessary element for evacuating excess carbon from cells.

Who knows.

[stormer]

Grind on demand -- I'm currently not buying any theory that has coffee
sitting exposed to O2 in a ground state for any period of time before
brewing.

What about allowing the coffee to degas while in an inert environment such as nitrogen?

CO2 doesn't transport jack in brewed coffee... nothing that you want, or can keep around long enough to appreciate anyway.

What have you done to test this?

Even if you experiment with freezers at the roaster, is there a way for us to definitively analyze the CO2 levels contained within?

If you just want to compare degassing rates between the freezer and room temp, that should be easy enough. Just attach a hose to the valve of your bag of freshly roasted coffee and run it to a well-sealed plastic bag, which will inflate with time. To measure the volume of the gas, have a large beaker full of water inverted on top of a pan also full of water. Remove the end of the hose from the valve and run it under the lip of the beaker. Allow the vaccuum created by the weight of the water to deflate the plastic bag and jot down the volume of displacement. Congratulations, you just build a barometer.

[James Hoffmann]

Can people please explain the concept/mechanism of CO2 transporting things?

[Mark Prince]

Did you leave the samples out in the open or enclosed somehow, like in a mason jar?

Though Bodum didn't specify storage when they told me about this, I assumed they had used their coffee storage containers. I used zip lock bags for the test, squeezing out most of the air (not that it mattered much).

Mark

[Mark Prince]

Can people please explain the concept/mechanism of CO2 transporting things?

As I understood it last time I talked to a local UBC food scientist, it's about binding. Items that are not water soluble can "stick" to carbon dioxide, and move along with the gas (in many cases, forming tiny bubbles, not just in crema and bloom, but in other foods). The laymans terminology I was given (because I didn't understand the scientific babble) was equating it with soap and oils - soap's the thing that gets oils to leave your skin where water alone won't do it. I was told soap's not the only thing that can make this happen to skin, but the most common item.

IIRC, not all non-soluble chemicals, oils, lipids, etc can bind or attach to CO2, but some that dont bind to H2O will bind to CO2. I was surprised to find out during this convo that carbon dioxide is considered a solvent for this very reason. Apparently, it's used quite a bit in the oil industry to help crude flow better or something.

Eventually, C02 dissipates (heat, time, etc), but leaves behind (in the cup) the non-soluble elements it carried with it into the cup.

Mark

[phaelon56]

As I understood it last time I talked to a local UBC food scientist, it's about binding. Items that are not water soluble can "stick" to carbon dioxide, and move along with the gas (in many cases, forming tiny bubbles, not just in crema and bloom, but in other foods). The laymans terminology I was given (because I didn't understand the scientific babble) was equating it with soap and oils - soap's the thing that gets oils to leave your skin where water alone won't do it. I was told soap's not the only thing that can make this happen to skin, but the most common item.

This means that CO2 is a surfactant?

Nick said:

In my humble opinion, the holy grail of coffee is finding a way to get the CO2 out of the coffee as soon as possible after roasting, while still preserving the "freshness" of everything else.

Doesn't using the pre-wetting option of a Fetco extractor (I'm sure some other brewers must do this as well) take care of this? It's a bit like what most of us do with Mellita or Chemex brewing - pour a bit of water in to saturate the grounds, allow it to bloom a bit to let the gases escape and then pour in remaining water to brew.

[barry]

If you just want to compare degassing rates between the freezer and room temp, that should be easy enough.

Mike Sivetz already did that years ago & published the results.... He even gave a few seminars on it at SCAA.

[Tim Dominick]

http://slk020.liberty3.net/SCAA/blobs/cfiles/2005/02/SCAACONF_2000_Sivetz.pdf

You might need SCAA user name and password to see this article. This is one from 2000 that Mike Sivetz presented. There is another audio from his "preserving freshness of just roasted beans" from 2004 that might contain some of the same information. Gotta love the SCAA library and Barry for remembering that this kind of research has been carried out.


Mike presents siginificant data to back his claims and nowhere does he indicate pre-ground coffee as an option for higher quality. Indicating that near complete oxidation has taken place within the first hour or two after grinding. He also states that lineoleic acid, a significant player and close to 1/2 of the acid composition, is a very fast reactant to oxygen and quickly removed from the coffee after grinding. According to his paper, CO2 is not absorbed into the ground coffee and released at far greater rates due to increased surface area.

Aromatic loss is seen as the greatest threat to pregrinding coffee. Loosing most or all of the linoleic acid would certainly alter the aromatic composition, for better or worse would be in the eye of the taster.

[Mark Prince]

CO2 doesn't transport jack in brewed coffee... nothing that you want, or can keep around long enough to appreciate anyway.

Nick, are you thinking about only the elements you can see? ie, surface bubbles, crema, bloom? A lot's going on in the crafting of coffee at the microscopic level. CO2 plays a huge role here, no matter the brewing method.

Mark

[aaronblanco]

Can people please explain the concept/mechanism of CO2 transporting things?

As I understood it last time I talked to a local UBC food scientist, it's about binding.

There is a decaffeination process that uses liquid carbonic (CO2), is there not? In that process, if I recall correctly, CO2 is used to stick to caffeine and pull it out of the bean. I think that is also the same or a similar process using Ethyl Acetate to decaffeinate. Can anyone more in the know about Swiss Water process talk about how that works in extracting caffeine? Is it similar?

I think discussing how caffeine is extracted via decaffeination is relevant because of the whole binding thing Mark mentioned.

[Andy Schecter]

http://slk020.liberty3.net/SCAA/blobs/cfiles/2005/02/SCAACONF_2000_Sivetz.pdf

He also states that lineoleic acid, a significant player and close to 1/2 of the acid composition, is a very fast reactant to oxygen and quickly removed from the coffee after grinding.

Thanks for the great link. Minor correction: lineoleic acid is 1/2 of the OIL....

[barry]

There is a decaffeination process that uses liquid carbonic (CO2), is there not? In that process, if I recall correctly, CO2 is used to stick to caffeine and pull it out of the bean. I think that is also the same or a similar process using Ethyl Acetate to decaffeinate.

No, it's not the same, except in the broad "solvent pulls caffeine out of coffee" sense.

Can anyone more in the know about Swiss Water process talk about how that works in extracting caffeine? Is it similar?

Yes, the solvent (water) pulls the caffeine out of the coffee.

I think discussing how caffeine is extracted via decaffeination is relevant because of the whole binding thing Mark mentioned.

A molecular solid going into solution will form a bond with the solvent. Degassing is a known transport mechanism for volatile aromatics within the bean. Sivetz extracted and isolated these compounds in his efforts to isolate the "fresh" coffee aroma. Reducing or halting the outgassing of CO2 also reduces or halts the loss of these aromatic compounds. Grinding releases all of it... IIRC, 75% of the CO2 is lost when the coffee is ground. A remaining portion is lost when the ground coffee sits. CO2 can impede extraction during brewing (although this is typically not a problem with espresso, due to the pressures used in brewing), and this can be tested with a TDS meter. My experience has been that coffee which has not degassed has to be ground finer than coffee which has degassed in order to achieve similar extraction levels.