Jim Schulman came to visit with me for a few days last week and when we were not busy gorging on some of the finest dishes New York has to offer, we managed to do a few informal experiments with pre-ground coffee. What prompted that line of investigation was Scott Rao's excellent book The Professional Barista's Handbook
. In his book, Scott details the following experiment: He grounded freshly roasted coffee and let it sit for 12 hours in room temperature. He then brewed it and compared it to coffee brewed from freshly ground coffee. The 12 hours pre-ground coffee was better tasting and sweeter than the fresh ground batch. Scott speculated, that the result is also applicable to espresso brewing.
My only experience with pre-ground coffee was during the two days Jim and I spent with George Howell and Peter Lynagh at Terroir
. There, a coffee that was pre-ground 2 weeks (!) ago was brewed and compared to a freshly ground brewed coffee. The purpose of that experiment was to compare properly stored green coffee (vac packed at origin) with badly stored green coffee (jute bag). The properly stored coffee pre-ground 2 weeks before brew beat the badly stored green freshly ground by a mile. However, that two week old batch was no match for a freshly ground sample of the same coffee.First Experiment: Brewed Coffee
So, with that in mind, we designed two experiments: In the first one we essentially repeating Scott's experiment. We pre-ground a batch of 2 day old Geisha Esmeralda (Jim's roast) and waited 12 hours. We then brewed it in the Eva Solo (soak Pot) for four minutes at 198 f 8 oz water and 13.6 grams ground coffee. At the same time, we freshly ground the same coffee and brewed it side by side in another pot.
I invited my friend Lisa to join us in the blind tasting. In this experiment, Jim & I played the role of the somewhat refined coffee connoisseur, while Lisa played the role of the average Lisa.
The result was unanimous: The pre-ground coffee was sweeter, and as a whole better integrated. It still had all the high notes that I thought may get lost somewhat in 12 hours, and it was somewhat rounder.Second Experiment: Espresso
In this experiment we used two different coffees. The first was a typical espresso blend we picked up from a coffee shop in the city. Barrington Espresso Blend, from Joe The Art of Coffee. That coffee was not more than 5 days from roast. The second was a single origin Jim roasted Worka - a relationship coffee from Sidamo sourced by Ric Rhinehardt and it was three days from roast. We pre-ground a shot 30 minutes before brewing it and compared it to a freshly ground shot of the same coffee. We chose 30 minutes due to the Italian conventional wisdom about storage of ground coffee in the doser. (The Italians pre-grind coffee to fill-up the doser and then dispense it per shot.)
Here we got split results:
The Barrington blend (15.5 grams 1.7 oz 198f 27 seconds): The 30 minutes pre-ground came on top. The shot was better integrated, rounder and a bit sweeter. There was no loss in flavor profile.
The single origin shot (14.5 grams 198f 1.5oz 26 seconds) was the reverse. The freshly ground came on top, it was richer and more complex; one of those shots I would give a 5 in a barista competition.
There was one area where the pre-ground shot was ugly on both experiments: The extraction, as viewed on a bottomless p/f. The pre-ground was uneven to the extreme, and yet, despite it, it tasted better with the Barrington blend.
Those results require more experimenting, with larger samples to get a clearer view of what's going on there. Scott believes that pre-grinding creates a more even distribution of CO2 in the coffee bed and thus more even extraction which results in a more balanced and sweeter cup.
The brewed coffee experiment has been repeated by others, and I hear they all came to the same result: pre-ground was better. The espresso on the other hand is very intriguing, and I think it is coffee dependent. This is only an uneducated guess. Time from grinding plays a bigger role in espresso, and I doubt a 12 hours pre-ground espresso will be a match for a freshly ground batch.
A tentative conclusion here would be that sharper coffees (overly acidic for example) will benefit from pre-grinding for espresso.
It is also important to note, that there was no difference in crema or the way the shot looked in the cup between the ground and pre-ground.