Time to get your nerd on like Donkey Kong. Or something like that.
I’ve keeping up to date on the most excellent Bitter Press blog as Jesse has been fleshing out his new format. Pretty interesting for those who don’t know; he’s decided to only have one post at a time but with a post that is very weighty and informative. It makes the whole operation feel relevant and fleeting.
The latest post has my inner nerd both applauding and desiring a little clarification. I love how he’s embracing the scientific understanding of coffee extraction. But there are both variables that I think he overlooks and terms that I feel need to be redefined.
First, he does not take the level of roast into account in his extraction equation. While I cannot link to any sources on this, a darker roast will extract quicker. This is because the grounds are less dense than a lighter roast which allows for quicker saturation. Again, this may be BS, but my own empirical experience backs this theory up.
Second, pressure speeds extraction in ways that I don’t fully understand. I know that at the nine bars of pressure in espresso extraction the insoluble oils are emulsified into the beverage, but even at less pressure the extraction profile changes. An Aeropress is different than a pour-over and I really believe that the added pressure is a factor.
Third, he does not take account how long off the roast the coffee is. Granted this is not terribly important past a day or two, but it is very important for the home roaster.
Last, the importance of agitation is the movement of water over the surface of the coffee. Of course, if you agitate a brew after it has steeped a while it will mix the less saturated water in with the more, but that is less important than the movement of the water. Of course, his point still stands that agitation is a great extraction enhancer and should be used with caution.
If nothing else, I really hope everyone who reads this immediately reads everything they can from Jesse. Good writing is a pleasure to read and good writing about coffee is my favorite.