Uneven extraction in coffee brewing, research article

Want to talk espresso but not sure which forum? If so, this is the right one.
User avatar
Moka 1 Cup

#1: Post by Moka 1 Cup »

For anyone who might be interested:
Uneven extraction in coffee brewing

A recent experiment showed that, contrary to theoretical predictions, beyond a cutoff point, grinding coffee more finely results in lower extraction. One potential explanation for this is that fine grinding promotes non-uniform extraction in the coffee bed. We investigate the possibility that this could occur due the interaction between dissolution and flow promoting uneven extraction. A low dimensional model in which there are two possible pathways for flow is derived and analyzed. This model shows that, below a critical grind size, there is a decreasing extraction with decreasing grind size as is seen experimentally. This is due to a complicated interplay between an initial imbalance in the porosities and permeabilities of the two pathways in the model, which is increased by flow and extraction, leading to the complete extraction of all soluble coffee from one pathway.
Source: https://pubs.aip.org/aip/pof/article/35 ... ee-brewing
Life, Liberty and The Pursuit of Happiness.

Supporter ♡

#2: Post by dougmg »

Moderator note: Merged thread

https://sprudge.com/finer-grinds-lead-t ... 07243.html
"Our model shows that flow and extraction widened the initial disparity in flow between the two regions due to a positive feedback loop, in which more flow leads to more extraction, which in turn reduces resistance and leads to more flow," said co-author William Lee. "This effect appears to always be active, and it isn't until one of the regions has all of its soluble coffee extracted that we see the experimentally observed decrease in extraction with decreasing grind size."


#3: Post by BodieZoffa »

Thing is science will never trump taste, instinct, etc. Of course some will try to nitpick every variable to the last possible detail looking for a (possible) more decisive answer, but that time/effort wasted should be spent on just extracting more espresso and consume as much as humanly possible!

Nathan King

#4: Post by Nathan King »

There have been several studies about this, and it makes sense if you think about it. Grinding finer increases surface area and therefore extraction...until channeling begins. Channeling lowers the extraction because some amount of grounds are effectively bypassed and left un/under extracted.