Speaker: William Lee
Host: Doireann O’Kiely & Kevin Moroney
Title: Nonuniform flow in coffee extraction
Abstract:
Coffee is a drink made by dissolving the soluble parts of ground, roast coffee beans in water. In espresso coffee this is done at high temperatures and pressures. It seems obvious that grinding coffee more finely will lead to more coffee being extracted. However, a recent experiment showed that, beyond a cutoff point grinding coffee more finely results in lower extraction. One possible explanation for this is that fine grinding promotes uneven extraction in the coffee bed. To explore this a low dimensional model in which there are two possible pathways for flow and coffee extraction is derived and analysed. This model shows that, below a critical grind size, there is decreasing extraction with decreasing grind size as is seen experimentally. In the model this is due to a complicated interplay between an initial imbalance in the porosities and permeabilities of the two pathways which is increased by flow and extraction, leading to the complete extraction of all soluble coffee from one pathway.