17:15 〜 19:15
[O08-P04] おいしいコーヒーの入れ方と地盤液状化現象
★招待講演
キーワード：ドリップコーヒー、浸透流、粒子配列の破壊、地盤液状化
The processes in dripping coffee have many similarities in earth science. It is basically permeable flow of hot water with extractions of chemicals from coffee grains. The taste and flavor of coffee are controlled by the varieties of processes, which invoke large amount of experimental, theoretical and simulational researches. From earth science curiosity these researches are quite important to invoke our curiosity towards earth science process. This report is a simple essay what I am observing and thinking during dripping coffee.
Every morning I am making coffee by drip. During waiting time for dripping I watch the surface of water-covered coffee grains. When I add hot water incrementally for example by 30ml high flow rate from a dripper is observed at the first stag in each cycle, then flow rate gradually decreases and finally the flow ceases. Associated with this the surface is covered with water at first then all the water infiltrates into grains and the surface appears to be dry. In the first several cycles the surface is partially covered with bubbles then bubble-free area appears near the center and gradually expands and after about 5 cycles all the surface becomes bubble-free and granular. This seems to be a timing to stop dripping. In this succession color of the extracted coffee changes steadily from deep black to translucent and flavor and taste become weaker and fainter. The images show temporal change of the surface state. Expansion of bubble-free area can be seen from left to right with cycle advancement.
Next step is not merely observation but a bit quantitative measurement by using digital balance to determine temporal variation of flow rate. We can roughly estimate effective permeability at each cycle. In the first several cycles up to 3 permeability decreases while after that it says almost constant. This indicates arrangement of grains packing occurs toward better packing state. Combining with the previous simulation work( Mo et al 2021 )we can interpret flow-induced arrangement of grains occurs at the first several stages and later on packing state stays constant and stable stream paths seems to be established. The timing of vanishment of the surface bubbles corresponds to this transition.
When we vibrate the dripper after water drains out by tapping several times intrigue phenomena occurs. Water exudes to the dry surface at first and then infiltrates, flows out from dripper. This is caused by rearrangement of grains induced by tapping which destroys stable structure, expels interstitial water. This phenomena is same as liquefaction of soils by earthquake shaking. The amount of expelled water changes with particle size and its distribution. Ground coffee by coffee mil at home is generally characterized by wide grain size distribution where as commercially available This reflects amount of interstitial water ( pendular water ) and this is controlled by surface tension.
Please enjoy this simple experiment in relaxing morning time of holiday and think about seismic liquefaction.
Moroney, Kevin M., Ken O’Connell, Paul Meikle-Janney, Stephen B. G. O’Brien, Gavin M. Walker, and William T. Lee. 2019. “Analysing Extraction Uniformity from Porous Coffee Beds Using Mathematical Modelling and Computational Fluid Dynamics Approaches.” PloS One 14 (7): e0219906.
Lee, W. T., A. Smith, and A. Arshad. 2023. “Uneven Extraction in Coffee Brewing.” Physics of Fluids 35 (5). https://doi.org/10.1063/5.0138998.
Mo, Chaojie, R. Johnston, L. Navarini, and M. Ellero. 2021. “Modeling the Effect of Flow-Induced Mechanical Erosion during Coffee Filtration.” The Physics of Fluids, September. https://doi.org/10.1063/5.0059707.
Every morning I am making coffee by drip. During waiting time for dripping I watch the surface of water-covered coffee grains. When I add hot water incrementally for example by 30ml high flow rate from a dripper is observed at the first stag in each cycle, then flow rate gradually decreases and finally the flow ceases. Associated with this the surface is covered with water at first then all the water infiltrates into grains and the surface appears to be dry. In the first several cycles the surface is partially covered with bubbles then bubble-free area appears near the center and gradually expands and after about 5 cycles all the surface becomes bubble-free and granular. This seems to be a timing to stop dripping. In this succession color of the extracted coffee changes steadily from deep black to translucent and flavor and taste become weaker and fainter. The images show temporal change of the surface state. Expansion of bubble-free area can be seen from left to right with cycle advancement.
Next step is not merely observation but a bit quantitative measurement by using digital balance to determine temporal variation of flow rate. We can roughly estimate effective permeability at each cycle. In the first several cycles up to 3 permeability decreases while after that it says almost constant. This indicates arrangement of grains packing occurs toward better packing state. Combining with the previous simulation work( Mo et al 2021 )we can interpret flow-induced arrangement of grains occurs at the first several stages and later on packing state stays constant and stable stream paths seems to be established. The timing of vanishment of the surface bubbles corresponds to this transition.
When we vibrate the dripper after water drains out by tapping several times intrigue phenomena occurs. Water exudes to the dry surface at first and then infiltrates, flows out from dripper. This is caused by rearrangement of grains induced by tapping which destroys stable structure, expels interstitial water. This phenomena is same as liquefaction of soils by earthquake shaking. The amount of expelled water changes with particle size and its distribution. Ground coffee by coffee mil at home is generally characterized by wide grain size distribution where as commercially available This reflects amount of interstitial water ( pendular water ) and this is controlled by surface tension.
Please enjoy this simple experiment in relaxing morning time of holiday and think about seismic liquefaction.
Moroney, Kevin M., Ken O’Connell, Paul Meikle-Janney, Stephen B. G. O’Brien, Gavin M. Walker, and William T. Lee. 2019. “Analysing Extraction Uniformity from Porous Coffee Beds Using Mathematical Modelling and Computational Fluid Dynamics Approaches.” PloS One 14 (7): e0219906.
Lee, W. T., A. Smith, and A. Arshad. 2023. “Uneven Extraction in Coffee Brewing.” Physics of Fluids 35 (5). https://doi.org/10.1063/5.0138998.
Mo, Chaojie, R. Johnston, L. Navarini, and M. Ellero. 2021. “Modeling the Effect of Flow-Induced Mechanical Erosion during Coffee Filtration.” The Physics of Fluids, September. https://doi.org/10.1063/5.0059707.