Presentation Information
[O09-P01]Dripping coffee to understand soil liquefaction process★Invited Papers
*Kei Kurita1 (1.Earthquake Research Institute, The University of Tokyo)
Keywords:
drip coffee,soil liquefaction process,packing fraction
This is a second report on dripping coffee in relation to soil liquefaction process. In 2025 JPGU we presented "liquefaction and dripping coffee" ( O08-P04 in Kitchen Earth Science session ). When we drip coffee hot water is poured incrementally by 30g. In this procedure density and color are measured for each dripped coffee. After dripping stops at each pouring some amount of water remains in the interstitial space of coffee grains. By tapping the dripper this water is expelled out above. Vibration induced by tapping destroys grain packing structure and resultant local consolidation pushes water out. The surface water finally permeates inside and forms the last drip. This process is analogus to soil liquefaction induced by earthquake shaking. Every morning we are happy to have fascinating time to watch how soil liquefaction is going on.
In this second report we focus on the problem how the amount of remained water is controlled by what factors. The amount of remained water is closely related with the interstitial volume of coffee grains, the packing fraction. In the uniform grain size system the maximum packing fraction( interstitial volume) is 33.3%. But in an actual case such as our daily coffee making much lower packing fraction is set such such as the close loose packing. Furthermore if there exists distribution of grain size the packing fraction varies so much. Also if the grain shape deviates from spherical one it also changes. In our experimental set-up( in the sense of kitchen earth science ) we have no reliable methods to determine packing fraction of coffee grain in the dripper. In stead we can determine the amount of remained water after each pouring procedure. In the upper graph of inserted figures the water content in coffee grain in the dripper is shown as a function of pouring step. During initial several steps water content increases. This suggests rearrangement of grain packing occurs by water pouring process. This is also indicated by variation of extracted volume of coffee with time. The actual permeability increases steadily with pouring cycles.
We use two types of coffee powder; one is commercially available one with specifying grain size. For example Shop Kaldi provides coffee powder with grain size degree 1(fine) to 9(coarse). Another one is by using milling machine. Longer milling time yields more uniform and finer grains. In the lower two graphs show how the milling time controls the amount of remained water. The lower right diagram shows time variation of mass of dripped coffee at late stage pouring. The samples with longer duration of milling have more gentle slope. The lowe left diagram shows variation of remained water with milling time.
The amount of expelled water after tapping should be controlled by the amount of interstitial volume and fragility of packing structure. Non-uniform grain-sized sample could have lower interstitial volume because smaller grains can fill the vacant space formed by larger grains while it ha weaker strength. In the coffee system the amount of expelled water ( thus the amount of liquefaction fluid ) is determined by competing these two processes.
In this second report we focus on the problem how the amount of remained water is controlled by what factors. The amount of remained water is closely related with the interstitial volume of coffee grains, the packing fraction. In the uniform grain size system the maximum packing fraction( interstitial volume) is 33.3%. But in an actual case such as our daily coffee making much lower packing fraction is set such such as the close loose packing. Furthermore if there exists distribution of grain size the packing fraction varies so much. Also if the grain shape deviates from spherical one it also changes. In our experimental set-up( in the sense of kitchen earth science ) we have no reliable methods to determine packing fraction of coffee grain in the dripper. In stead we can determine the amount of remained water after each pouring procedure. In the upper graph of inserted figures the water content in coffee grain in the dripper is shown as a function of pouring step. During initial several steps water content increases. This suggests rearrangement of grain packing occurs by water pouring process. This is also indicated by variation of extracted volume of coffee with time. The actual permeability increases steadily with pouring cycles.
We use two types of coffee powder; one is commercially available one with specifying grain size. For example Shop Kaldi provides coffee powder with grain size degree 1(fine) to 9(coarse). Another one is by using milling machine. Longer milling time yields more uniform and finer grains. In the lower two graphs show how the milling time controls the amount of remained water. The lower right diagram shows time variation of mass of dripped coffee at late stage pouring. The samples with longer duration of milling have more gentle slope. The lowe left diagram shows variation of remained water with milling time.
The amount of expelled water after tapping should be controlled by the amount of interstitial volume and fragility of packing structure. Non-uniform grain-sized sample could have lower interstitial volume because smaller grains can fill the vacant space formed by larger grains while it ha weaker strength. In the coffee system the amount of expelled water ( thus the amount of liquefaction fluid ) is determined by competing these two processes.