"One more cup of coffee 'fore I go..." (click 2 check Bob's song)
Coffee a magical potion. Coffee is a potent drink for writing the thesis or writing papers or to start interesting hydrological discussions. Not only the fuel of work but also a ritual and moment of peace.
Fika with friends and colleagues.
Bitter taste to pleasant
My first contact with coffee-ish beverages was at a summer job on a tulip farm. A dispenser supplied instant coffee with milk powder. Luke water made the powerder drinkable. Too much sugar made the bitter taste disappear and become drinkable and, more importantly, supplied extra energy to chop off lily and tulip heads.
The instant coffee did not stick. The first foamy cappuccino on holiday instead did. Young and unfamiliar with C8H10N4O2, five cups were too much to stop jumping around. A lesson learned: The coffee intake remained relatively low afterwards. On cycling holidays, filter coffee replaced the instant cappuccino slowly, and to save weight, sugar was rationed.
The bitter coffee taste, slowly changed to something tasty - especially well-brewed bitter-sweet espresso.
Exploreing coffee berries
It took until my internship/thesis in the Makanya catchment in Tanazia that I encountered real coffee. After weeks of instant coffee, the common type of brewing, high up in the mountains of the catchment grew green and orange red berries on a bush. Coffee! We were inviated with the village head who invited us for coffee. Instead of instant coffee this time real coffee rosted on a fire, coursly grinded and brewn with coffee. I expected a strong cup of joe and dreamt of real espresso. Instead it was a weak brew, kind of diluted brown water. Althought the taste was not the one I expected the guesture wonderful.
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| Coffee berries on the bush |
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| Fresh coffee berries in Tana |
The filter coffee turned to Moka and a morning ritual.During my post-doc travel to Costa Rica, I encountered a different way of brewing coffee: in a sock. Coffee is ground coarsely and in a cotton/ linen sock shape filter where hot water is poured in. Depending on the person who brews, it can become a nice strong brew or "agua chacha" (tasteless brown water). Costa Rica is a beautiful country and produces world-class coffee with unique terroirs creating different tastes.
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| Wonderful espresso in Costa Rica |
Coffee hydrology
During the pandemic, I explored the world of special coffees from home. Reading and watching up on coffee e.g.
How to brew - coffee and water ratio
RecipesI suddenly realized while teaching online that coffee is next to a drink, which is also a great analogy to explain hydrological processes.
In the end, brewing coffee is nothing more than Darcy's law Q=-K x A x I
Discharge (Q) depends on the material property (K), the filter area (A) and the gradient over the filter (I). The material property K depends on the grind size of the filter and the preferential flow path through macropores or evenly distributed grains. The gradient depends on the amount of water poured on the filter or pressure applied in a fully automated coffee machine. The flow rate and grain size distribution affect the extraction efficiency, i.e., how much caffeine the water can extract from the grind. In the end, it is similar to hydrochemistry, how rainfall interacts with soil and geology, and how long water resides in the subsurface. There are many different YouTube channels (e.g. J. Hoffmann) to learn about coffee, and when observing, also learn about geohydrology subconsciously.
Next to popular YouTubes and wesites there is acctual a field of coffee sciences with papers in journals on coffee check, e.g.
- Coffee extraction: A review of parameters and their influence on the physicochemical characteristics and flavour of coffee brews
- A new methodology to estimate the steady-state permeability of roast and ground coffee in packed beds
- Water quality for Espresso coffee
- Suppressing the coffee stain effect: how to control colloidal self-assembly in evaporating drops using electrowetting
- Experimental and modelling: Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment
- Method comparison: Comparison of espresso coffee brewing techniques
and even on how coffee grounds affect soil properties
Check also a short video on evaporation and condensation
Coffee hydrology and teaching
Coffee is great to break the ice in online and in class teaching. A nice coffee hydrology question developed, to my knowledge by Prof. emmeritus Allan Rodhe (in case I am wrong let me know) and I use in teaching at Uppsala Uni - BSc course 1TV015 Meteorologi, hydrologi och miljömätmetoder: "Here comes some coffee brewing hydrology" combines Darcy and the massbalance:The figure below shows a coffee maker. For simplicity, it has a cylindrical filter holder with a horizontal filter at the bottom. All coffee outflow takes place through the filter. During brewing, the water supply from the water heater is 0.11 L min-1, which after a while gives a stationary water level with the figure b = 8.0 cm. When the water heater inflow stops, place your empty cup under the brewer. The cup is cylindrical with the same inner diameter as the filter holder. Filter holder diameter = 6.0 cm and height of the ground coffee a = 5.0 cm. How long does it take to fill the coffee cup with 6.0 cm of coffee?
When the inflow to the brewer ceases, the water level drops, the total potential gradient over the coffee powder decreases and the water flow decreases. Calculate the water level as a function of time and hence the time for a certain lowering of the water level (= the increase of the cup's coffee level).
For solution pass by the next class of 1TV015 😊
After all the writing, I need first a fika with ....
