Learning from the magic bean

Learning from the magic bean

Learning from the magic bean

How becoming a coffee snob taught me about scientific experiments

January 13, 2023 | Rachel S. (MechE)

Mechanical Engineering

It all started when COVID hit. I had all this newfound time while attending classes on Zoom and found an outlet – specialty coffee. Before I knew it, I had become a full-blown coffee aficionado who knew all about the full coffee production process and cared about flavors in coffee. I found that the best way to get the cleanest flavors out of whole bean coffee was to brew it using the pour-over method. At the time, brewing my own coffee was a way for me to find everyday happiness during the pandemic – every sip allowed me to savor the flavor and step away from whatever I was doing. Little did I realize that until the things I learned from brewing pour-over coffee translated well to scientific experimental methods I picked up in graduate school. 

Making pour-over coffee is quite like following a chemistry procedure (except you can drink what you make at the end). It took a lot of practice to make good pour-over coffee and to get better at my chemical procedures. From having a steady hand while pouring from a gooseneck kettle or while pipetting a solvent to streamlining a procedure by parallelizing tasks, I learned through repetition. I eventually reached a point where I memorized my coffee and chemical procedures, knowing exactly when and how to do each step efficiently. 

Like any experimental procedure, a pour-over recipe can be edited to better optimize the output. In this case, our goal is to extract optimal flavors from the coffee. In short, coffee will taste sour if underextracted or bitter if overextracted. Properly extracted coffee will taste complex, with sweet, ripe flavors and have a long finish (aftertaste in throat). Different beans will have different extraction “profiles”; I have fun figuring out how to optimize flavor by changing brew variables. Here’s a sample procedure for making pour-over. 

  1. Boil water to 205-210 degrees F (96-99 degrees C) 
  2. Measure out N grams (20g) coffee and grind to medium coarse setting (particles should have sea salt consistency)
  3. Place and wet the filter, then discard the yucky paper water from your mug! 
  4. Pour in the ground coffee to the wet filter in the dripper and tare the scale. 
  5. Start the timer. Pour in 2N grams (40g) water in small circles (swirl the brewer if not all grounds are saturated). 
  6. At 30-45 seconds, pour 7N grams (140g, total reading 180g) water into the center of your dripper, pouring at a rate of 0.2N grams/sec. Swirl the brewer.
  7. At 1 minute 15 seconds, pour another 7N (140g, total reading 320g) grams of water into the center of your dripper. The rate should be around 0.25N grams/sec in this step but can be more flexible. Do not overflow the dripper (too much water) and ensure that the coffee bed is not exposed (too little water). Swirl the brewer again. 
  8. Water should be done running through all the grounds at 3-3:30 mins. If your total brew time is shorter than this, consider grinding coffee finer next time and vice versa. 

As with any experiment, variables affect the outcome. Let me outline some variables and steps that can change in the above procedure to optimize extraction (see a more nuanced explanation here):

  • Grind size: This is arguably the most important and tunable variable in pour-over. Particle size corresponds to surface area: finer grind size means more surface area for extraction and vice versa. This is best adjusted after seeing how long it takes for your entire brew to finish (i.e., all water leaves the bed of grounds in the dripper). If your brew takes too long, then grind your coffee coarser for your next brew. Because of this, a coffee grinder is a great investment! I have used burr grinders (not blade grinders) from Baratza, OXO, and Bodum and all of them have yielded fantastic cups of coffee. (For more information on coffee equipment, James Hoffmann’s YouTube channel is popular among coffee aficionados). 
  • Water and coffee quantity: Also known as the water-to-coffee ratio, different people have different preferences on this. For pour over, common values are 15:1 to 18:1 water to coffee. Less water means more condensed flavor, while more water means more watered-down flavors. 
  • Water temperature: Water temperature should be kept just below boiling to avoid burning and overextracting coffee. However, if water temperature is too low, you’ll need to brew or extract for a longer period of time (like the concept of cold brew). 
  • Number of pours and water flow rate: This can vary drastically depending on the dripper you own and your personal flavor preference. This is where the most experimentation happens – you have the freedom to make your own recipe! (In fact, there are competitions for this.) 

Keeping track of these variables taught me how to properly change variables and effectively log data from experiment to experiment. Like keeping a lab notebook, I would write on sheets of paper taped to the wall above my kettle to keep track of my brew variables, noting grind size, water and coffee quantities, and water temperature. By both brewing coffee and synthesizing chemicals, I quickly learned that changing several variables at once made it hard to keep track of how each variable affected the outcome. Changing one at a time between experiments and brews allowed me to directly see how much a given variable affected the output. 

Coffee introduced me to the enigma of data analysis. In the first couple brews when optimizing brew variables, it was hard to tell what flavors to look for other than the hints on the bag. It took dozens of different types of beans to help me develop my palate and know what “good coffee flavors” taste like. As a now-second year graduate student, I am still learning how to distinguish good and bad data and how to interpret and communicate my results. 

Ultimately, growth takes time – as does completing a PhD! But through coffee brewing and scientific experiments, I have learned that each step of the process allows for lots of valuable growth and skill building.

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