I was about 18 when I first made coffee from roasted coffee beans. I boiled the coffee twice and was very
confused when it didn’t all dissolve. Well, I then found out, IT DOESN’T!!!
Coffee brewing in the turbo mode? A happy combination of comfort, flavor and inspiration.
Scientist have identified about 1000 different chemical compounds in roasted coffee. It is a mighty little gem packed with flavors. No wonder we are so obsessed with it. But the coffee beans is only up to about 25~30 % dissolvable, meaning, it will never be completely brewed off, with the exception of maybe burning it to ashes. We keep talking about bringing the maximum flavor out of the coffee, does that mean we should brew as much out of the beans as physically possible?
The tricky part about brewing good coffee is that not of all these dissolvable compounds are pleasant to human palate. Caffeine, for example, is extremely bitter to taste. So by achieving a good brew, we are actually looking to bring a balanced result of extraction, not too little, not too much, so the finished brew has an adequate presence of sweetness, body and acidity, a happy combination of comfort, flavor and inspiration.
The commonly preferred extraction rate is between 18% to 22%.
Unfortunately it’s not possible to cherry pick what chemical you want to extract from the coffee when you brew it (yet). But since chemical has different properties, there are ways to use physics to influence the process.
Coffee science saves the day
I know a lot of people who share the same passion for coffee. But when we talk about making coffee, it’s pure science.
Take water temperature as a case study. Water solubility is temperature dependent and generally increases with temperature*. The hotter the water, the easier it can dissolve matter. Now throwing in coffee brewing to the equation. Higher temperature will favor the extraction of less polar compounds, some of which we usually identify more with being bitter and astringent. Hot water is good, because it brews efficiently; hot water is also not good, because it may brew too much of the stuff we don’t want. What a dilemma!!
The perfect solution we find in this case is temperature control. We heat water up to a certain temperature that is hot enough but not too hot. With a thermometer, this solution is highly repeatable.
For the actual execution, we also need to take into consideration the ambient temperature, the heat retainability of your brew gear and even how your brewing method effects heat loss, and eventually come to a parameter that accounts for all the potential temperature drop in the process. For example, the general recommended range is between 195~201°F (measured at coffee slurry) . I would heat the water up to 205°F when I’m in a somewhat less heat-loss scenario, or I would even use off boiling water if there are more temperature reducing factors.
More is not always better
It’s always about finding the sweet spot, isn’t it? What about roast level? What about grind size? Are all coffee grinder the same? These may seem like trivial questions, but they do make an impact on cup quality one way or the other.
Coffee extraction factors:
roasted coffee quality
water quality and brew temperature
brew ratio
grind quality (particle distribution in relation to brew environment.)
brew method (decoction/immersion/percolation/pressurized)
sampling method (serving temperature, with milk or other ingredient?)
In conclusion, I would like to simply say that, yes, coffee is rocket science. Also a disclaimer: squeezing coffee beans is NOT a brewing method, do not attempt this at home.
* Frédéric Mestdagh, Arne Glabasnia, Peter Giuliano "The Brew-Extracting for Excellence"