I roasted a couple sample batches today from a small estate in the Carmo de Minas region of Brazil. The beans were a gift for a friend, but I rarely pass up the opportunity to probe for changes based on single variables. If you don’t want to “geek out” on coffee science, you might as well quit reading now, and enjoy a latte, because this is going to be a heady and opinionated entry in the notebook.
The first roast was light, dropping the beans about 2 minutes after the start of first crack. For the second roast, a little more heat was applied during development and the beans were held in the roaster an additional 40 seconds, producing a darker roast, but not what I would call “Full City”. I suppose these would be referred to as a City and City+ roast, respectively, but these terms are very subjective, as is just about everything having to do with coffee.
Both roasts were ground and brewed exactly the same, 17 grams of coffee to 38 grams water. My first test was comparing extraction, as measured by Total Dissolved Solids. The lighter roast measured 8.4% TDS and the darker roast measured 7.65% TDS. Since I am using a refractometer that measures sucrose, and because sucrose is burned off in the roasting process, I suspect that the difference I am reading is due to the reduction of sucrose in the coffee, and not a difference of more or less extraction. This points to a problem faced by anyone who is trying to collect data throughout the coffee process. There really is no definitive method of measurement that works in the field. Refractometers don’t really measure coffee, they measure a component found in coffee, and thermocouples don’t really measure internal bean temperature, they measure environmental temperature as it is impacted by the surface temperature of a bean mass. We can extrapolate conclusions based on the data, but with the current state of the art, we are getting a fuzzy picture at best.
My second comparison was taste. Again, this is incredibly subjective. I don’t claim to be a coffee “cupper” so I won’t attempt to describe flavors using cupping terms. I did not notice any difference in strength of flavor, again indicating that the difference in TDS is very subjective. From experience, I know that a 1% difference in TDS on the same roast is very noticeable. Also, the coffees tasted virtually the same with the lighter roast appearing to be slightly more sour, until the temperature dropped to around 125°F. At this point, a range of fruity sweetness was noticeable, sweeter in the light roast, a little less so in the darker roast. Neither roast suggested bitterness at any temperature.
I have enjoyed this batch of Carmo de Minas beans under various roasting conditions and they have never disappointed, both as a light roast, and well into 2nd crack. I don’t think most people would notice the difference between today’s roasts, unless they tasted them side-by-side, but when it comes to extracting the best potential flavor out of a roast, 15° and 40 seconds does make a difference. This is why I experiment, and why I keep a notebook.