Evenness in Roasting - A Consideration

I've seen many posts around the internet with a picture of a sample roast and captions like "rate my roast", "does this look good?", "I can't get this coffee from (x) to roast evenly, what am I doing wrong?", "Is this tipping or scorching?", etc.

I've been reading and re-reading Rob Hoos' lastest book "Cultivar: A Practical Guide for Roasters" and it contains a treasure trove of phenomenal information on, of course, coffee cultivars, but also terroir, post-harvest processing and more. During my deep dive I started thinking about the rate at which different coffees roast; two different coffees roasted to the same specs won't necessarily roast to the same final color.

This then got me thinking about the aforementioned "evenness" posts and my own experience roasting the components for my espresso blend, both of which tend to drop out of the roaster with a range of colors. It's something I had originally accepted was beyond my skill to fix, but I'm start to wonder if it really is something that needs fixing.

To be clear, I'm not talking about roasting so that each individual bean is an even color across its surface. Especially in gas roasters, tipping and scorching are vital defects to identify, and often are indicated by an uneven color on any one bean's surface. What I'm talking about is evenness indicated by identical color between any two beans roasted in the same batch.

My core espresso blend component, a Peaberry offering from Tanzania, consists of Blue Mountain, Luwiro, Bourbon, and Kilimanjaro varietals. According to Rob, Typica (of which Blue Mountain is a descendant) and Bourbon beget fairly different roast profiles; they enjoy similar development times but want different total roast times. For Typica, Rob recommends 9 minute roasts, and for Bourbon 10:30+ roasts, both of which he says are for his "lightest" roasts.

So when roasting an offering that consists of multiple varietals from different families how could anyone expect that offering to roast to an even color across the whole batch? Every varietal will have slightly different densities and chemical make ups, meaning they take on heat and develop at different rates. So when a batch of different varietals is roasted to the same final temperature in the same amount of time, how could they roast to the same level?

I'm sure higher end and more experienced roasters than I have already come to this conclusion, but for anyone out there who has been chasing the white whale of a perfectly even batch of coffee, this is my current working theory:

Outside of single varietal offerings, roasting for even batch color is a wild goose chase that is likely to encourage a roaster to make choices that, in terms of flavor and aromatics, result in a lower quality product. Evenness is one variable of many to consider while roasting, and while it can be an indicator of potential defects it is not an indicator of roast quality.

Flavor is the number one quality indicator, and perfection is the enemy of progress. So don't get too caught up in how a coffee looks beyond defect prevention, and pulling out those quakers and burnt beans. Just taste, adjust, repeat, and have fun.

With love,

Noah