What's the best Roast Development Time (DTR) and Finish Temperature?

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I’ve been asked this question in class and seen it online innumerable times.

"What has the greatest impact on a finished roast, the roast development percentage or the finished drop temperature of the beans? After reading lots of Scott Rao, his favorite coffees are usually between 20 and 25% development, but these roasts seem to lose all character. Help me understand how to balance these factors!"

Preface: This is not your fault.

Fictions like this are common and popular. The illusion of clarity they provide is really the promise of eliminating your burden of choice.

This is a big deal because all of coffee (and most of life) is a process of sequential choices.

Philosophically, one of the biggest choices humans make is to choose the middle ground between the twin discomforts of allowing others to make your choices or to do the work necessary to become better at making choices yourself.

A healthy sense of self-esteem makes micro and macro decisions about everything enormously easier.

If you've not thought of it yet or in exactly this way before:

    • Self-esteem is the reward of accomplishment.
    • Self-esteem means doing enough work long enough to trust yourself.

That doesn't mean you're automatically going rogue. "Self-made" people are necessarily built by amateurs. I'm only advocating that you'll develop more skill more quickly by listening to people that tell you "why" more than "how."

To put too fine a point on this:

    • Arrogance is self-esteem absent the work.
    • Love is what we are supposed to feel for those who encourage the work, support our accomplishments and foster the development of authentic self-esteem.

Why development ratio recommendations fail:

Coffee professionals know that "ideal" development time prescriptions are useless because people call first crack and prefer their coffee in wildly different ways. 


Real development truths:

    • No matter how you roast or what you roast on, the outside of the seed heats first. The outer seed color is always a function of finish temp.
    • Heat penetrates and roasts the inside of the seed over time and the development time dictates the inner seed roast color.
    • Shorter post first crack development times always measure and cup lighter and longer times always cup darker.
    • When comparison cupping, you'll notice a 2F difference in finish temp and/or a 15 second difference in development time about 95% of the time.
    • Your finish temp is about 70% of what your customers taste.
    • Your post first crack development period is probably 20-25% of what your customers taste.

Why? Because chemistry is most reactive at heat. The rate of development in your coffee starts slow and doubles about every 18F or 10C.

If the rate of development was money and you started out at 70F with a single dollar, by 400F you'd have $262,144. By 2nd crack at 420F you'd have doubled again to $525,288.

Your finish temp is the point of greatest velocity of chemical change in the coffee. Successfully hitting your roast flavor target means discharging the coffee into the cooling tray at the exact instant your inner and outer seed development best contributes to your choice of flavor in the cup.

It's not catching a speeding bullet. It’s catching an accelerating bullet.

Magic happens when you've got the machine control and the sensory skills to identify and differentiate the intensity of flavors in the cup.

Failure happens when you biff it and that magic goes up the exhaust stack. But don't sweat biffing a roast. It's coffee, not heart surgery. Biffing it is not an existential crisis. If it is, you're either in need of therapy or an even lower stakes career path. Maybe consider running for Congress.

The truth is your customers love you and your coffee for what it does as much as how it tastes. You're doing four batches per hour. Love them back by trying again and trying until you can reliably serve them magic on demand.

If you’re jazzed enough about coffee to have found and read this blog post, you're not an imposter. People are probably drinking your coffee and greatly enjoying it.

If this wasn't so, you'd be posting a resume not asking roasting questions.

Books can be useful, but they don't roast, drink or buy coffee. You choose your finish temp, post first crack development time, and what your coffee tastes like.

And enjoy the journey.

If you still remain completely befuddled, call me at the office and we'll talk it through.

- Steve

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  • Thanks for this. I often try to explain the roast for any given bean as a function of learning and control (then subsequent learning and better control). I dislike the attempt of so many others to prescribe a set standard of rules or to demand such a standard. The finish temp as you said it’s as close to a role “rule” as we can get but even then it’s somewhat relative to first crack and overall time in some degree.

    Christian Jolly on
  • Love it! Now do one on what % of the ROR curve we can taste….a topic that has also misled many roasters.

    For development, I now tend to view end temp as a softer target depending on how long roast time is and batch size. If I am hitting within 2degF with similar times and gas settings then I won’t see a difference in weight loss or ground color. I would rather hit my development time and be close to end temp vs the other way around. Personal preference. Maybe I should write a book.

    Alex on
  • The biggest message I should’ve read when I first started. No time like the present, thanks Steve. Well said.

    Meg on

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