Roasting
Development Time And What It Governs
The stretch of a roast that follows first crack is where flavour is finished, and its length relative to the whole roast is one of the most discussed numbers in the trade.
Roasters talk constantly about development, usually as a proportion of total roast time. The concept describes a real phase with distinct chemistry, though the number attached to it carries less meaning than its popularity suggests.
The phase begins at a physical event
Development time is measured from the onset of first crack to the moment the coffee is dropped from the roaster, so it is bounded by an audible event at one end and a decision at the other.
Before that point the bean is drying and building the precursors that later reactions will use, and its flavour is largely undeveloped.
After it, the structure has opened, heat penetrates more readily, and the reactions that generate roasted aromatics run considerably faster than before.
Under-development has a recognisable taste
A coffee dropped too soon after the crack tends to be sharply acidic, thin in body and to carry grassy or cereal notes underneath the acidity.
The interior of the bean has not caught up with the exterior, so the roast is uneven through its depth even though the surface colour looks acceptable.
This is a common fault in roasts chasing brightness, and it is often mistaken for the natural character of a high-grown coffee.
Over-development flattens the cup
Extending the phase too long continues the reactions past the point where they generate interesting compounds and into the production of generically roasted flavour.
Acidity falls away, origin character becomes hard to identify, and the coffee begins to taste of the roast rather than of where it came from.
Taken far enough this converges on the flavour of any dark-roasted coffee regardless of origin, which is precisely why dark roasts are traditionally used for consistency.
The ratio is a summary, not a control
Expressing development as a percentage of total roast time is convenient, but the same percentage can be reached by very different combinations of time and temperature.
A long slow development and a short fierce one can produce identical figures with entirely different results in the cup.
The rate at which bean temperature is rising through the phase matters at least as much, which is why roasters watch the shape of the curve rather than a single number.
Different coffees need different amounts
Dense beans from high elevations conduct heat inward slowly and generally need more time after the crack to develop evenly through their depth.
Softer, more porous beans reach the same internal state faster and can be pushed into over-development while the roaster is still waiting for a target figure.
Sample roasting and tasting remain the only way to find the right value for a given lot, which is why published targets are starting points rather than specifications.
