Coffee Roasting Analysis| What is Under-development and Over-development? How to Determine Roast Degree?

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Coffee roasting is a professional craft. Many data-driven enthusiasts study the curves of champion roasters and try to replicate them, little realizing that even if the roasting curves are very similar, what about the flavor? I have met many roasting masters who rely on extensive experience and intuition to roast coffee beans, not just on data and curves.

"Perfect curve? so what!?"

Indeed, our ultimate goal in roasting coffee is to produce a delicious cup of coffee, not just impressive data. The curve serves as a reference, showing how this coffee bean behaves during the roasting process. Ultimately, we must judge quality through flavor and mouthfeel evaluation—just as a coffee that achieves "Golden Cup Extraction" might be "correct" but not necessarily "delicious."

Understanding "Underdeveloped" and "Overdeveloped" Roasting

Returning to our topic, let's discuss what we mean by "underdeveloped" and "overdeveloped" roasting. These two conditions cannot be easily determined from roasting curves alone.

First, let's examine underdeveloped coffee

Underdeveloped coffee beans are typically roasted too lightly and carry flavors of grass, vegetables, and toasted bread—essentially, the beans are dropped before good flavors have emerged during roasting. This situation usually occurs when there's a sudden temperature drop after first crack, or when roasting at low temperatures for an extended period after first crack. Visually, underdeveloped coffee beans will have black creases along their center line that haven't fully expanded. After drinking, you'll experience a numbing, tingling sensation on the tip and sides of your tongue (insufficient degradation of chlorogenic acid).

Solution:

Visual observation—for washed coffee beans, the center line should be fully expanded, and the silver skin should be relatively clean, with uniform color—this is an excellent judgment method. Use your nose—underdeveloped coffee beans will emit grassy aromas during roasting rather than fragrant smells. Finally, avoid dramatic drops in RoR (rate of rise) after first crack or deliberately extending the roasting time too long.

The image above shows underdeveloped coffee beans on the left and well-developed beans on the right.

Now, let's discuss overdeveloped roasting

Overdevelopment has two meanings: one is roasting too dark, where flavors are burned away, leaving only bitterness. This is common in many "charcoal-roasted" coffees and often appears in beans roasted until they become oily. But can coffee be overdeveloped even when not roasted dark? Absolutely.

The image above shows overdeveloped coffee beans. Don't they look underdeveloped? The bean surface appears dry, but their center line has completely opened—this is one manifestation of overdevelopment.

Coffee beans that are overdeveloped despite not being roasted dark occur due to excessive development time during the late stages of first crack, resulting in flavor loss. The main taste characteristics are burnt grain flavors, flat taste notes, and roasted aromas. The brewed coffee color will also be relatively pale, with an oily mouthfeel (distinguished from full body).

Solution:

Mainly, after first crack, observe when the beans have expanded, sample them to identify aromas, and when the expected fragrance is achieved, decisively drop the beans (this requires experienced judgment) rather than maintaining roasting within a temperature range. Additionally, for beans from certain regions, such as Panama Boquete coffee beans, you especially cannot develop for too long after first crack, and you don't need to wait for complete expansion—otherwise, the bean core will become darker than the surface, meaning overdevelopment has occurred, and flavors will be diminished, resulting in flat-tasting coffee.

For beans like Geisha, having some creases is actually normal!

Final Thoughts

Roasting coffee beans requires considering many aspects of the raw beans: variety, growing environment, processing method, moisture content, water activity, and more to formulate a roasting approach. Then, through multiple adjustments and cupping sessions, find a roast that brings out better flavors (which includes the roaster's subjective preferences). If you're competing, a beautiful roasting curve might seem "fairly accurate" or "not too bad" to judges, but to achieve delicious coffee, it ultimately comes down to cupping and brewing. Among the factors that determine coffee flavor, the quality of raw beans is particularly important (as are storage conditions). As roasters and baristas, our ultimate goal is to express the best qualities of a coffee bean rather than deliberately trying to change it (failed attempts are even more embarrassing).

Important Notice :

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