Guide to Judging Yellow Point and First Crack in Coffee Bean Roasting: What Causes Underdeveloped and Astringent Flavors in Coffee?

Introduction: The Reality Gap Between Theory and Practice

As the title suggests, this article by FrontStreet Coffee is primarily about mental preparation for friends who are about to embark on coffee roasting. In the first five lessons of "Coffee Roasting from Scratch," only very basic roasting theories were explained. The simplicity level is roughly equivalent to the "multiplication table" in mathematics.

We must recognize a reality: theory is often perfect, but practice often presents unexpected situations. For example, when you have thoroughly studied FrontStreet Coffee's roasting curve theory from the first five lessons and generally understand the concepts of bean drop point, yellowing point, first crack, heat, damper, and time.

The First Challenge: Operating the Roasting Machine

When you confidently proceed with your first practical session, you discover that "your brain gets it, but your hands don't." When you start operating, you find yourself asking "why isn't the temperature keeping up," "why is there so much smoke when the beans come out," "focusing on recording data while forgetting to adjust the heat, leading to confusion," resulting in complete loss of confidence after several batches.

This situation is completely normal. Getting familiar with operating the roasting machine, the relationship between heat and damper adjustments and temperature rise, requires a certain feel. Even experienced masters need to roast two or three batches on a new machine before getting the feel. Therefore, the first point of practice is to master operating the roasting machine, simply put, being able to achieve desired temperatures through heat adjustments. (Temperature rise has lag time; after adjusting heat, effects typically appear after 30 seconds, so you need to learn to anticipate.)

The Second Challenge: Identifying Key Roasting Points

After passing the "trial of roasting machine operation," please don't get too excited, because at this point you're just a "heartless boiler operator." Just like a new driver who just got their license hitting the road, you discover that the standardized and fixed practical skills learned in driving school don't help much on actual roads.

Although at this point you understand the basic theoretical knowledge of roasting and know the theories for judging yellowing point and first crack, when it comes to actual operation, you find yourself wondering "has it changed color yet," "has it already turned yellow," "was that a crack just now," "why hasn't the second sound come yet, does the first sound count," "or was I just hearing things."

You'll doubt your vision and hearing. As a beginner, when judging these key points, you should try to align with the standards used by others, otherwise communication with others can lead to "talking past each other." FrontStreet Coffee will use text to describe various situations where misjudgment might occur.

For judging the yellowing point, washed coffee is relatively easy to identify, as it changes from light green to yellow. However, sun-dried or anaerobic sun-dried coffee beans are harder to judge because their raw bean state is light yellow, and the color change during yellowing may not be obvious enough.

Additional Indicators for Yellowing Point

Below, FrontStreet Coffee adds two indicators to assist in judgment: the first is temperature, generally yellowing begins after 150°C; the second is aroma, before the yellowing point, coffee beans have grassy and wheat aromas, while after yellowing, these aromas disappear and are replaced with sweet corn aroma.

The Challenge of Identifying First Crack

The judgment of the first crack point affects the overall drop time. Our basis for dropping beans is based on the development time after first crack and the drop temperature. If "your judgment" of first crack time is later than the "actual" first crack time, then when everyone records the same development time, your roasted coffee will be darker than others. Conversely, if "your judgment" of first crack time is earlier than the "actual" first crack time, then when everyone records the same development time, your roasted coffee will be lighter than others, possibly resulting in underdeveloped flavors. (A 20-second difference in development time can cause very noticeable flavor changes.)

Why is the "first crack" point so difficult to judge? FrontStreet Coffee's criterion for the beginning of first crack is the continuous appearance of a second crackling sound. The sound of first crack is very crisp, like the "crackling" sound made when using an electric mosquito swatter.

FrontStreet Coffee believes the reason for easy misjudgment is that "false crack sounds" appear before the crisp "crackling" sounds. False crack sounds are not as crisp and sound somewhat muffled, mainly because some defective beans or individual beans that roasted faster crack first. These beans crack due to their own defects and incomplete heat absorption, so the remaining sound appears muffled. Individual coffee beans might, due to luck, often stay at the bottom during drum rotation, absorbing more heat than other coffee beans, thus cracking first and emitting crisp crackling sounds, but after one sound, the second doesn't come for a long time - these are "early starters" and cannot be counted as the first sound of first crack.

The Final Challenge: Taste vs. Expectations

The final thing that breaks beginners is "I followed the roasting curve exactly, and the bean color looked good when they came out, but when it came to tasting, they tasted terrible." This is indeed quite frustrating. After working hard to roast a batch of coffee beans that seemed quite good, enduring anxiety and waiting 8 hours for cupping, only to face a shocking disappointment.

If you're currently facing this situation, please don't be discouraged. "There are thousands of curves that can roast good coffee, and roasting curves are infinite. Is it possible that your roasting curve wasn't suitable from the beginning?" In the previous roasting classes, FrontStreet Coffee also expressed that when it comes to roasting curves shared online, everyone should not copy the data but understand the logic behind the data. Summarize the reasons from each failed roast, address these defects, and you can find a curve that suits you.

Important Notice :

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