Why Coffee Beans Have Wrinkles: Roast Levels, Processing Methods, and Bean Structure Explained

 I don’t know if you’ve ever really taken a close look at the coffee beans you brew every day. Some beans have lots of wrinkles on the surface, while others look surprisingly smooth. So what actually causes that difference? Today, let’s talk a little about it — just enough to give you some fun coffee trivia to chat about with your barista, haha.

These wrinkles are actually caused by a kind of “shell collapse” that happens when the internal structure of the coffee bean goes through dramatic physical changes. Green coffee beans contain moisture and dense plant cell structures. During roasting, as the temperature rises, the water inside turns into steam, pressure builds up, and the gases try to escape outward. At the same time, structural materials like cellulose and lignin begin to soften and become more brittle under high heat.

After roasting, when the beans cool down, the remaining moisture and the carbon dioxide produced during roasting continue to slowly release from the bean. The cell walls that were once expanded by gas pressure begin to collapse as moisture and gas escape. Since the outer surface of the bean is less flexible than the internal cells, it can’t fully shrink back into a perfectly smooth shape. That’s what creates those uneven wrinkles and folds.

But then why do some beans still look smooth?

A lot of it comes down to roast level, bean density, and processing method. If you think about the smooth-looking beans you’ve seen, chances are many of them were light roasts. Lightly roasted beans expand less internally, experience shorter pressure buildup, and lose less moisture overall (usually around 12–15% weight loss during roasting). Because the cellular structure remains relatively intact, the surface stays tighter and smoother, with very few wrinkles.

The beans with the most obvious wrinkles are usually medium-dark roasts. These beans expand significantly during roasting, the surface stretches outward, and then they lose a large amount of moisture (typically 15–18% weight loss) while releasing gas. Once cooled, the structure collapses inward, creating those classic walnut-shell-like wrinkles.

Interestingly though, extremely dark roasts can actually appear smoother again. I’m talking about beans roasted well past second crack — the kind that become visibly oily on the surface. At this stage, the bean structure has already been heavily damaged. The surface becomes brittle and porous under extreme heat, often developing a shiny oily coating. The original fine wrinkles get flattened or hidden beneath the oil, creating more of a cracked appearance instead of detailed wrinkles.

But this smoothness is really an illusion created by oils and surface brittleness — very different from the smoothness of a light roast.

Light-roasted beans have a dry, tight surface, almost like a fully stretched drum skin. Their cell structure remains mostly intact, with little to no oil leakage, giving them a matte and delicate smoothness. Deep dark roasts after second crack, on the other hand, develop shiny, reflective surfaces that almost look wax-coated. That oily layer fills in the tiny wrinkles and creates a glossy reflection that makes the beans appear smooth. But if you look closely, you can still spot tiny crack-like patterns — almost like a dried riverbed — rather than the continuous smooth surface seen in light roasts.

Bean density also plays a role. High-altitude hard beans, which are denser, tend to expand more evenly during roasting, so their wrinkles appear more organized and uniform. Lower-altitude softer beans are more likely to develop irregular wrinkles.

Processing methods affect appearance too. Washed coffees usually look cleaner, and their wrinkles appear much more obvious compared to natural-processed coffees.

That’s because washed coffees go through fermentation and water washing after the fruit skin is removed, fully cleaning away the mucilage layer before drying. The resulting green beans have very clean surfaces with only a thin layer of silverskin remaining. Most of that silverskin falls off during roasting, leaving the surface fully exposed. So when the bean collapses and wrinkles form, they appear sharp, direct, and highly visible. Sometimes washed beans almost look like they’ve suddenly “aged” after roasting, haha.

So if you’re trying to guess a coffee’s processing method by appearance, here’s a fun clue: if you see lots of silverskin and very visible wrinkles, there’s a good chance it’s a washed coffee.

Natural-processed coffees are different. In the natural process, the entire coffee cherry — including the skin, fruit, and mucilage — is dried together. During drying, sugars and sticky fruit compounds cling to the parchment layer surrounding the bean, forming a semi-transparent hardened “sugar coating.” During roasting, this layer caramelizes into a brown, crispy shell that still stays attached to the bean surface.

Even if the bean underneath collapses and wrinkles, this caramelized layer softens and masks those sharp edges. Instead of detailed grooves and wrinkles, you see a smoother, more even surface with a slightly textured appearance.

When we drink coffee every day — especially Ethiopian beans, which are often tiny to begin with — washed beans can honestly look pretty “ugly.” Many people assume smooth surfaces and even coloring mean better-looking, higher-quality beans, especially with naturals. But that’s also a kind of disguise. The heavily wrinkled washed beans are actually showing you the bean’s true cellular structure.

Appearance doesn’t equal quality. Sometimes, wrinkles are the most honest face a coffee bean can have, haha.

What Is Golden Honey Process Coffee? Specialty Coffee Processing Explained (White, Yellow, Red & Black Honey)

 Just recently, while attending a coffee tasting event—what we often call a “coffee cupping banquet”—I happened to hear the term “Golden Honey Process.” Most of us are already familiar with names like White Honey, Yellow Honey, Red Honey, and Black Honey when it comes to coffee processing methods. But what exactly is Golden Honey?

For a moment, it made me reflect on how new terminology constantly appears in certain industries today. These new terms often make people both curious and cautious. Are they the result of genuine technological innovation, or simply clever marketing? It struck me that this phenomenon is actually worth discussing within the specialty coffee world. So today, I’d like to share some of my observations and thoughts—and of course, feel free to join the conversation in the comments.

The charm of specialty coffee lies in its spirit of innovation and continuous learning. To some extent, the appearance of new professional terms and vocabulary in the industry is a good thing. After all, it means people are trying new ideas. These terms are often the result of both technical experimentation and marketing needs working together. That said, we should also approach them with a certain level of critical awareness rather than accepting everything at face value. My reflections today are simply based on this personal experience, and coffee processing methods are far from the only area where new terminology keeps emerging.

At its core, coffee processing is fundamentally about fermentation. During this stage, there are countless variables involved—temperature, humidity, time, microorganisms, shade, stirring frequency, and more. A farm or processing station might make subtle adjustments to traditional methods such as honey processing or anaerobic fermentation. For example, they might change the duration of anaerobic stages, alter the percentage of mucilage left on the beans, or modify the materials used in drying beds. In order to distinguish these slight variations from standard terminology, producers sometimes give the process a more specific and appealing name.

The coffee I encountered at the event was a Geisha from Costa Rica’s Finca La Bandera, processed using what they call the Golden Honey method. However, it’s important to understand that “Golden Honey” is not a globally standardized processing term. Instead, it is more of a marketing-level name proposed by a particular farm, processing mill, or green coffee trader. To truly understand what this means, we need to briefly revisit what honey processing itself actually is—and what the color labels added before the term represent.

Honey processing is a method that sits somewhere between natural (dry) processing and washed processing. The key step involves removing the outer skin and pulp of the coffee cherry while leaving some of the sticky, sugar-rich mucilage attached to the bean. The beans are then fermented and dried with this mucilage still present.

Different honey processes are categorized based on how much mucilage is retained and how the beans are dried:

• White Honey: Most of the mucilage is removed. Drying happens quickly, and the flavor profile is closest to washed coffee—clean and bright with crisp acidity.

• Yellow Honey: Some mucilage is retained. Beans are dried in the sun and turned regularly, producing moderate sweetness and body.

• Red Honey: More mucilage remains. Drying occurs slowly under shade or reduced sunlight, with less frequent turning, resulting in stronger sweetness, fuller body, and more noticeable fermentation notes.

• Black Honey: Nearly all mucilage is left on the beans. Drying happens extremely slowly under heavy shade with minimal turning. This produces the most intense flavors and body, often with dark fruit and spice notes—but it also carries the highest risk during processing.

  

So where does Golden Honey fit in?

In terms of technique, it can be understood as a finely calibrated point somewhere between Yellow Honey and Red Honey. Essentially, the farm has chosen to define what they consider an “ideal balance” within that range and has given it a distinctive name. By creating a new term within a familiar framework, producers can communicate the idea that their process represents a more refined and carefully controlled version of honey processing. In other words, they are signaling to consumers that this coffee is crafted using more meticulous techniques to achieve a particularly clean, sweet, and high-quality cup.

Golden Honey typically implies a more elegant sweetness and a cleaner fermentation profile, aiming to locate a superior or distinctive flavor point within the traditional honey-processing spectrum. At the moment, the term is almost exclusively associated with Finca La Bandera in Costa Rica. When people mention Golden Honey, they are very likely referring to beans from this particular farm.

Interestingly, I’ve also seen producers in Yunnan, China use terms such as “Golden Robe Honey Process,” which functions in a similar way. These names are essentially designed to create memorable branding and differentiation. In today’s highly competitive specialty coffee market, terms like natural, washed, and honey processing have already become basic vocabulary. When a new and distinctive name appears, it can instantly capture consumers’ attention and help a coffee stand out during green bean auctions or retail sales.

Of course, we can reasonably assume that a process like Golden Honey probably does involve more refined control within the existing honey-processing framework. For instance, the producer may aim to keep the mucilage at a precise “sweet spot,” implement strict drying management, and use slower drying at lower temperatures to prevent overly rapid sugar fermentation that could produce harsh acidity. The goal would be to develop a cleaner, more structured sweetness.

There may also be greater attention to even drying, including careful timing and frequency when turning the beans.

From a consumer’s perspective, however, it’s important to maintain a stable framework of knowledge. With solid fundamentals in mind, we can better evaluate any new terms that appear in the market. This helps prevent us from falling into certain consumerism traps. While innovation can certainly spark curiosity and encourage exploration, new terminology can also confuse consumers, making it difficult to determine whether something represents real innovation or simply old wine in a new bottle.

When tasting coffee, we should always remember that the most reliable judge is our own palate. When encountering a new term like “Golden Honey,” we can ask ourselves:

• Does this coffee truly taste different from other honey-processed coffees I’ve had?

• Is its sweetness, acidity, body, or clarity genuinely distinctive?

  

On the one hand, we should recognize that the industry is evolving rapidly and welcome innovation supported by transparent information. Such innovation reflects progress in coffee farming and provides new ways to communicate flavor experiences. On the other hand, we should remain cautious of names that are overly poetic, difficult to trace, or unwilling to explain their processing details. True innovators are usually happy to share the specifics of their techniques because they want people to appreciate and spread the value of their work.

After all, the definition of Golden Honey can vary from farm to farm, and there is no absolute standard. What we can develop instead is our own standard: no matter how beautiful the name sounds, let the flavor in the cup be the final judge. There’s no need to mythologize the terminology—always trust your taste buds to verify the most authentic experience.

Roasting Coffee Beans with a Hand-Cranked Popcorn Machine: Clever Hack or Dangerous Mistake?

 Not long ago, I came across a video online showing someone roasting coffee beans using a traditional hand-cranked popcorn machine—the kind we used to see on the street when we were kids, the one that would suddenly go BOOM behind you without warning. Honestly, that thing alone was childhood trauma for many of us. Of course, when used for coffee beans, there wouldn’t be that final explosive step. From a purely theoretical standpoint, this method does seem somewhat feasible. Still, I find it extremely unreliable in practice. So today, I want to take a closer, more serious look at this idea.

Traditional hand-cranked popcorn machines are actually somewhat similar to hand-mesh coffee roasting. Both rely on an external heat source—usually an open flame—to heat a sealed metal drum, allowing the contents inside to undergo physical and chemical changes. By manually cranking the handle, the beans can be agitated so they heat more evenly, reducing the risk of localized scorching. In principle, this isn’t all that different from how professional coffee roasters work. From a purely “can it cook the beans” perspective, yes—it can roast green coffee beans to a drinkable state. But to me, this method, much like hand-mesh roasting, comes with far too many uncontrollable variables and places very high demands on the operator’s skill. One small mistake, and things can go south very quickly.

As we all know, coffee roasting is a precise science. Different beans and different roast levels—light, medium, dark—require careful control of the temperature curve and the final endpoint temperature. With a popcorn machine, the temperature is neither measurable nor controllable. This makes it very easy to end up with beans that are burnt on the outside and underdeveloped on the inside—or worse, completely charred. Beyond temperature instability, timing is also extremely difficult to manage. Coffee roasting requires holding beans at specific temperatures for specific durations to properly develop flavor. A popcorn machine simply cannot provide that level of control. Roast time becomes entirely dependent on personal experience, and with so many variables involved, the outcome is highly random.

There’s also a critical safety concern that deserves special attention. When heating corn, popcorn machines build up internal pressure until the final “pop.” While coffee beans won’t explode like corn, they do release a large amount of smoke during roasting—mainly carbon dioxide and vaporized oils. If exhaust is insufficient, pressure can still build up inside a sealed container, creating a real risk of rupture or even explosion. On top of that, coffee roasting produces a lot of chaff, which is highly flammable. Professional coffee roasters are equipped with robust exhaust and cooling systems to handle this. A traditional hand-cranked popcorn machine, operated over an open flame in an open environment, dramatically increases the risk of chaff ignition or internal flare-ups.

Even if all of these risks were somehow managed through experience, roasting consistency would still be a major issue. Uneven roasting would result in inconsistent bean color, muddled flavors, and a pronounced smokiness in the cup. It would be nearly impossible to develop the elegant acidity, sweetness, and floral or fruity notes that make coffee enjoyable. Instead, you’re far more likely to get unpleasant defects such as smoky, burnt, rubbery, or bitter flavors. I’ve actually had coffee from small shops that intentionally use hand-mesh roasting—perhaps precisely for that smoky character. But achieving clean, pleasant flavors with such traditional methods is incredibly difficult. On top of that, post-roast cooling is absolutely crucial. A popcorn machine cannot cool beans quickly, allowing residual heat to continue roasting them and trapping dull, baked flavors inside.

So when you see videos like this online, I strongly advise against imitating or experimenting with them out of curiosity. Many content creators do these “wild” methods simply to make entertaining videos or chase traffic. In reality, using a traditional popcorn machine to roast coffee is both dangerous and inefficient, and it’s almost impossible to produce a truly good cup of coffee this way. If you really want to experiment with hands-on roasting, I’d recommend starting with a proper coffee roasting hand mesh instead. That’s how many enthusiasts begin. It’s inexpensive, but it requires practice—and good ventilation and fire safety are essential.

Finally, for anyone thinking about getting into coffee roasting: the real joy lies in fine control over flavor. And that inevitably means using the right tools. For your own safety—and for a genuinely good cup of coffee—it’s worth choosing a more appropriate and professional approach.

What Makes a Great Coffee Roaster? A Deep Dive into the Art & Science of Coffee Roasting

 Among coffee professionals, there is a group of true “behind-the-scenes heroes.” They may not be great talkers, many of them lean toward being introverts, and they tend to work with rigor, precision, and an almost obsessive attention to detail and data. In my eyes, they are among the most technically skilled people in the coffee industry: coffee roasters.

If I had to sum up their work in one sentence, it would be this:
“I am not the creator of flavor—I am a carrier of flavor.”
They are the ones who allow every coffee drinker to experience the unique character and terroir of different origins. In that sense, roasters play an irreplaceable role.

Looking back, I’m surprised that despite nearly ten years of daily writing, I’ve never written a dedicated piece about coffee roasters. Recently, as I’ve been testing beans from different roasters, I’ve found that I can genuinely sense their thinking through their roasting styles. This quiet, almost invisible form of dialogue has deepened my appreciation and respect for roasters—and that’s why I want to share my personal definition of what makes an outstanding one.

In the early years, whenever I attended coffee expos, I loved wandering through different halls to watch competitions. I’d marvel at the complexity of latte art designs, or cheer for the confident performances in barista championships. The atmosphere was always intense and electrifying. But when it came to roasting competitions, the scene was entirely different—almost silent. Roasters stood quietly by their machines, roasting beans, surrounded only by the rich, toasty aroma of freshly roasted coffee. Sometimes I couldn’t help but think: roasters are truly a group of people who can endure solitude.

They must integrate technical skill, sensory acuity, scientific thinking, and artistic creativity. Among all coffee-related roles, roasting may be the one that demands the most comprehensive set of abilities.

From my perspective, a solid foundation of technical knowledge is essential for any roaster. They need to be deeply familiar with the flavor profiles of different origins, varieties, and processing methods, and understand how physical characteristics such as green bean density and moisture content affect roasting outcomes. At moments like this, the old saying “Master math, physics, and chemistry, and you can go anywhere” suddenly feels very real—haha.

Roasters must also have a strong grasp of heat transfer (conduction, convection, radiation), the Maillard reaction, caramelization, and other physical and chemical processes. They need to adjust heat curves according to bean characteristics and master the logic and behavior of different roasting machines, whether direct-fire, semi-hot-air, or electric.

Beyond these technical foundations, roasters also need skills similar to those of baristas—most importantly, sharp sensory evaluation abilities. Through cupping—assessing dry and wet aroma, acidity, sweetness, body, and more—they must accurately judge roasting results and build a reliable flavor memory library.

Roasting one good batch doesn’t mean much. True mastery lies in consistency—producing good results batch after batch. We often judge a roaster by whether different batches of the same coffee taste noticeably different, which can even affect brewing parameters downstream. This shows just how critical roasting consistency really is. Developing standardized roast profiles that ensure stable flavor across batches while meeting commercial production demands is one of the core competencies of an excellent roaster.

If everything above represents “hard skills,” then the following are the “soft skills” that truly differentiate roasters at a higher level. Whether baristas or roasters, when working with a non-standardized product that people consume, the ability to flexibly apply knowledge in real-world situations becomes crucial. Being overly dogmatic or ignoring the relationships between variables can turn an inherently exploratory craft into something rigid and stagnant.

Many outstanding roasters seem to enjoy solitude—or at least quiet focus. They must possess patience and deep concentration, enduring repeated testing and adjustment. It may take dozens of trials to find the optimal roast profile for a single coffee. They spend long hours monitoring the roaster, remaining highly sensitive to details such as first crack sounds and color changes.

Whenever I visit roasting facilities and happen to see a roaster at work, even watching through a glass wall, I can’t help but feel that the end of roasting is… loneliness. It’s truly demanding work.

That said, roasters also need strong communication and collaboration skills. Some younger roasters may fall into the trap of working in isolation—focusing solely on roasting without engaging with the outside world or paying attention to industry trends. That’s a dangerous path.

Data-driven decision-making—using roast curves and cupping scores—combined with the courage to experiment with new processing methods and blending strategies is essential. With innovative processing techniques constantly emerging, roasting faces new challenges all the time. Staying informed about industry trends and understanding shifts in consumer taste preferences should be a conscious, ongoing habit.

Another crucial scenario is custom roasting. Many roasters work closely with partners to create tailored roast profiles. This customization isn’t just about exclusive blends or unique roast curves—it’s about understanding brand positioning, target flavor profiles, and balancing cost, efficiency, and flavor. In commercial roasting, profitability must also be considered. Creating a distinctive roasting style that gives a brand a recognizable identity requires roasters to be adaptable, business-aware, and committed to continuous learning.

In fact, many roasters are also “coffee hunters,” traveling to origin countries, working directly with farms, and participating in quality control from cultivation through processing.

An outstanding coffee roaster is both a scientist and a craftsman. They connect producers and consumers, serving as a core creator within the coffee value chain. Roasting is never just about making beans “done.” It is a long-term pursuit that demands dedication, passion for flavor, and a commitment to constant refinement.

This piece reflects only my personal perspective and appreciation. I can’t possibly list all the qualities that make roasters exceptional. But I do know this: they deserve far more recognition. When we taste a cup of coffee, we should try to sense the quiet effort and unspoken care of these behind-the-scenes heroes.

To all the coffee roasters out there—you are truly amazing. Thank you for being here, for filling my life with good coffee, and for enriching it in ways that often go unseen. 

How Do Coffee Bean Density and Brittleness Affect Grinding and Flavor?

 Introduction:

Anyone who’s ever used a hand grinder knows this feeling well — some beans grind effortlessly, while others feel like a full-on workout. Why does that happen? Today, let’s uncover the mystery behind it.

When it comes to grinding coffee, there are many factors to consider — origin, processing method, roasting level, and brewing technique. Each of these elements affects how coarse or fine the coffee should be ground for optimal extraction. However, even when using the same grinder, some beans are noticeably harder to grind than others. So, what makes certain coffee beans tougher to grind?

---

1. Exploring Bean Brittleness

Before we go further, it’s important to distinguish between density and brittleness — two terms that are often confused but mean very different things.

Density refers to the weight of a single coffee bean divided by its volume. In most cases, we talk about bulk density, which is the weight of a container filled with coffee (minus the container) divided by the container’s total volume.

Generally speaking, higher-density coffee beans tend to contain more sugars. Beans grown at higher altitudes and cooler temperatures develop more slowly, giving them more time to absorb sugars from the surrounding fruit. High density is often associated with better coffee quality.

However, density alone doesn’t determine how easy a bean is to grind — that’s where brittleness comes in. Brittleness changes during the roasting process. For example, it’s nearly impossible to grind raw (green) coffee beans with a standard grinder, while dark-roasted beans break apart with ease.

Raw coffee beans have a tightly packed cell structure. On a microscopic level, their vacuoles (tiny membrane-bound chambers containing nutrients and water) are extremely strong and resilient.

During roasting, however, moisture evaporates and the cell volume expands. The resulting air pockets weaken the structure, making the beans more brittle. In general, there’s little direct correlation between density and brittleness.

2. How Roasting Affects Brittleness

Roasting has the greatest impact on coffee bean brittleness, as it causes dramatic changes in cell structure.

Inside the roaster, heat and airflow dry out the beans, reducing moisture and making the cell walls more fragile.

Different stages of roasting affect brittleness in different ways:

• Coffee just past the first crack (the stage when beans rapidly expand and lose moisture) has an average particle size of around 305 microns after grinding.

• Coffee after the second crack (when oils begin to migrate to the surface) has an average size of 120 microns.

  

This means the longer the roast, the higher the brittleness.

Roasting impacts both density and brittleness. As beans lose water and organic material, they become lighter but also expand in volume. This results in a lower density as roasting progresses, revealing a subtle connection between a bean’s density and brittleness.

3. What Does This Mean?

As roasting continues, beans lose weight and moisture, and their cell walls weaken.

This means that under identical grinding conditions, dark-roasted beans are easier to grind than light-roasted ones. They also tend to extract more easily and quickly. During deep roasting, aromatic compounds, sugars, and acids become more volatile.

Darker roasts are more soluble and often exhibit bolder, more traditional coffee characteristics. Because aromatics and sugars are more volatile at this stage, extraction happens faster. That’s why a coarser grind setting often works better for dark roasts.

4. How Does This Affect Grind Size?

When grinding coffee, particle size is one of the most important considerations. Understanding the roast level and brittleness helps you achieve your desired flavor profile.

Lower solubility and brittleness in lighter roasts mean they should be ground slightly finer to allow for better extraction of aromatic compounds.

Since light-roasted beans are less brittle, they also take longer to grind. The difference might seem small, but when you’re making espresso, it becomes noticeable.

Fortunately, you don’t need to worry about losing aroma during this slightly longer grinding time. The process only takes a few minutes (or just seconds with a commercial grinder), and aromatic compounds remain intact for about five minutes after grinding. However, if coffee sits ground for too long, its liveliness and complexity quickly fade.

From a grinder maintenance perspective, brittle beans cause less wear, while light roasts can dull your burrs faster. On the other hand, dark roasts tend to produce more fine particles, which can clog your grinder and lead to uneven extraction.

---

Final Thoughts

Although most people don’t think much about bean brittleness, the science behind it is fascinating. Next time you brew coffee, take a moment to notice the roast level and adjust your grind slightly to match it.

After all, the secret to brewing great coffee lies in the subtle, mindful adjustments you make along the way.

Where Do the Crackling Sounds in Coffee Roasting Come From?

 Roasters frequently hear crackling sounds when roasting beans. Where do these crackling sounds originate, and why do they occur?

Coffee roasting is the process of placing green coffee beans in a heat-resistant vessel and applying heat, which causes a series of physical and chemical reactions both inside and outside the bean. During this process, various flavors, such as acidity, bitterness, and sweetness, are generated, and the coffee's body (mouthfeel) and color are developed, transforming the green beans into dark brown roasted beans.

The crackling sounds in coffee roasting are the result of the pyrolysis process occurring during the coffee bean's "First Crack" and "Second Crack." Taking a heat-resistant green bean as an example, the First Crack begins around the 7-minute mark and lasts for approximately two minutes. This sound is low and dull, signifying the onset of pyrolysis, the caramelization of starches, moisture evaporation, and the release of internal gases. The Second Crack typically occurs around the 12-minute mark, producing a violent, sharp sound, which indicates the fracturing of the cellular structure as the roast progresses deeper.

The First Crack occurs when the internal temperature of the coffee bean reaches 200℃, causing the release of internal steam. The First Crack for all the beans typically ceases after about two minutes.

Following the First Crack, certain newly formed components begin to decompose while simultaneously generating heat. When the internal temperature of the bean reaches approximately 230℃, internal gases are released again. This gas generation causes the bean to further expand. Along with this expansion, the cell structure is fractured once more, immediately followed by another cracking sound. This is known as the "Second Crack" (and rarely, a "Third Crack").

The First Crack is the sound roasters intently look for during the roasting process. Once the First Crack occurs, the roaster's control over heat and time becomes exceptionally important, as any adjustment can definitively affect the flavor profile of the batch. The First Crack serves as both a reminder and an indispensable element for flavor development, and it involves not only physical reactions but also chemical transformations within the coffee bean. Listening to the sound of the beans rolling and the density and intensity of the cracking sound helps guide the roast. The First Crack sounds similar to popcorn popping, and it is generally louder than the Second Crack, which is often described as sounding more like Rice Krispies cereal dissolving in milk.