Aillio Bullet R1 / R2 的初裂和發展：DT、DTR 和最終溫度

After First Crack, small changes in heat and time can quickly change the final flavor of a roast. On the Aillio Bullet R1 / R2, I pay close attention to how First Crack begins, whether the RoR remains continuous, and how development time (DT) relates to end temperature.

Rather than treating DTR as a fixed target, I use it only as one reference within the larger roast progression. This article explains how I make these decisions during the final stage of the roast.

In RoasTime, once we press the First Crack (FC) button, the software labels the period from First Crack to drop as Development.

Why does coffee make a cracking sound during roasting?

Before First Crack, the evaporation of the coffee bean’s original moisture, water formed through Maillard and caramelization reactions, and CO₂ and other gases produced through thermal decomposition and decarboxylation all contribute to increasing internal pressure. As this pressure builds, the coffee bean expands. When the internal pressure and structural stress exceed what the bean tissue can withstand, the structure ruptures, producing the sound we recognize as First Crack.

I usually press the button when I hear the second cracking sound.

The following conditions may make First Crack difficult or impossible to hear during roasting:

1. Lower green-bean density or hardness
2. Natural-processed or anaerobically processed coffees
3. Dehydrated or aged green coffee
4. An excessively long roast. Water vapor inside the bean may gradually escape through the cellular structure, preventing enough internal pressure from building up quickly enough to produce a distinct crack.
5. First Crack occurs at a higher temperature than expected. We may think the coffee is not going to crack when, in fact, First Crack simply has not happened yet. I have found this more likely with coffees that are relatively dry on the outside but still retain more moisture internally. Some specially processed washed coffees often behave this way.*
6. Machine noise or a very small batch size

*Coffees that are relatively dry on the outside but wetter inside are among the most difficult coffees for me to roast. They also require a particular roasting approach, which I will explain in the Member’s Section.

In addition, if the same batch contains beans with inconsistent size, density, moisture content, or maturity, First Crack may become scattered and prolonged rather than occurring as a clear, continuous series of cracks.

If I cannot hear First Crack, there are several other ways I use to identify it. Here are some references you can use:

How to Identify First Crack When You Cannot Hear It

I do not use the trier to smell the coffee and determine when First Crack occurs. The reactions after First Crack progress too rapidly, and there is simply very little time to pull the trier and evaluate the beans. This is especially true with natural-processed coffees, where the temperature can change very quickly and even a small delay can easily lead to overdevelopment.

There is also a practical limitation: if I have a cold and temporarily lose my sense of smell, I cannot rely on aroma as a roasting indicator.

The questions can also be like this: Can Coffee Still Taste Good Without an Audible First Crack? Not necessarily. The coffee needs to be brewed and tasted before we can determine whether heat actually travelled to and affected the layers it needed to reach.

This can happen with green coffee beans that are relatively dry on the outside while still retaining more moisture internally. Even if the IBTS shows that the outer layers have reached a temperature at which First Crack would normally occur, the outer layers may be too dry to generate enough steam pressure to rupture the bean. At the same time, heat may not yet have penetrated deeply enough to turn the moisture inside the bean into sufficient steam to break through the outer structure. As a result, no audible First Crack may occur.

I have experienced roasts like this myself, and some of them tasted perfectly fine when brewed. This is why consciously managing heat transfer and moisture release is so important. If we focus on controlling heat transfer and moisture release rather than simply chasing numbers, then even when a roast produces no audible crack and does not taste good, we have a framework for understanding what may need to be adjusted in the next batch.

The condition of the green coffee is not the only reason a roast may produce no crack sound. Some roasters deliberately roast coffee without an audible First Crack.

A coffee company in Taiwan, Lab 19 Coffee Roasting, has developed its own “No Crack (NC)” roasting approach, in which no cracking sound is heard during the roast. They describe the resulting coffee as:

Fuller and more structured in flavor. Sweetness is significantly enhanced, particularly in fresh fruit notes and hard candy like sweetness.

According to their article, it is written:

With the same coffee, our conventional profile might reach first crack at around 200°C on a Loring S7 and finish at 204°C. With NC roasting, we typically drop out the beans at around 197 to 198°C.

It is important to note that they use a Loring, which is very different from an Aillio Bullet. I do not recommend deliberately attempting a no-crack roast on the Bullet, as the risk of underdevelopment is much higher. In the Member’s Section, I will discuss some of the possible reasons why a no-crack approach can work.

One thing to keep in mind is that caramelization toward the later part of the roast causes sugars to break down. In the early stages of this degradation, a significant amount of acetic acid can be formed. This is one reason why, around First Crack, the aroma can shift from grassy or grain-like notes toward a noticeably acidic smell. It is also one of the reasons light-roasted coffee tends to taste more acidic.

As the roast continues, sweetness gradually becomes more pronounced. If too much heat is applied, or if the roast continues for too long, terroir expression gradually decreases and woody or bitter flavors may begin to appear.

Adjusting the balance between acidity and sweetness is usually approached by adjusting development time (DT).

This table is only intended to give readers a quick sense of the typical trend. In some cases, even with a short development time, the bean core can still be fully developed. If the core is fully developed, the coffee will not necessarily taste overly acidic.

End temperature is one of the most direct factors affecting weight loss. A higher end temperature generally means that the outer layers have lost more terroir expression. The coffee may show more obvious flavor intensity shortly after roasting, but its shelf life may also be shorter.

This is similar to what I discuss in “Direct-Fire Roasters and Clay Pots Are More Likely to Cause Flavor Loss.” In both cases, the result comes from exposing the coffee to higher thermal energy during roasting.

If I had to choose only one, I would choose development time (DT).

When everything in the roast is progressing normally, the coffee should reach the desired end temperature at roughly the same time that the development time reaches the expected duration. However, if one reaches the intended target while the other has not, I prioritize DT. The more common situation is that the end temperature has already been reached while the DT is still shorter than expected.

I would rather have a coffee be slightly overdeveloped than underdeveloped. A slightly overdeveloped coffee can still be drinkable, whereas an underdeveloped coffee may be difficult even to drink. The body naturally reacts negatively to coffee that tastes too raw. In addition, the market is already quite accustomed to coffees that are somewhat overdeveloped, so leaving the beans in the drum slightly longer is unlikely to cause a strong negative feedback from most consumers.

The downside of slight overdevelopment is that weight loss (WL) may be somewhat higher. The coffee can taste very good shortly after roasting, but it may also have a shorter shelf life.

Both overdeveloped and underdeveloped coffees can improve significantly after an appropriate resting period. However, as professional roasters, we should try not to allow these kinds of abnormalities to occur in the first place.

DTR stands for Development Time Ratio

Scott Rao describes DTR as “not a guarantee of development,” but only “one of many indicators of how a roast progressed.” He also warns that when a roast contains a crash and flick, attributing baked, underdeveloped, or roasty flavors to DTR alone misses the larger problem. In my view, this is because development time continues to accumulate even when the progression of heat has already changed.

I believe DTR is meaningful only when the progression of heat into the deeper layers of the coffee remains continuous. In other words, there should not be a crash. Once the RoR crashes, the roast may begin to behave more like a relatively dry roast of the outer layers. I explained this briefly in “What Is a Stalled RoR or Baked Profile?”

Personally, I do not spend much time looking at DTR. I pay much more attention to ambient temperature, the type of coffee, and the overall roast plan. In practice, I find these far more useful than DTR. I will explain the detailed planning process in the Member’s Section.

With washed coffees, the RoR can crash very easily after First Crack, so this is something I watch closely. Once a clear crash has occurred, there is usually very little that can be done to fully recover the roast. Even aggressive adjustments afterward may not be enough to restore the original heat progression.

For this reason, the overall roast plan and targeted thermal management before you start to put your beans into the roasting machine are especially important. In “How to Roast on the Aillio Bullet R1 / R2 Coffee Roaster,” I outline the main factors that should be considered before and during the roast.

The Roast Continues After Drop

Coffee beans still retain heat after leaving the drum. Faster cooling helps preserve the roast endpoint you intended.

View the Cooling Tray