When coffee is roasted, it undergoes a number of chemical changes that can be distinguished by various sensory cues. For specialty coffee roasters, it’s important to pay close attention to these cues in order to achieve a desired flavour and aroma for their coffee.
Two of the most distinctive indicators of how beans are changing during the roast are the temperature thresholds known as first and second crack. The two “cracks” are named for their audible popping sound, and typically occur at 196°C and 224°C. To this day, they are used by roasters to reach a target roast profile and develop flavours in the right way.
To understand more about cracks in coffee roasting and their importance in flavour development, I spoke with South African Barista Champion and MTPAK Coffee Ambassador, Ishan Natalie.
What Is First Crack?
During roasting, coffee beans undergo a series of chemical reactions as a result of heat transfer, known as endothermic and exothermic reactions.
Endothermic reactions are when the beans absorb heat energy from the drum. In the initial stage of a roast, the heat moves from the roasting environment into the green bean. This initiates a reaction between the amino acids and reducing sugars (called the Maillard reaction), which creates a range of flavour and aromatic compounds within the beans.
The Maillard reaction accelerates between 120°C and 150°C, before slowing down when the bean temperature reaches approximately 170°C, giving way to caramelisation.
Caramelisation is a form of pyrolysis (chemical decomposition as a result of heat) that decreases sweetness and increases bitterness in the beans. Up until this stage, the beans have been absorbing heat energy and building up internal pressure.
At around 196°C, the beans will emit a cracking sound from within the drum, not unlike the sound of corn kernels popping. This is called “first crack”.
At this stage, the beans enter an exothermic reaction, releasing built-up energy, steam, and carbon dioxide (CO2) from their core. They spontaneously expand and expel chaff, and start to give off smoke. During this time, the bean surface temperatures decrease for a brief period as water rapidly escapes the beans – a phenomenon known as the “endothermic flash”.
Ishan Natalie has worked in the coffee sector for more than two decades. Alongside his work as a consultant for Starbucks in South Africa, he’s also competed in several barista competitions across the world, winning three National Barista Championships, among others. He tells me a lot of specialty roasters use first crack to guide the final steps of their roast.
“[Many specialty coffee] roasters finish their roast shortly after first crack, as this brings out the nice, bright, natural characteristics of the coffee,” he says. “However, sometimes, very light roasted coffee might taste sour. Whether you should stop soon after first crack or continue for a while longer largely depends on the preference of your customers.”
When monitoring the roasting process, it’s important to note that first crack is defined as the point when all the beans in the chamber begin to crack, rather than just the first few beans.
What Is Second Crack?
After the first crack, a short endothermic phase follows. The colour of the coffee continues to darken, while gas and pressure start building up within the bean once more.
During this phase, the cellulose structure of the bean continues to break down and becomes more brittle, paving the way for a second crack. Ishan tells me that the beans will also start developing more sweetness.
When second crack occurs (typically around 224°C) the oils within the coffee beans start to migrate to the surface. The roasting smoke also becomes darker and more pungent. This is characteristic of dark roast profiles.
It’s important to carefully monitor this stage of the roast as the character of the beans begins changing at a rapid rate; if left for too long, they may even ignite.
Roasting too deep into second crack will mask even the stronger and more distinctive flavours of your beans. Instead, they will start to taste burnt and smoky, with muted acidity. Later after a second crack, they can even start to taste like charcoal as the body of the coffee decreases.
In The Coffee Roaster’s Companion, Scott Rao says that while the primary cause of first crack is the buildup of steam pressure, the accumulation of CO2 is the main driver of second crack.
When Should Roasters End Their Roast?
The point at which you choose to end your roast will depend on the roast profile you are trying to achieve. Darker roasts are sweeter and have a more traditional “roasty” flavour, while lighter roasts are more acidic and often sought-after among third wave coffee consumers.
For example, roasters who want to create an espresso blend may extend the amount of time after the first crack to increase development of the bean core.
In his book on home coffee roasting, Kenneth Davids makes clear distinctions between the roasting that ends shortly after first crack compared to after second crack.
“Roasting that finishes a short time after first crack will usually result in a cup that’s acidic and sweet, but also tealike,” he says. “On the other hand, roasting until shortly after the second crack will often give rise to a balanced, dark roast cup without acidity; it will be pungent, yet sweet and full-bodied with a roasty flavour.”
For specialty coffee roasters, settling on a target roast profile can sometimes be difficult. Ishan tells me that it’s important to think of the end consumer and the way in which they’re most likely to consume the coffee.
“I would suggest conferring with a barista,” he says. “Baristas are the experts, they know which flavours customers enjoy and should be able to offer advice on how they like to drink their coffee once it’s been roasted.”
By working closely with baristas, Ishan says that roasters can tweak the roasting process to bring out a target flavour based on their customers’ preferences.
“Roasters should take the time to step behind the bar and dial in the coffee to see how it tastes, both as an espresso and with different types of milk. I’ve tried many soft sweet stone fruit coffees on the cupping table that ended up tasting like molten chocolate as espresso,” he adds.
Once a roaster has settled on a roast profile, they must ensure their coffee arrives at the café or consumer as fresh as possible. It’s important to note that, for instance, beans will degas at different rates depending on their roast profile. Dark roasts, for instance, have greater internal pressure than light roasts, and will degas more quickly as a result.
Irrespective of roast profile, roasters should include a degassing valve on all coffee packaging to allow the built-up CO2 to escape from the coffee packaging without letting oxygen in.
Packaging should also communicate information about the roast, such as the roast date, roast profile, and flavour notes.
“Packaging should list the best ways to brew coffee in addition to the flavour characteristics,” Ishan says. “The brew method [can] differ depending on the roast profile, so it’s important to include this for the end consumer.”
For specialty coffee roasters, it’s crucial to know what first and second crack indicate during the roast. They represent key milestones in the flavour development and roast profile of coffee beans. Once a roaster has decided on their target roast profile, however, guided by these milestones, it’s important to choose the right packaging for their roasted coffee.
At MTPak Coffee, we offer a range of sustainable packaging that caters to everything from espresso blends to light roast single origins. We work closely with roasters to design packaging that best communicates the distinct flavours and aromas of their coffee, as well as information on the roasting and brewing methods.