First crack: it’s a moment that has been given almost mythical status in coffee roasting – and it deserves it. A key stage in any roast, understanding it will give you insight into how flavours and aromas are developing.

Let’s take a look at what first crack is, how you can recognise it, and what this means for your coffee beans.

Spanish Version: ¿Qué es el Primer “Crack” y  Cómo Reconocerlo?

Steam building up inside the coffee bean leads to first crack. Credit: Angie Molina Ospina

What Is First Crack?

First crack is the moment when coffee beans begin to approach edibility. Coffee goes through two “cracks” when roasting, and light to medium roasts will finish somewhere between them. Dark roasts will typically be roasted past second crack. (However, if only the first few signs of second crack have started to appear, it will probably still be closer to a medium roast.)

So what actually are first and second crack? Audible, physical cracks. (In fact, Barry Levine of Willoughby’s Coffee & Tea compares them to hearing popcorn popping.) They happen because the coffee bean has expanded and its moisture begun to evaporate. This moisture forms steam, and then pressure, that forces the beans to crack open.

Joe Behm, CEO and founder of Behmor, tells me, “When you start to detect the aroma changing from baked bread to caramelized sweetness, you know the sugars are developing and first crack is about to begin.” He tells me that this change in aroma is “like a bell getting ready to go off”, letting him know that he needs to be thinking ahead to the end of the roast.

It’s important that the roast doesn’t begin to stall at this period: delays can result in baked coffee, a roast defect that creates a doughy cup profile. So let’s take a closer look at what’s happening, and how you can see when first and second crack are approaching.

Colour change is only one of several physical changes during roasting.

Time to Talk About Heat

As heat is applied to the coffee beans, they go through endothermic and exothermic reactions. Up until first crack, the beans absorb the heat (an endothermic reaction). The moisture dissipates and the colour changes from green to yellow and then brown. The aroma will be cereal-like: think toast, popcorn, or grass.

As for first crack, this is a brief exothermic reaction: the beans release heat (energy) in the form of that steam we mentioned above, along with carbon dioxide. The bean will have doubled in size and shed the majority of their silverskin, but oils won’t yet be present.

After first crack, it switches back to an endothermic reaction until second crack, the final exothermic reaction (if you choose to roast your beans that far).

As well as checking colour change, roasters should pay attention to other visible signs – such as swelling.

SEE ALSO: Everything You Need for a Home Roaster Starter Kit

Flavour Development

Although we like to talk about first and second crack when roasting coffee, it’s important to remember that coffee flavour profiles are the real goal. And for this reason, we also need to consider caramelisation and the Maillard reaction.

Both of these happen before first crack. The Maillard reaction occurs when we start to see browning, and it creates many of the flavours in our coffee – especially the savoury ones.

As for caramelisation, it happens a little after the Maillard reaction. Joe Marrocco of Mill City Roasters describes it as the dehydration of sugars through heating, which then give off the carbon dioxide and H2O that cause first crack. As you may have guessed, this process leads to caramel flavours in the roast – but it’s also what causes bitter notes if the heat continues for too long.

It’s hard to predict exactly when these reactions will take place. Joe tells me that they occur as a result of the amino acids and sugar molecules, and as these break down, hundreds of reactions occur. These reactions start at different temperatures, but, due to different coffee structures hitting these different temperatures at different times in the drum, they can overlap. Since it’s so difficult to anticipate these reactions, it’s even more important to pay attention to the aroma and colour of the beans.

Pay attention to the physical signs of roast development. Credit: Jesper Alstrup

Why Is First Crack Important?

Coffee beans go through an immense amount of physical and chemical transformations at every stage of the roast. In fact, we still do not understand many of these changes. And of those that we do understand, some are easy to detect but others are not.

First crack is, in fact, one of the easiest stages to spot. However, it’s also useful to anticipate when it’s approaching – and to understand what else is happening to the beans. This will give you better control over the roast and ensuing flavour profile.

So next time you try roasting, pay attention to the development of the aromas as well as the roast colour. Look for development in bean size and shape. And remember that it takes a lot of time, experimentation, and research to become a good roaster – but it’s always worth it when you taste the final cup.

Please note: Behmor is a sponsor of Perfect Daily Grind, and they approved of this article topic. All of our interviewees receive a copy of the relevant article prior to publication, but Behmor have had no sway over the final copy.
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