First Crack FAQ: What is First Crack? What is Second Crack?

If you’re struggling to identify the sound of first crack and second crack when roasting coffee, read on…

I remember many years ago writing a post about roasting, with the advice to “lower the temperature just before first crack.” Someone commented, “how are we supposed to know what we are supposed to do when the thing we are supposed to react to hasn’t happened?”

I’m sure I wrote something back about “experience and anticipation” … but I knew it’s like tossing a curveball of an answer. How do you tell someone to “do something in anticipation of something that’s about to happen, but do that first thing just a bit before the second thing actually happens”. That’s a bad sentence and a bad concept. Luckily it’s just coffee.

And I hate to say it but you will indeed learn to anticipate that thing that’s about to happen, with experience. How will you do it? With your senses: sight, smell, sound … and a good thermometer too. Let’s start with some definitions though.

Roast Cupping Test – Sample 7, End of 1st Crack 412f – City roast. Thompson Owen, Sweet Maria’s Coffee Panama Boquete La Camiseta

What is First Crack?

Here’s the short answer: First crack is the sound coffee makes when it reaches about 395 to 405 fahrenheit (external temperature). It cracks because the water trapped in the bean creates pressure as it turns to steam.

What is Second Crack?

The basic answer is around 440 to 455 fahrenheit (external temperature), the buildup of Carbon Dioxide in the bean becomes too great for the increasingly brittle bean structure. Again the expansion causes an audible crack or snap.

What is First Crack, in more depth please?

Coffee is a dried seed, but has residual moisture in it of roughly 10-12%. In the roast process the coffee requires a lot of heat in the “drying phase” when the coffee turns from green to yellow to brown. When the internal temperature of the bean rises, the water bound up in the coffee is transformed to water vapor, that is, steam. As the moisture forces itself out of the coffee bean, we hear the first crack, a popcorn like sound, and can often see moisture leaving the coffee. Physically the bean enlarges and the crease in the middle may open up somewhat. As it opens, it can let go of the silverskin that was pinched by it, chaff. First crack is not solely due to the pressure from water vapor, but it is the main driver. Up until first crack, the dynamic of coffee roasting is considered endothermic, meaning that heat must be applied to the coffee to absorb in order to force the desired changes. First crack marks a shift, where coffee goes from being endothermic to exothermic as the energy balance switches, and rate of change in the bean can increase dramatically.

In more detail, what is Second Crack?

While the coffee roasting process is continuous, people who roast focus on the audible cues of 1st crack and second crack. While First Crack is driven more by the change from water to water vapor, second crack’s audible snap is the result more of Carbon Dioxide gas pressure ( as well as CO and N-2). After an initial release of gas along with steam in First Crack, pressure builds up quickly once again. And this time the bean structure consisting largely of cellulose plant material (like tree wood) has become more brittle. So second crack has a different sound, more of a snap, like when you add milk to Rice Krispies cereal. Second crack can fracture that cellulose matrix in a way that oils and gasses find it easier to migrate to the surface of the bean, or out of the bean completely.

Roast Cupping Test - Sample 9, City+ roast 432f
Roast Cupping Test – Sample 9, City+ roast 432f – Nearing second crack, but not there yet. Panama Boquete La Camiseta

How can I hear the difference between First Crack and Second Crack? Just listen …

I have said that First Crack sounds more like popcorn popping, and second crack sounds more like puffed rice cereal when you add milk, it snaps. That might not mean much to some people though. And in fact first crack is NOT exactly like popcorn (I hope, because the rapid popping of popcorn would mean a terribly fast roast)…

So I created a rough audio guide to the sound difference. Here’s my narrated tour of the cracks in an air type roaster …Have a listen:

What do the cracks sound like? First Crack and Second Crack Audio

Here are some alternate recordings I created in the past. This is First Crack of a wet process coffee in an air roaster, no narration. Exciting stuff! :

First Crack Audio File – Wet process coffee

and First Crack of a Dry Process coffee, also in an air popper, which can sometimes be quieter and more slow-paced:

First Crack Audio File – Dry process coffee

How else can I tell the difference between First Crack and Second Crack?

Besides the sound of first and second crack, there should be other clues. I don’t want to sound dumb here, but, well, first crack comes first, and second crack comes second. Before I lose you, the problem isn’t temporaly dyslexia here … it’s that in some rapid roast processes like an air popcorn popper they can blur together. Also, some coffees have more pronounced or subtle sounds. Older, past-crop coffee can have a very loud sound to first crack. Some dry process coffee can have a very subtle first crack sound, and I have even roasted some that seem to make no sound at all.

So in case you miss the audible cues to First or Second crack, here are some other things that help. They are not always true …but can often be true:

  • A coffee bean can look more patchy in color, with light and dark areas, during first crack, whereas by the time second crack is under way it will have more even surface color in a single bean.
  • The bean-to-bean- color variation should be farm more uniform in second crack.
  • If you could take out coffee from the roast and study it, there are subtle differences. Just before first crack the crease in coffee is usually tightly shut, and the edges around the flat side of the bean are sharper and more angular, After it enters first crack the crease can open slightly, the bean expands a bit, and as it does the edge appears slightly more round. See the photo below! As coffee heads into second crack the it has expanded more, and this should be a clear difference you can observe.
  • Second crack can seem more rapid than first crack.
  • In an air roast, much of the chaff has come off by the time the coffee has entered second crack. (Dry process has far more chaff, so this is less true with those coffees as it continues to release chaff for longer).
  • First crack does not have the same pungent roast aroma as second crack does.
  • The smell of first crack is more like grain, like bread baking, whereas second crack has more pungency.
  • In the early part of First crack you might actually feel some moist steam coming from an air roaster. The air coming out in second crack feels very dry.

What does First Crack look like?

The subtle difference between coffee that is just about to enter 1st Crack, and coffee that has entered it.
The subtle difference between coffee that is just about to enter 1st Crack, and coffee that has entered it.

If you could take out coffee from the roast and study it closely, there are subtle differences. Just before first crack the crease in coffee is usually tightly shut, and the edges around the flat side of the bean are sharper and more angular, After it enters first crack the crease can open slightly, the bean expands a bit, and as it does the edge appears slightly more round. (PS- I didn’t note the coffee this was in the image, but it might have been a honey-process or natural).

What does Second Crack Look Like?

I think I can answer this best by inserting a video I just made, covering first crack, second crack and the changes in appearance associated with each. I titled it: Coffee Class: First Crack, Second Crack, Coffee Roasting Development . I cranked out this video, geared toward the home roaster who can’t get enough info about the changes in the coffee bean during first and second crack. Ok – it’s not that little, it’s 34 minutes! This is a basic non-sciencey presentation to show how coffee changes in roasting, and what sounds and sights to expect.

Unfortunately the roaster is a bit noisy in the middle parts, but there is a lot of little nuggets of information in this presentation of nearly 35 minutes! Less than perfect, this video still has some good information.


Checking Roast Levels with Ground Samples

A great way (after the fact) to compare roast levels is to check the roasted whole bean appearance versus the ground appearance. The ground color can be easier to judge. Below, the first whole bean photo is the same roast ground in the second, and the third photo is same as the fourth.

First Crack FAQ … and Second Crack Too!

If there are questions you would like to see added, or clarifications you need to the ones below, please add a comment at the bottom of the page and we will address it. This is a work in progress!

(When I am referencing temperature in these questions, I am referring to the commercial shop roasters I have used. Temperature measurement in different roasters varies, based on thermometer placement, type, roaster type etc. So it can be hard to correlate roast temperatures from one instance to another. Use the numbers as a rough guide and check them against your own settings).

What time does first crack happen in the roast?

There is no set time that first crack occurs. Every roast machine or process is different. The range in roast times from green to first crack can be huge on different types of roasters. There are commercial roasters that can reach first crack in 45 seconds! And there’s a roast style in some Mediterranean locales where they roast 30 minutes or more until first crack! But to give a general range for home roasters, a small air roaster /popper can have a range of 3 to 7 minutes to first crack. A home drum roaster like the Behmor can be 10 to 12. Many small shop roasters of the 5 – 12 Kg capacity range reach 1st crack in 9-12 minutes. For quality, there is no “correct” timing for first crack. It depends on the type of thermal transfer, the batch size, the coffee, ambient temperature, and many other variables.

When does second crack happen?

Well, the short answer is, after first crack! Second crack should start after a pause of roughly 30 seconds to 4 minutes after first crack ends, with many roasters. Some fast roasters can merge first and second crack, which makes it confusing to make roasting decisions. But with most roasters that are not introducing too much heat during first crack, there should be a distinct pause before second crack starts. The “popping” of the coffee becomes more of a “snapping” sound like adding milk to Rice Krispies cereal (listen to my audio recordings above!) In some air roasters / poppers you can reach second crack in 6 minutes, whereas in a drum shop-size roaster you should see second crack just start in a range from 14-18 minutes.

What does it mean when first crack is very loud?

I have noticed that when green coffee is older, or more dried out, it can have a more percussive and louder first crack. So it might be a quality issue with the coffee. It also seems that less dense coffee, often lower grown, can have a louder first crack. (Conversely we have had some high grown dry-process coffees that have a very quiet and short audible first crack!)

At what temperature does first crack happen?

In my experience with temperature probes that directly contact the coffee, this will happen at 395 to 405 fahrenheit (201-208 C roughly). But like all things in roasting, there are no simple answers! We can’t measure the internal temperature of the bean with a probe, which would be the most consistent measurement. And most ways to measure temperature are not strictly reading bean surface temperature … there’s always some environmental influence. It also varies based on altitude. (You may also notice that, if first crack is water turning to steam, these readings are 2x the boiling point of water generally! But water vapor and boiling point are different, and dependent on other factors like pressure.)

What temperature does second crack happen at?

With the same probes I referenced above for first crack, second crack happens at a range of 438 to 450 fahrenheit (225-232 C). It has seemed to me that second crack has a more variable temperature range based on the coffee. Still, these numbers can only be contextualized by the type of roaster, type of probe, and positioning.

Do we say a coffee is “in first crack” when I hear the very first pop?

No. There is quite often some early pops that are outliers, and come before the coffee has really reached first crack temperature. I would say coffee is truly in first crack when a regular sound of successive pops is heard. (If a roast is stopped right when the initial sound of first crack is heard, even accounting for some forward “momentum” from the heat stored in the coffee, it will likely taste very grainy and possibly astringent).

If I read “roast coffee through first crack,” does that mean until the very last pop is heard?

My opinion here is also no. Besides semantics, it is also hard to sense when the last sound of first crack has occurred anyway. But there are coffees that, if you are targeting a lighter roast level like City roast, you might be shutting down the heat while you are still hearing the later part of first crack? Why? Because in some cases the roast has some “momentum” in terms of heat, and will coast through the end of first crack. There is also no set understanding about coffee needing to “finish” first crack, or even what that means. Remember, roasting is a process of physical and chemical changes brought on by heat. The crack sounds are related to those changes but don’t signify anything in themselves, except one of the better clues we have to help us anticipate roast flavors.

What does it mean if first crack is rapid?

If you notice first crack sounds rapid, more than usual, their is likely too much heat being applied. A very rapid, violent first crack is, in my opinion, not the best way to roast coffee for quality taste. When you sense first crack is nearing, it’s good to bring down the temperature slightly, if you have heat control), so you enter first crack in a more controlled manner. On our larger roaster, where we usually have first crack at 400-405 f, we often moderate temperature a but at 380 f. , but we are careful not to lower the heat too much or the roast could stall.

What does it mean when there is little or no pause between 1st crack and 2nd crack?

Drum roasts usually have a pause: Air roasts that are rapid can blur first and second crack together in some cases. Really, it can happen with any roast where there is too much heat input and the Rate of Rise (ROR) in bean temperature goes out of control. Coffee changes from being endothermic (taking in heat during first part of the roast …from green to first crack), then switches to being exothermic at first crack, releasing more heat than it absorbs from the environment. That’s why a roast can change rapidly at the end and the ROR is too rapid.

What if my roast stalls during first crack?

In anticipation of first crack you might want to lower the heat so the coffee doesn’t enter first crack in a rapid and uncontrolled way. That’s a good idea generally! But if you drop your heat too much your roast might stall out. In other words the thermal “rate of rise” might flatline or even drop. There might not be enough “thermal momentum” to advance the roast and, once too much energy is lost, it’s hard to get it back. This can result in a long roast, a wonky roast curve, and perhaps a “baked” roast taste. With experience you will learn not to do this, but it can take a few lost batches to learn that.

Should first crack be completely finished before I stop my roast?

If you are aiming for a light roast, generally you do not need to wait until the absolute end of the audible first crack in order to stop the roast. Actually, the answer here is specific to the type of roaster you are using, the coffee batch and the style of roast you are going for.

I like really light roasts, so what is the soonest I can stop the roast process?

Coffee needs to enter first crack or it will have no sweetness in the cup, or a very “grainy” tasting and dry form of sweetness. But depending on the roast process and batch size, you can actually stop the roast cycle while there is still audible cracks occurring. Some say these roasts “finish first crack in the cooling tray” as one Nordic roaster put it. Ultimately, you are roasting to suit your taste. In that light, there is not a “right roast”… there’s just what’s right for you.

How do I get to a Full City roast in relation to the 1st and 2nd crack?

Full City, a roast level on the dark side of “medium roast” means the coffee has gone completely through first crack, and is in some form at the threshold of second crack. On my roaster I usually hear the first snap of second crack at 445 to 448 fahrenheit. For me, Full City is usually around 440 fahrenheit or so. For others Full City might mean they hear that first sound of second crack and then drop the roast into the cooling tray (on a commercial shop roaster). Full City is supposed to mean the full development of roast taste without the burnt notes of a French Roast. So for me that is in the range of 440 to 445 or so. Of course, these temperature measurements and the degree to which a roast continues to progress when the heat source is cut off depends greatly on the type of roaster.

What do you mean by City roast and City+ and what are they in terms of the First Crack?

City roast is a light roast level, and City + is (as you might think) “City roast with a tad more development. On my roaster I start first crack at 405 fahrenheit and it tends to come to an end with most coffees at around 418 f. In this range City roast is what I feel I get at 415 to 420, and City + usually correlates to a peak temperature of 425 to 435 or so.

How do I adjust the roaster temperature to have the best roast curve going into First Crack?

Most coffees on my roaster hit first crack at 404 fahrenheit … sometimes a bit earlier at 400 though. If I feel the roast is progressing at a good clip, with a solid Rate of Rise in temperature and roast reaction rate, I will tend to drop my burner temperature at 380 fahrenheit, 20 degrees shy of first crack. I make sure not to overreact though, as I don’t want the coffee to stall as it goes exothermic in first crack.

I heard that I should roast coffee until the surface color looks smooth and even brown. When does this happen?

Just like some people used to say ” I like coffee when the bean is dark and oily”, others believed a good roast had to do with a smooth surface appearance. Indeed there is a point where the coffee expands enough and the browning reactions have sufficiently completed that the surface no longer seems mottled in color and texture. People used to feel this correlated to a Full City roast. The issue is that different coffees will expand and brown differently, and roasting any coffee until it looks a certain way ignores the fact that how the coffee tastes is the most important thing. Nobody drinks a bitter cup of coffee and says, “I don’t enjoy this terrible brew, but in fact I know it’s good because the beans looked so smooth.”

What is Third Crack?

The quasi mythic third crack supposedly occurs after a harrowing period of silence after second crack ends. Third crack is followed immediately my spontaneous ignition and a call to 911.

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