Part 2: What Happens During the Coffee Roast Process

Let’s look at what coffee roasting is, and should be.

What happens during the ideal roast

First of all coffee is a seed, of the arabica or robusta tree. It generally has between 9-14% water inside of it. Yes, the same kind of water in our pots in the 4 experiments. When we roast the coffee, at a certain point, that water reaches the boiling point and begins to escape the bean with an audible low-volume “POP”. This commonly sounds the same as popcorn in the microwave popping, just lower volume. This is commonly what people refer to as 1st crack. It’s generally one of two indicators of the status of our roast. As the water boils away from the bean, and as we keep heating it, the bean begins to caramelize and the structure of the bean begins to expand, and stretch as the internal sugars begin to caramelize. This builds up stress in the bean to at which point the bean’s shell fractures and cracks.

Arabica coffee

This cracking can be heard and is commonly referred to as 2nd crack.  This second crack ideally happens 1-3 minutes after 1st crack.  2nd crack will sound like a tiny twig snapping, or often described as the same sound as the “snap, crackle and pop” sound that comes from the famed Rice Krispies cereal.  You can hear it if you put your ear down to it.  2nd crack sounds about like this, just louder.  You want to begin to notice this higher change in pitch, “snap” of 2nd crack vs the “pop” of 1st crack.  You can miss the difference if you’re not paying attention, or if you’ve not yet enough experience to tell the difference.

This second crack should be your indicator of when to stop the roast if you’re a beginner and, for the most part any roaster generally should not exceed 1 minute past 2nd crack, pretty much ever.  Fire comes next.

I recommend that you pull your coffee for cooling at a place I have coined “10-in-10” That’s 10 cracks within a 10 second window. This should be your marker for the official 2nd crack start, where most beans are just starting to undergo 2nd crack. Some beans have the tendency to fire early, and this is a poor indicator of the arrival of second crack.

So once we have determined the amount of heat needed to cause 1st crack and 2nd crack to arrive at just the right time, then we can roast back to back, day after day, using that same volume and same temperature to repeatedly roast over and over with an absolute degree of accuracy, even to the point of being able to predict 1st and 2nd crack to within 15 seconds. Much like boiling the same 1 cup of water at a setting of five on the stove would cause the water to boil at exactly the same time every time. This is our end goal.

Results of Too Much Heat:

If you were to inject heat into the roast too quickly, much like boiling water faster, the roast would happen on a much faster time scale.  So instead of the above ideal scenario where the roast approaches first crack nicely then 1st crack subsides, with a 1-3 minute gap between 1st and 2nd, then 2nd crack begins, you can accelerate the roast so quickly that it goes into 1st and 2nd all within the same cracking sequence.  In other words it happens so quickly, it blends 1st and 2nd crack together into one mass crack.  This is always an indicator of TOO MUCH HEAT.  

Under this scenario you will get no gap between the cracks and the untrained ear will assume that mass-crack is only 1st crack and second crack is still minutes away (you can hear a difference in the two). In reality 2nd crack is done when the cracks stop and you are minutes away from a fire. The key thing here is to recognize that you have too much heat and you must slow things down by reducing heat. The goal is to find the relative temperature at which your grill can perform (see the article on thermometer relativity) the roast to the ideal conditions as above. That will require generally 1-4 roasts to figure out what your roaster is doing. After you have 1 pound figured out to the ideal temperature for your grill, then you can add 25-40 degrees of temperature for every 25% more volume you add to your drum.

Results of too little heat:

Conversely, having too little heat during your roast will cause things to drag out, really long. The first indicator that your roast is running long, and that you are falling behind the time curve, is the steam that normally appears about 1 minute prior to 1st crack. If about 1 minute prior to the target 1st crack time, you have no apparent steam, then it tells you that you don’t have enough heat as things are falling behind your time curve. At this point you need to accelerate the roast process and add approximately 25 degrees of heat (or more if you’ve been roasting at a very low temperature) and get your roast back on your desired time curve.

Leaving the temperature too low will cause the roast to drag out to an eventual 1st crack, then you’ll have a long 3-7 minute window between 1st and 2nd and then finally 2nd will start. The cracking times will be much longer in this case, much like boiling the water on setting 2 (Low/Simmer) will just take forever. The bad thing about this, is that your roast time will be lengthened and your coffee will taste increasingly bla, bland and boring. Never take your chosen volume of coffee, beyond it’s prescribed roast time or your coffee will get increasingly bland and baked.

What if i mess up?:

A minute or two late on 1st or 2nd crack isn’t going to make much discernable difference to anyone but the cupping elite, and especially to your average coffee drinker; incidently, should your roast be late, it doesn’t mean that you’ve ruined it. It might only mean it’s not as good as it could be. Strive to keep your roasts on time, and you’ll come out with excellence every time.

fine-tuning your roast

There is always room for improvement beyond this blanket, standard profile. Choosing an ideal starting temperature, then adjusting the temperature up or down during the roast, depending on what coffee origin you choose, finishing the roast darker or lighter to accent the flavor characteristics of your origin bean are always ways to improve your roasts. Researching your particular bean at Sweet Marias, then fine-tuning your roast profile and roast level to that bean are ways to improve it even more.

These fine-tuning subjects are beyond the scope of these articles as our goal is to give you a starting point, and a “no-fail” blanket solution that will work across the board on any coffee you happen to choose, to the approval of quite likely everyone you know.   

Personally, I have found that I can roast just about any coffee, of any quality, to this standard level, and most customers beat down my door to get at more. When your coffee is this fresh you just can’t lose compared to other locally available coffee. But remember, if you don’t deliver fresh-roasted coffee (Within 2-3 weeks max) and preferably within 48 hours of the roast, your coffee will increasingly become as stale as everything at the supermarket. Your main business advantage is freshness. And people can taste it once they have tried it and try to return to their old coffee.


You must find the ideal temperature for your grill for the given mass of coffee that you are doing, where the coffee finishes on time for each drum with a given mass, these charts. Temperature is just a suggestion. You need to discover what works for YOUR grill.

Free Roasting School For New Drum Customers!

If you’re having trouble with this process, we offer free roasting school and simultaneous teaching while you roast if you would like some help.