Coffee · CrackLog
What is first crack in coffee roasting and how to time it
First crack is the moment roasting coffee beans audibly pop as steam and gas rupture the bean structure, usually when the bean mass reaches about 196 to 205 C (385 to 400 F). It marks the start of development. Most roasters time the roast from that point, targeting roughly 15 to 25 percent of total roast time after first crack.
What is physically happening at first crack
A green coffee bean holds water inside a dense cellular structure. As the bean heats through the drying and yellowing stages, that water turns to steam and the sugars begin to brown. Pressure builds inside the seed until the cell walls can no longer hold it. When they give way, the bean expands and makes a sharp snapping sound. Roasters call this first crack because a second, softer round of popping happens later if the roast continues.
Mill City Roasters describes the sound as the rupture of the endosperm deep inside the seed, and notes that the steam released briefly slows the roast. On a temperature graph this shows up as a short dip in the rate of rise, sometimes called the crash. The bean also swells to roughly double its original volume by this point, and the process shifts from absorbing heat to releasing it.
First crack matters because it is the most reliable sensory landmark in a roast. Temperature readings differ between roasters and probe placements, but the sound is the same whether you use a popcorn popper, a hand net over a gas flame, or a small drum. Almost every roasting method that home roasters use treats first crack as the reference point for the rest of the roast.
What temperature and time to expect
Bean temperature at first crack is commonly reported between 196 and 205 C, which is 385 to 400 F. Mill City Roasters puts the typical figure around 390 F, and Dabov Specialty Coffee gives the 196 to 205 C range. The exact number depends on the bean density, batch size, moisture content and where your thermometer sits, so treat your own roaster's reading as the number to remember rather than a universal constant.
In time, first crack usually arrives around 9 to 12 minutes into a drum roast according to Dabov, and the cracking itself continues for roughly 30 to 60 seconds as individual beans reach pressure at slightly different moments. Air roasters and popcorn poppers move heat into the beans much faster and reach first crack sooner, so do not be surprised if your machine is well outside the drum roaster figures.
Second crack starts later, typically around 420 F (about 215 C) according to Mill City Roasters. It sounds softer and more like a crackle than a pop, and it is accompanied by more smoke and oil on the bean surface. Most specialty roasters stop before or just at the start of second crack, and Mill 47 notes that stopping at the beginning of second crack produces what is often called a full city roast.
How to hear first crack reliably
The sound is easiest to identify in a quiet room. Fans on air roasters and popcorn poppers are loud, so many home roasters lean in close or hold the roaster near their ear at the point they expect the crack. On a drum roaster the first pops carry through the drum wall clearly.
Do not mark the very first isolated pop. Mill City Roasters recommends waiting for three to five pops in rapid succession, which they call rolling first crack, before treating first crack as started. A single early pop is often one small or damaged bean and will throw your timing off if you log it as the start.
Watch for the supporting signs. Just before first crack the beans shift from yellow to light brown, the smell changes from grassy or bread like to something closer to toast, and a little smoke may appear. If you see those changes but hear nothing, keep listening rather than adding heat, because rushing the approach makes the crack arrive harder and less evenly.
Timing development after first crack
Development time is the stretch between first crack and the moment you drop the beans out of the roaster. Development time ratio, usually written DTR, is that stretch divided by total roast time, expressed as a percentage. If first crack starts at 9 minutes and you drop at 11 minutes, development is 2 minutes and DTR is 2 divided by 11, or about 18 percent.
Scott Rao, whose books popularised the measure, recommends 20 to 25 percent for most roasts on classic drum roasters running above 60 percent of capacity. He reports that of more than 20,000 roasts he had tasted, 18 of the best 20 fell in that band. He also notes exceptions, including sample roasters and machines with a lot of burner power relative to batch size, where a DTR around 15 percent can still taste fully developed.
Dabov gives a broader working range of 15 to 25 percent overall, with about 10 to 15 percent for light roasts, 18 to 22 percent for medium and 22 to 28 percent for medium dark, and warns that going past about 30 percent tends to produce a flat, bitter cup. Mill 47 mentions the older habit of adding a fixed 3 to 4 minutes after first crack instead of a percentage. Both approaches work as long as you use the same one every time and change only one variable per roast.
A practical way to hit a target is to decide the DTR before you start, then compute the drop time the moment first crack begins. For a 10 minute first crack and a 20 percent target, total time should be 12.5 minutes, so the drop is 2.5 minutes after the crack. Logging the crack to the second makes this arithmetic simple. CrackLog, for example, places a marker on the curve at the exact second you tap when you hear the crack and shows the ratio as the roast continues, so the drop decision is a number rather than a guess.
Common first crack mistakes and how to fix them
Stalling before the crack. If the temperature rise flattens out in the minute before first crack, the crack can be weak and drawn out, and the coffee often tastes baked or papery. Keep a steady, gentle rise into the crack rather than cutting heat early.
Charging too hot. Too much heat early drives the outside of the bean ahead of the inside, so first crack sounds violent and arrives before the interior has browned. Expect a longer, quieter first crack when the approach is gradual.
Confusing the crash with a problem. The short slowdown in temperature rise at first crack is normal and is caused by the steam leaving the beans. Adding a lot of heat to fight it can push the roast into a fast flick afterwards. Small adjustments are enough.
Not writing anything down. Most timing problems come from having no record. Note bean weight before and after, charge temperature, time and temperature at first crack, drop time and the resulting weight loss. Comparing weight loss across batches tells you whether your development is consistent even when the sound was hard to hear.
Frequently asked questions
Does every coffee crack at the same temperature
No. Dense, high grown beans tend to crack later and at slightly higher readings than soft, low grown beans, and decaf often cracks quietly and early. The 196 to 205 C range is a guide, not a rule, so record what your own roaster shows.
Can I stop the roast at first crack
You can, but coffee dropped at the very start of first crack often tastes grassy or sour because the interior has not developed. Most roasters give the beans some development after the crack begins, and the 10 to 15 percent DTR that Dabov lists for light roasts is a reasonable minimum.
What is the difference between first crack and second crack
First crack is a loud pop caused by steam and gas rupturing the bean, around 196 to 205 C. Second crack is a softer crackle around 215 C caused by the cell structure breaking down further, with visible oil and more smoke. Second crack means a dark roast.
Why does my air popper reach first crack so quickly
Hot air transfers heat to the beans much faster than a drum, and batches are tiny, so first crack arrives well before the 9 to 12 minutes typical of drum roasters. Because total time is short, a 20 percent DTR is only a small number of seconds, so time it with a stopwatch rather than by feel.
Do I need a thermometer to time first crack
No. The sound is the marker. A thermometer helps you repeat a roast, but a timer and a written log of when the crack started and when you dropped the beans are enough to control development time.
