In brief
Second crack is the second burst of crackling a roaster hears, late in the roast. It comes well after first crack. Wikipedia places it at a bean temperature of about 224 °C (435 °F).
The sound means the bean's structure has turned brittle and is fracturing. Oils that were locked inside start moving to the surface. That is why beans roasted into second crack look glossy.
For a home brewer, second crack is the line into dark roast. Coffee taken past it tastes more of the roast than of where it was grown, and it grinds and brews differently.
On this page · 5 sections
What causes second crack?
Second crack happens when gas pressure inside an already brittle bean fractures its structure. MTPak cites Scott Rao's The Coffee Roaster's Companion: "the accumulation of CO2 is the main driver of second crack."
Wikipedia describes the same moment from the bean's side. The structure becomes "brittle and fracturing as the bean continues to swell." Heat and pressure also liquefy lipids inside the bean, which can often be seen on the surface.
Second crack comes well after first crack. MTPak gives its temperature as about 224 °C, the same figure Wikipedia uses.
What roast levels come after second crack?
The traditional dark roast names all sit around or beyond second crack. Wikipedia lists approximate bean temperatures for each.
| Roast name | Temperature | Look |
|---|---|---|
| Full City | 225 °C (437 °F) | Medium-dark, faint oil patches |
| Vienna | 230 °C (446 °F) | Moderate dark brown, light surface oil |
| French | 240 °C (464 °F) | Dark brown, shiny with oil |
| Italian | 245 °C (473 °F) | Nearly black and shiny |
Treat the temperatures as approximate, not exact cutoffs. Flair Espresso uses a simple rule: dark roast means beans that have "at least hit the second crack."
What does second crack do to flavor?
It shifts the cup from origin flavor toward roast flavor. Wikipedia says that beyond second crack, coffee turns "full-bodied and bittersweet" and "little origin character remains."
A short way into second crack can still be pleasant. MTPak quotes Kenneth Davids describing a cup that is "pungent, yet sweet and full-bodied with a roasty flavour," without acidity. Roast further and MTPak says it tastes "burnt and smoky," and eventually "like charcoal."
Do second-crack roasts need a coarser grind?
Usually, yes. Counter Culture explains that a darker roast's cellular structure is more degraded, making it less dense, so darker roasts need coarser grinding than lighter ones.
Flair Espresso makes the same point for espresso. Dark roasts "give up their soluble material a lot more easily," so it suggests grinding a little coarser. It also suggests lower brew temperatures, starting as low as 85 °C for very dark roasts.
In practice, take your usual setting for the method and open it up a little. Then adjust by taste, as covered in dialing in. If a recipe was written for another grinder, the grind converter gives you the matching starting point on yours.
Are oily, dark beans bad for your grinder?
They are harder on it, mainly through buildup. Baratza says dark roasts "need cleaning more often due to the oils they leave in the grinder." It adds that "coffee sticks to the oil," which raises the risk of clogs.
Baratza's routine cleaning interval is every 4 to 6 weeks. If you grind mostly dark roast, it highly recommends grinder cleaning tablets to absorb oils. Grinding only the dose you need, known as single dosing, keeps beans out of the hopper between brews.
If you are buying a grinder mainly for dark roasts, ease of cleaning is worth weighing. You can compare models on the grinders page.
Sources
- Wikipedia: Coffee roasting
- MTPak: A guide to first and second crack
- Flair Espresso: Espresso University, demystifying dark roasts
- Counter Culture Coffee: Coffee basics, grind size
- Baratza: Grinder cleaning essentials
By Jeff Gluck · Checked Oct 21, 2026