Doneness & Temps

Beverage Temperatures

Coffee Roast Stages: First & Second Crack

Also: first crack coffee, second crack coffee, coffee roasting cracks, light roast first crack, dark roast second crack, development phase

Two audible cracking events during roasting that mark the entry into light roast (first crack, ~196–204°C) and dark roast (second crack, ~224–230°C), with flavour development occurring in the window between them.

Coffee roasting progresses through a series of physical and chemical transformations that culminate in two audible cracking events. First crack (196–204°C / 385–400°F) is caused by the steam and CO₂ pressure inside the bean exceeding cell-wall tensile strength — the bean physically expands and the outer chaff skin fractures, producing a rapid popcorn-like cracking sound. This marks the entry to drinkable (light) roast. Second crack (224–230°C / 435–446°F) is caused by the brittle, now-caramelised cellular structure fracturing under thermal stress, producing a quieter, more rapid crackling. This marks the entry to dark roast. Development time — the minutes between first crack onset and the end of the roast — is the master variable for flavour profile.

In photos

Coffee Roast Stages: First & Second Crack at First crack: 196–204°C (385–400°F); Development phase: 204–224°C (400–435°F); Second crack: 224–230°C (435–446°F). During first crack, endothermic bean drying gives way to exothermic pyrolysis. Visual cues: First crack: distinct rapid popping sounds resembling popcorn, one pop at a time; bean colour shifts from yellow to light tan/cinnamon, Development phase: sound quietens; bean colour develops from cinnamon through medium brown; sweetness and roast aroma become detectable, City roast (just after first crack): light brown, matt surface, no surface oils; bright acidity, floral/fruit notes.
Coffee Roast Stages: First & Second Crack at First crack: 196–204°C (385–400°F); Development phase: 204–224°C (400–435°F); Second crack: 224–230°C (435–446°F). During first crack, endothermic bean drying gives way to exothermic pyrolysis. Visual cues: First crack: distinct rapid popping sounds resembling popcorn, one pop at a time; bean colour shifts from yellow to light tan/cinnamon, Development phase: sound quietens; bean colour develops from cinnamon through medium brown; sweetness and roast aroma become detectable, City roast (just after first crack): light brown, matt surface, no surface oils; bright acidity, floral/fruit notes.
Coffee Roast Stages: First & Second Crack in context — the stages just below and above, side-by-side. Coffee roasting progresses through a series of physical and chemical transformations that culminate in two audible cracking events. Target reference First crack: 196–204°C (385–400°F); Development phase: 204–224°C (400–435°F); Second crack: 224–230°C (435–446°F).
Coffee Roast Stages: First & Second Crack in context — the stages just below and above, side-by-side. Coffee roasting progresses through a series of physical and chemical transformations that culminate in two audible cracking events. Target reference First crack: 196–204°C (385–400°F); Development phase: 204–224°C (400–435°F); Second crack: 224–230°C (435–446°F).
Coffee Roast Stages: First & Second Crack in practice — Specialty single-origin filter roasts (dropped at light roast, just after first crack). Like meat, a roasting bean carries significant thermal inertia.
Coffee Roast Stages: First & Second Crack in practice — Specialty single-origin filter roasts (dropped at light roast, just after first crack). Like meat, a roasting bean carries significant thermal inertia.

What happens

During first crack, endothermic bean drying gives way to exothermic pyrolysis. Sucrose undergoes caramelisation; Maillard reactions between amino acids and reducing sugars generate hundreds of aromatic compounds (pyrazines, furans, ketones). Cell walls rupture, releasing CO₂. The bean roughly doubles in volume as density falls. Between the cracks, organic acids degrade progressively (chlorogenic acids break down, reducing perceived acidity), body develops, and roast character deepens. At second crack, oils migrate to the surface, the cellular matrix carbonises, and bitter compounds (pyridines, quinolines) increase. Beyond second crack, the roast rapidly approaches burning and the cup profile collapses to a uniformly dark, charred character.

What to look for

  • First crack: distinct rapid popping sounds resembling popcorn, one pop at a time; bean colour shifts from yellow to light tan/cinnamon
  • Development phase: sound quietens; bean colour develops from cinnamon through medium brown; sweetness and roast aroma become detectable
  • City roast (just after first crack): light brown, matt surface, no surface oils; bright acidity, floral/fruit notes
  • Full City roast (first crack fully settled): medium-brown, still dry surface; balanced acidity and body
  • Second crack onset: rapid, finer crackling sound, somewhat like crinkling cellophane; colour is dark brown, oils beginning to emerge
  • French/Italian roast (into/beyond second crack): very dark, glossy oily surface; bittersweet, smoky, low acidity

How to check

  • Listen carefully during the roast — first crack is unmistakably loud and rhythmic; second crack is quieter and more rapid
  • Use a drum roaster with a bean-probe thermometer to log temperature; first crack onset is audible but probe temperature confirms it
  • Sample beans via a trier (roaster sampling spoon) during development to assess colour with a colour tile or Agtron meter
  • For home drum roasters, a cooking thermometer in the roasting chamber correlates approximately to these crack temperatures, though bean-probe temps are more accurate
  • Timing development: from first crack onset to drop, 20–25% development time ratio (DTR) is a common specialty target

The science behind it

  • Maillard reaction

    Non-enzymatic browning between amino acids and reducing sugars; responsible for roasty, complex flavour development between the cracks

  • Caramelisation

    Sucrose pyrolysis beginning around 170°C; contributes sweetness and body, precedes first crack

  • Development time ratio (DTR)

    Percentage of total roast time spent after first crack; 20–25% DTR is a specialty benchmark for balanced development

  • Agtron number

    Spectrophotometric colour measurement of ground coffee; light roast ≈ 75–85, medium ≈ 55–65, dark ≈ 35–45

  • CO₂ degassing

    Roasted beans off-gas CO₂ for days to weeks; high-CO₂ fresh-roasted beans bloom vigorously during brewing

  • Chlorogenic acid degradation

    Major coffee acid; breaks down progressively through roasting, reducing perceived sourness and bitterness from this source

Appears in

Specialty single-origin filter roasts (dropped at light roast, just after first crack)Espresso blends (typically medium to medium-dark, stopped in development phase)French press roast (medium-dark, full development phase)Italian espresso tradition (into or just past second crack)Cold brew blends (medium-dark to dark, often developed for low-acid sweetness)Moka pot coffee (traditionally dark roast, often past second crack)

References

  1. 1.The Coffee Roaster's Companion — Scott Rao
  2. 2.The World Atlas of Coffee — James Hoffmann
  3. 3.Craft Coffee: A Manual — Jessica Easto
  4. 4.Modulating the Flavor Profile of Coffee — Specialty Coffee Association Research

Confidence: high

Notes

Carryover after drop

Like meat, a roasting bean carries significant thermal inertia. If dropped into a cooling tray, the bean temperature continues to rise 2–5°C before cooling begins. Roasters targeting a specific crack stage often drop slightly before the bean-probe reading reaches the nominal temperature, relying on carryover to complete development.

Variable crack temperatures

Exact crack temperatures vary meaningfully with bean density, moisture content, and roaster design. Dense, high-altitude beans (e.g. Ethiopian Yirgacheffe) may first crack at 202–205°C; lower-density washed Centrals may crack at 196–198°C. Published ranges are indicative; a skilled roaster calibrates to their own machine and green bean lot.