Coffee Industrial Process_Paola Muggia_V1 -Coffee Roasting Process & Equipment

Coffee Supply Chain Overview

  • Flow: Purchase green beans → transport → warehouse storage (controlled temperature & humidity) → cleaning → optional pre-blending → roasting → grinding → packaging.
  • Proper storage of green beans preserves quality prior to production.

Cleaning (Pre-Roasting)

  • Removes contaminants by:
    • Density separation.
    • Size separation.
    • Ferromagnetic removal of metal.
    • Elimination of wood, stones, other foreign matter.
  • Critical: prevents equipment damage & keeps raw-material quality high.

Blending

  • Purpose
    • Compensates for origin & crop variability; ensures flavor consistency.
    • Becomes a brand’s “fingerprint.”
  • Two strategies
    1. Pre-blend (raw blend)
    • Mix different green origins, then roast the single mixed batch.
    • Advantages: easier mechanical handling (beans still hard); simpler process flow.
    • Requirement: ingredients must match in size, moisture, overall quality to roast homogeneously.
    1. Post-blend (split roast)
    • Roast each origin separately, then blend roasted fractions.
    • Advantages: can roast each component to its optimal degree; allows multi-degree blending for complex profiles.
    • Drawback: roasted beans are fragile → gentler, costlier handling.

Roasting Fundamentals

  • Definition: Application of heat to transform green coffee into roasted coffee.
  • Key success factors
    • Generate correct temperature at the right moment.
    • Monitor & stop precisely to avoid over- or under-roast.
  • Heat transfer modes
    • Conduction: direct bean–hot‐surface contact; risk of scorching; minimal control.
    • Convection (preferred): hot air envelopes beans; gives uniform, controllable heating.
    • Radiation: minor, hard to control.

Time–Temperature (Roast Curve)

  • X-axis: time; Y-axis: batch temperature.
  • Operators modulate both slope and end-point.
  • Typical segments on the curve:
    • Optional pre-heating (< 100^{\circ}C): uses exhaust air; saves energy, stabilizes roast entry.
    • Phase 1 – Drying:
    • Beans enter chamber (~200\text{-}300^{\circ}C environment).
    • Water (~10\% w/w) evaporates → internal vapor pressure builds.
    • Ends at “First Crack” (audible pop, ≈ 190^{\circ}C for many coffees).
    • Phase 2 – Roasting (Maillard & pyrolysis):
    • Color shifts from yellow → brown.
    • Complex chemistry forms flavor precursors & volatile aroma.
    • Phase 3 – Cooling / Quench:
    • Immediate heat removal (water mist + air or air-only).
    • Targets exit-bean temp ≈ 30^{\circ}C.
    • Excessive quench water ↑ final moisture → accelerates oxidation & shortens shelf life.

First & Second Crack

  • First Crack (light roast threshold): sharp, popcorn-like; marks escape of steam, structural expansion.
  • Second Crack (dark roast zone): softer, harder to hear; further cell wall fracture, oil migration, very dark surface.

Sensory Impact of Degree of Roast

  • Roast flavor intensity ↑ with darker roasts.
  • Acidity: high in light, decreases in dark.
  • Bitterness: low in light, ↑ in dark.
  • Aroma descriptors
    • Light: fruity, floral.
    • Medium: caramel, sweet.
    • Dark: chocolatey, smoky/roasty.
  • Body/mouthfeel: light roast → thinner; medium/dark → fuller.

Modulating the Roast

  • End-point temperature & time define “degree of roast.”
  • Multiple stop points on same curve produce light, medium, dark outputs.
  • Trial-and-error cupping couples sensory data with curve tweaks.

Roast Time Regimes

  1. LTLT – Low Temperature / Long Time
    • 9\text{–}20 min.
    • Creates homogeneous internal roast, moderate bulk-density loss.
  2. Fast Roast
    • 1\text{–}6 min (enabled by high-air-flow systems).
    • Beans heat & pop quickly → higher expansion, lower bulk density, higher extraction yield (ideal for instant coffee).
    • Larger thermal gradient surface ↔ core → interior may be lighter than shell.

Curve Shape Variations

  • Conventional: steep initial slope (aggressive drying) then gentle slope (controlled development).
  • Non-traditional: slow start or bespoke ramps; explored via experimentation.

Cooling Strategies & Quality

  • Water quench + air: fastest but risks high final moisture.
  • Air-cool only: preferred for specialty quality; preserves volatiles, extends shelf life.

Roasting Equipment

1. Drum Roaster (Rotating Drum)

  • Horizontal perforated drum; batch mode.
  • Heat split: ~70\% convection (hot gases through perforations) + 30\% conduction (wall contact).
  • Internal helical flights lift → drop beans for mixing.
  • Critical settings: optimal batch load, drum RPM (too fast = centrifugal sticking, too slow = poor mixing).
  • Typical roast range: 8\text{–}20 min (LTLT).
  • Plant layout: burner → hot air → drum → cyclone (chaff removal) → cooling tray → stoner → grinder.

2. Fluidized Bed Roaster

  • Invented ~1970s; fixed column with perforated plate.
  • Large hot-air flow suspends ("fluidizes") beans; nearly 100\% convection.
  • Enables super-fast roasting: 1.5\text{–}8 min.
  • Load/airflow ratio must be tuned throughout roast (bean density drops). Problems:
    • Under-load → chaotic flight, uneven roast.
    • Over-load → insufficient lift, bottom over-roasts.
  • Dual use for roasting & rapid air cooling; two batch chambers can run in staggered cycles for quasi-continuous operation.
  • Long roasts (> 10 min) strip volatiles due to high air throughput.

3. Tangential Roaster

  • Hybrid: fixed drum + rotating paddles + airflow.
  • Broad flexibility (short or long roasts) by adjusting paddle speed, gas temp, airflow.

4. Centrifugal Roaster

  • Horizontal rotating bowl; centrifugal forces move beans to rim then they fall back through centre.
  • Convection dominant during free-fall; conduction minor.
  • Roast times: 3\text{–}12 min.

Post-Roast Stone Removal

  • "Stoner" unit uses density difference after roast to eject stones that cleaning missed; protects grinder burrs.

Practical Advice to Aspiring Roasters

  • Roasting = science + art; only mastering through practice & sensory evaluation.
  • Continually adjust variables (temperature, time, airflow, load) & cup results.
  • Combine analytical tools (color, weight loss) with tasting notes for process control.

Ethical / Practical Implications Mentioned

  • Energy saving via pre-heating & air recirculation.
  • Environmental compliance: cyclones & scrubbers to clean exhaust.
  • Water-quench trade-off: faster processing vs product shelf life & quality.

Key Numerical References (all in LaTeX)

  • Water in green beans: \approx10\%.
  • Roasting environment: 200\text{–}300^{\circ}C.
  • First crack onset: \sim190^{\circ}C (bean internal temp).
  • Light → dark roast curve span often \sim180^{\circ}C → 230^{\circ}C depending on profile.
  • Cooling target: \le30^{\circ}C bean temperature.
  • LTLT duration: 9\text{–}20\,\text{min}; Fast roast: 1\text{–}6\,\text{min}.