Coffee Bean Roasting of Select Gourmet Coffee:
History and Mystery
The History of Coffee Roasting
The true origins of roasting select gourmet coffee are lost to history:
1) Coffee was first consumed raw – fruit and seeds were dried and eaten
2) Arabs “discovered” coffee being used as food supplement by indigenous people
living in what is today Ethiopia
3) It is believed that the Arabs were the first to utilize roasting, grinding,
and boiling the coffee seeds to create the beverage “coffee”
4) Islam forbids the consumption of alcohol, so coffee became their “wine” to
fulfill the human need to sit and relax in community with other people
5) Since freshly harvested coffee seeds are very moist, it is likely that
parching the coffee to preserve it resulted in the first primitive (and likely
accidental) roast
Evolution of Coffee Roasters
1800 to 1900:
Conductive Drum Roaster (Indirect Heat)
1) Flame(s) under roasting drum created from wood or coal
2) Drum is turned by hand or by horse
3) Beans are heated by contact with drum
4) No airflow through drum
5) No sampler
6) No controls – roasting by seat of pants
7) Roast time up to 50 minutes
1900 to 1930:
Radiant Drum Roaster (Direct Heat)
1) Flame(s) - from underneath through openings in perforated drum, or from
flames in the drum with the coffee – created from coal or gas
2) Drum is turned by belts or electrical motors
3) Beans are heated by contact with flame and metal of drum
4) Little airflow through drum
5) Sampler available
6) Limited controls – thermostat only
7) Roast time up to 30 minutes
1930 to Present:
Conductive & Convective Drum Roaster (Indirect Heat)
1) Flame(s) under roasting drum or in separate chamber created from coal or gas
2) Drum is turned by belts or electrical motors
3) Beans are heated by contact with drum
4) Hot airflow through drum
5) Sampler available
6) Limited controls – thermostat only
7) Roast time up to 15 minutes
1960 to Present:
Convective Fluid Bed Roaster (Indirect Heat)
1) Flame(s) in separate chamber created from gas or electricity
2) No moving parts in roaster. Blower propels hot air through coffee
3) Beans are heated by contact with hot air from blower
4) Hot airflow through chamber tumbles beans to avoid scorching
5) No sampler available
6) Completely automatic
7) Roast time up to 15 minutes
How green coffee parameters influence roasting
Moisture and roasting
1) Evaporation of free moisture in first phase or roast (up to “first crack”)
2) Level of moisture influences speed of roasting
High moisture beans (>12%)
1) Almost ‘bloated’ / deep green color
2) Soft and 'spongy' feel
3) Wet grass smell
4) Bite test: hard to fracture
5) Often new crops, especially from Indonesia
6) Need to roast higher termperatures for longer time
Low moisture beans (<12%)
1) Faded color (light green to yellow)
2) Brittle feel
3) Dry hay smell
4) Bite test: easy to fracture
5) Often late or past crops, especially from Latin America
6) Need to roast lower temperatures for shorter times
Five primary things occur during roasting
1) The beans lose weight (about 16-20%) primarily from loss of residual water,
but also from loss of oils and other volatile materials
2) The beans expand in size; the darker the roast, the greater the expansion
3) The beans darken due to caramelization of the natural sugars
4) Soluble oils are released, and move onto the surface of the bean
5) Flavors and aromas we associate with coffee are created
Physical changes to coffee during roasting
1) Over 800 chemical reactions known – probably more that are unknown
2) Moisture and weight loss during roasting stages
3) Bean fiber carbonization
4) Plant sugar caramelization
5) Fracturing of cell wall
6) Oil migration from cells to surface of beans
7) Bulk density changes – beans get bigger yet lose weight during roasting
Measuring roast levels to ensure consistency
1) CBI utilizes an Agtron® color photometer to measure and record the roast
levels of every roast we do
2) Agtron machine and scale is the industry standard in specialty coffee
3) Roast levels are accurately measured by gauging depth of ground coffee color
4) CBI has established tight roast specs for every coffee that must be met, or
roast is rejected
5) Agtron scale is 1 – 100. Number refers to the % of light that is reflected
off the surface of the ground coffee (darker colors absorb light, lighter colors
reflect light)
6) Higher Agtron numbers are lighter roasts, lower Agtron numbers are darker
roasts
7) CBI light roast Agtron is typically about 45 (depending on the origin)
8) CBI dark roast Agtron is typically about 25 (depending on how dark)
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