There are two types of coffee roasting machines:
With Rotating Drum
This type is based on an operating principle:
• Conduction by heat transfer
• Roasting by direct contact from the walls of the drums, heated by the flame with the flow of hot air.
• The baking time varies between 8 to 17 minutes.
Fluid
This type is based on an operating principle:
• Heat transfer
• Hot air flow, allowing even more similar roasting temperature regulation and precise timing.
• Roasting time varies between 8 to 17 minutes.
Baking analysis
The heat used in roasting, causes the coffee beans to undergo changes such as:
• Reduction of moisture (from 12 – 8% to 5 – 1%)
• Reduction in weight (by 15 – 20% due to evaporation of water)
• Increase in volume (by 30 – 60% due to the formation of carbon dioxide)
• Change in colour (the grains become darker) change in content (+ 12 – 16 % fats, -10 % sugars, – 3 % acids)
• Development of aromas
These changes are gradual and are determined by an increase in the roasting temperature.
• 50 °C: the internal modification of the tissues begins
• 60 °C: the evaporation process begins
• 100 °C: the first colour changes occur
• Between 150 and 180 °C: light roasting stage
• Between 200 and 230 °C: optimum degree of roasting
• Between 215 and 220 °C: light roasting (more acidic and less bitter)
• Between 220 and 225 °C: medium roasting stage
• Between 225 and 230 °C: dark roasting (more bitter and less acidic)
Cooling
Cooling methods
After roasting, the coffee beans are rapidly cooled to ensure internal condensation of the aromatic substances.
There are two cooling methods:
Air cooling
• Cold air flow, rapid cooling.
• Loses some of the flavours.
• Produces fumes and scents.
Water cooling
• Fine spray in precise quantities.
• Reduction of some aromas by opening the pores of the coffee fruit.