Probat UG 22, Sensory Lab Roastery
Coffee Roasting
"Coffee roasting is a chemical process by which aromatics, acids, and other flavor components are either created, balanced, or altered in a way that should augment the flavor, acidity, aftertaste and body of the coffee as desired by the roaster."
Coffee roasting is the procedure that creates a consumable product from raw organic matter. Through out the roast process raw coffee goes through numerous physiological and chemical changes as the temperature within, and surrounding the beans increases. Each change and its timing within the roasting process has a varied affect on the coffee’s flavour profile. It is only through the control of this process that we get the full spectrum of flavours associated with specialty coffee.
Basics.
At a purely fundamental level, roasting is the process of controlled heat transfer to raw coffee beans. The operator uses controls such as airflow, gas levels, drum speed, and charge weight (amongst others), influencing the heat progression to reflect his desired profile. It can be as short as eight minutes or as long as 30, each producing radically different end results. The coffee ‘charge’ is dropped into the drum at a temperature designated by the operator (usually between 160C and 200C). A varied approach can be taken from here that will inevitably lead to “First Crack”. First Crack primarily refers the audible sound of gas being expelled from the coffee beans as the cell fibres break. From this point on the coffee is at a point that it can be removed from the roaster with the operator deeming when the coffee is ‘done’. The coffee must then be cooled in a very short space of time to prevent any further changes.
Roast Profiles
To achieve a desired outcome from the roast process and maintain consistency, most roasters will implement roast profiles. A roast profile simply is a list of steps or adjustments and when to execute them. This can pertain to any of the previously mentioned controls, a temperature reference, and/or a time point. While these adjustments can be simple, pertaining to only one control and one reference point, the better profiles will contain multiple references; i.e. at 8mins and 160C reduce flame to 60%. By providing more information the operator will have a greater understanding of what is required to produce the correct outcome.
Example Profile.
Coffee: Guatemala San Antonio
Charge: 18kg
Drop Temp: 170
Steps:
120C @ 0:08 (Fully charged drum)
145C @ 2:00 (Air Temp 114C 2 burners)
205C @ 3:00 (Air Temp 138C 3 burners)
200C @ 6:30 (Bean colour straw, air 180)
195C @ 9:30 (Air Temp 196C, 1 burner)
First Crack @ 10:55-11:15 (Bean temp 169C)
200C @ 12:00 (Bean temp 174C Air Temp 193C)
205C @ 13:00 (Bean temp 179C Air temp 199C)
Roast Finish @ 14:00-14:30 (Bean Temp 185C)
Primary changes during the roast
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-Drying:
Moisture content of raw coffee is between 9-12% when it gets to the roastery. As the coffee absorbs heat majority of the remaining moisture evaporates from the beans (or changing chemically to contribute to later reactions). During this they turn from varying shades of green, to jade, then to a straw yellow.
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-Primary Development: From a straw colour the coffee darkens to a medium brown*
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-First Crack: This Audible stage happens when gas, trapped in the coffee’s cells, reaches a critical pressure and splits the cell walls. At this point the heat in the roaster changes from exothermic (external source) to endothermic (internal source).
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-Secondary Development: From the end of first crack you have another stage that contributes ‘roast flavour’; those of browning sugars, cocoa & heavy earthy notes. The length of this development time will determine how present these flavours are in the coffee at the end.
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-Second Crack: Similar to First Crack this is a second expulsion of gas from built up pressure with in cell structures.
-
-Drying:
Moisture content of raw coffee is between 9-12% when it gets to the roastery. As the coffee absorbs heat majority of the remaining moisture evaporates from the beans (or changing chemically to contribute to later reactions). During this they turn from varying shades of green, to jade, then to a straw yellow.
-Primary Development: From a straw colour the coffee darkens to a medium brown*
-First Crack: This Audible stage happens when gas, trapped in the coffee’s cells, reaches a critical pressure and splits the cell walls. At this point the heat in the roaster changes from exothermic (external source) to endothermic (internal source).
-Secondary Development: From the end of first crack you have another stage that contributes ‘roast flavour’; those of browning sugars, cocoa & heavy earthy notes. The length of this development time will determine how present these flavours are in the coffee at the end.
-Second Crack: Similar to First Crack this is a second expulsion of gas from built up pressure with in cell structures.
