Bean-to-bar manufacturing: roasting, winnowing, refining, conching and tempering
This domain tests the process logic of bean-to-bar: what each unit operation does to flavour, texture and stability, and what happens when it is pushed too far.
Roasting
Roasting, typically 110-160 degrees C for 15-45 minutes, drives off water and acetic acid, develops Maillard and Strecker chemistry (pyrazines, aldehydes, thiols) and sets the balance between fruity and roasted notes. Whole-bean roasting keeps the husk as insulation and allows a lighter roast; nib roasting is faster and more even. Gentle, longer profiles protect origin aromatics; fast, hot profiles flatten them.
Winnowing
Cooled beans are cracked and the brittle husk is separated from nibs by sieving and air classification. Nib size should be uniform: too much fine dust gives a gritty melt and carries more husk into the batch.
Refining
Roller refiners or ball mills reduce sugar and cocoa particles to below 20-25 microns, the threshold of tactile detection. Above that, chalkiness and grittiness appear even when the flavour is excellent.
Conching
Conching (45-80 degrees C, 6-72 hours, through dry, paste and liquid phases) reduces moisture, viscosity and volatile acidity, rounds off harshness and builds mouthfeel. Over-conching strips delicate fruit and floral notes; under-conching leaves a sharp, sour edge.
Tempering
Cocoa butter has six polymorphs. Form V is the target, melting at 32-34 degrees C. Temper dark chocolate by melting to 45-50 degrees C, cooling to about 27 degrees C to form stable nuclei, then reheating to 31-32 degrees C (29-30 degrees C for milk and white). Seeding with tempered chocolate achieves the same result. Bad temper gives streaks, dullness and weak snap.
Worked example. A batch is smooth and well-tempered but tastes flat and slightly sour. Refining is adequate, so suspect over-conching after a long, hot roast. A lighter roast with shorter, cooler conching usually recovers the fruit.
Traps. Assuming more conching is always better; roasting by the clock rather than by smell and taste; confusing viscosity (flow) with particle size (texture); tempering milk chocolate at dark-chocolate temperatures.