Steaming of coffee within NKG-Kala
Description of the main process steps
Steaming is a method for the quality improvement of raw coffee by treatment with steam made from water at elevated temperature and elevated pressure.
Step 1. Moisturizing of green coffee
Raw coffee flows from the silo to a vessel where it is treated with saturated water steam for around 30 minutes with temperature going up to 95°C. There is no pressure and the moisture level of coffee raises to 22%.
Step 2. Treatment under steam and pressure
The humidified coffee flows to the Extractor where it is treated by water steam again but under a pressure between 1 -5.5 bar and a temperature of max. 160°C.
Step 3. Drying
Then the coffee is going into the dryer. The dryer rotates constantly. Inside the dryer there are hot plates which are heated by water steam up to a temperature of about 65°C. Coffee being placed into the dryer is loosing humidity. The humidity is going out of the system by vacuum. The drying step terminates when coffee reaches the pre-calculated weight positioned on the weighing scale. As soon as it is achieved, the drying is stopped and the product falls out of the dryer into the cooling system.
Step 4. Cooling
During falling into the vessel the coffee is cooled down by air which is blowed through a sieve through the coffee bed. The temperature should be 30°C.
Then the process is finished and the coffee goes back to the silo.
The physical appearance is effected and the raw coffee comes out of the process much darker. Due to the temperature during the process ingredients of the coffee beans are metabolized, leading to a creation of new substances, leading to precursors of different aroma-and flavor-components.
Chemically, carbohydrats and proteins are reacting, polyphenolic acids will be metabolized and depending on the process conditions a new and different acidity profile after roasting will be initiated.
Roasting times are reduced.