Coffee flavor is effected by many factors,roasting is the most critical factor. coffee valve would like to tell you roasting is a kind of chemical change under high temperature,it can thoroughly change the material inside of the coffee bean,produces new compound and recombine to bring out the aroma and flavor that is locked inside the green bean.
Roasting is both an art and a science,is has very deep knowledge.So the roasters in Europe countries and America have a high reputation if they are skillful and experienced in roasting. Generally,coffee roasting has three stages.
At the beginning of the roasting,the coffee bean is start to absorb heat,the moisture of the water is evaporated gradually.During this stage,the color of coffee bean turn to yellow or light brown from light green.The silver skin comes off and the coffee bean release a kind of light herbal flavors.The main function of this stage is remove the moisture from the coffee bean,it usually takes half of time of the whole roasting procedure.The coffee roasters would take full advantage of the temperature of the moisture and control carefully to prevent from too fast evaporation.Usually,the time the moisture reach the boil and turn to steam is controlled in the 10th minute,because the inside material is roasted,the moisture is evaporated and starts to rush out.
Step 2.High temperature decomposition
When the roasting temperature is up to about 160℃，the moisture inside is evaporated to steam and starts to rush out.In this time,the inside coffee bean turn to release heat from absorb heat,the first cracking appears.After the cracking,the coffee turn to absorb heat again,the inside pressure is very high,it is equal to 25par air pressure.The high temperature and high pressure broke the original structure and produce new compound that create the wonderful aroma and flavor of coffee.When the temperature reach 190℃，the transition happen again between absorb heat and release heat,then the second cracking appears.Of course,the high temperature decomposition is go on,the color of coffee transfer into dark brown from brown,the heavy roasting stage comes.
After roasting,the coffee need to be cooled immediately to stop the high temperature decomposition and lock the aroma and flavor.Otherwise,the high temperature decomposition will go on to burn the aroma flavor that would lead to bad flavor.There are two kinds of ways to cool the coffee bean,one is air method and the other is water method.Cool method requires lots of cold air from the air fan to reduce the temperature of the coffee bean quickly within 5 minutes.The water method is slower than air method,but it’s very clean and do not have any pollution.In addition to this advantage,the water method can protect the aroma and flavor more effectively.Therefor,many roasters who produce special coffee prefer to use this way.How to use water method to reduce the temperature is spray a layer of spray on the coffee bean to cool the coffee quickly.