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The Effects of Roasting on Coffee Beans

By: Rex Inego | Jul 01, 2011 05:50 AM

The raw and fresh green beans are not used to prepare coffee. The reason is it does not have the flavour or the aroma that roasted coffee have. How does roasting change the coffee in taste and what are the changes that occur to the green coffee beans? Roasting coffee changes from green to yellow and then on to brown. The chemical and the physical constitution of the bean, changes with each roasting step. The green unroasted coffee beans contains acid, and caffeine, but the flavour and the aroma is yet packed and sealed which has to be extracted. The method of roasting involves Maillards reaction, where in amino acids and reducing sugar reacts to release flavour and aroma. The coffee beans are first sorted to remove the unwanted debris before roasting. Commercial roasters are horizontal and uses heat between 370 and 540 °F (188 and 282 °C), for up to 3 minutes to even 20 minutes. The source of heat used can be gas, electricity or wood. The heat applied can be direct or indirect which adds its difference to the taste. The mass scale roasting uses Turbo Roaster, which is not preferred by coffee connoisseurs. Roasting coffee occurs in stages. The endothermic change is the first where the green bean slowly turns yellow. The next step occurs at 205 °C when the beans increase in size to almost double and cracks. At this stage the coffee changes to light brown. Between 205 °C and 220 °C the colour deepens further. Finally between 225-230°C, the colour changes to dark brown and cracks again with an external oily sheen. Many people like it roasted dark and stronger. Thus coffee roasting is what decides the flavour.




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