Colors of Coffee Beans During Roasting

Roasting is one of the most significant aspects of making good quality espresso. It is also the reason for one of the more dramatic changes a coffee bean undergoes. Not only does the colour of it change from green to dark brown or black, it also dramatically changes size, weight, density and chemical make-up. This article highlights some of the color changes a coffee bean undergoes during the roasting process.

Green

All roasting begins with tiny, hard green beans. The beans come from the seed from the coffee plant’s cherry. Each cherry has between one and three beans inside, but two beans per cherry is most usual. Green coffee has already been dried and processed in the country that the coffee was produced (the production country). These green beans are wrapped in a silver skin that is mostly removed during roasting. When the Green Beans are dropped into the roaster, the roaster’s temperature will quickly drop and then begin to slowly rise.

Yellow

After a couple of minutes the beans will lighten in color and become yellow or orange. The coffee bean is losing moisture and absorbing heat. Because they are absorbing heat, the beans are considered to be endothermic. The beans will show a consistent pale yellow color that progressively becomes darker.

Tan

As the coffee beans warm up chemical reactions begin inside the bean. Sugars begin caramelizing, which can be seen by the beans becoming a deeper tan color with a blotchy surface. These chemical reactions generate co2 that builds up inside of the cells of the coffee subscriptionsbean. The gas is under high pressure and causes the bean to expand somewhat. Due to this expansion, the silver skin coating gets broken and begins to come off. This substance is called chaff and you will see it mixing in along with the espresso beans.

Brown

While the caramelization proceeds the beans become darker and more even in color and new flavor compounds are made by a process generally known as Maillard reactions. The surface of the bean will become wrinkled. Co2 continues to be created and the pressure builds within the bean as it approaches first crack.

First Crack

Here the pressure of gas inside the bean becomes too much and the bean cracks as the gas is discharged. The beans greatly grow in size and while in first crack the beans give off heat (making them exothermic) but afterwards they return to absorbing heat. The internal temperature of the beans is approximately 355°F when first crack begins.

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