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Coffee: The Magic Roast- How and why coffee beans are roasted

Updated on November 13, 2010

Despite the accidental hurling of coffee beans into the fire in the 9th Century, it wasn't until 300 years later that coffee-lovers realized that roasting was such a vital (even magical) means of achieving great coffee flavor.

In the 16th Century, the roasting of coffee was actually prohibited, though this was most likely simply another reason to close down the "seditious" coffee­houses. One commentary on the Holy Koran of the time reads "Whatsoever reaches the level of carbonization, that is, becomes charcoal, is absolutely forbidden."

That was something of an aberration in the history of coffee. But even before roasting became habitual in the 15th Century, the coffee pit was eaten, fermented, turned into either wine or butter. Still, it is universally agreed today that the perfect flavor begins only with the alchemy of perfect roasting. And the word alchemy isn't used lightly here. For contemporary scientists are still unable to chemically analyze some of the processes which take place during roasting: it is still a magical roast.

One would imagine that with such a "mundane" process, one would use only mundane words. But when coffee experts discuss roasting, they talk about "the moment of truth", "the mysterious chemistry", "the rush of the aroma" and the head shaman or magician of the whole process, the Roast Master.

Why roast coffee beans in the first place?

Because without roasting, the bean won't give up its flavor. Professional tasters may find something of value in the green bean, but coffee-drinkers are only interested in the roasting process.

What exactly happens in the roasting process?

Nobody knows the complete story yet. But one can have an idea by knowing something of the composition of a green coffee bean. The bean is composed of water, oils, protein, caffeine, chlorogenic acid, trigonelline, tannin, caffetannin, caffeic acid, sucrose, starch, acid and vitamins. And all of these are changed during roasting.

Physically the coffee changes in three ways: when the steam, carbon dioxide and carbon monoxide are released, the weight loss can be between 14 to 23 per cent. But before miserly coffee-buyers have time to regret this, remember that the internal pressure of the gas expands the volume of the bean by 30 to 100 per cent!

The third physical aspect of change is the color. Depending upon the length of roasting, the bean will change from green to brown, all of this controlled by the Roast Master. Depending upon its later use, the bean can go from green to light brown to deep rich brown to near-black. Chemically, this is due to the sucrose caramelizing on the outside.

The most important aspect is the taste and aroma. And nobody can explain this thoroughly.

When the aromatic hydrocarbons are roasted, they turn to a kind of taste-stimulating acid, which, with the caffeine (which doesn't change), produces the pleasant bitter taste. Already, a mystery emerges here. For, as the acids are created, they are also destroyed. Because of the time difference, it would seem that a light-roasted coffee would have the most acid and, in theory, would have the most flavor. But it is not so. For, along with the acids, there are other flavor-inducing substances. Tannin and caffeine also provide an astringency and pleasant taste. So does the trigonelline, though nobody is yet certain what this adds.

The aroma is equally important, and equally mysterious. No less than seventy different chemical compounds have been traced which give off that seductive aroma. But nobody is yet certain exactly what happens. All that the Roast Master knows for certain is that, when the oils are released in the roasting, when (to simplify it to one basic) the carbon dioxide is produced with the chemicals, then the aroma comes out, and the Roast Master has found the "moment of truth", or the "volatilization" of the bean. At this point, the roast should be done and ready for packing after cooling.

If the chemistry is complicated, the mechanics are... well, mechanical. For commercial uses, there are only two basic ways of roasting the bean, and both resemble a kind of spin-dryer.

In the oldest method, coffee in a metal cylinder is roasted above a source of heat: charcoal, gas or electricity, with the temperatures raised to about 220-230 degrees C. This is called singeing. The more common method is to put the beans in a cylinder and blow hot air onto them, gradually raising the heat until the beans are done.

The normal time, depending on what sort of roast is needed, can be between 7 to 18 minutes. And the beans are so sensitive that nobody can leave them to cool on their own. Once they reach the optimum "moment of truth", the beans must be taken out and laid on a cool substance (like marble), and/or sprayed with cool water. Otherwise, they could continue to bake by themselves.

What are the different kinds of coffee roasts?

Basically there are only four:

a. Light roast: This is a delicate roast, and the coffee is good for breakfast, blending excellently with milk and sugar.

b. Medium roast: A stronger coffee, close to the way the French like their coffee.

c. Dark roast: Spanish and Cuban coffee is roasted like this. It does give a "darker" smokier flavor.

d. Double/Continental/Espresso: Almost black, ready to make espresso or Turkish-type coffee.

Does coffee have to be roasted by a Roast Master with a huge cylinder?

Not necessarily. It does make things easy and practical. But for those who take their coffee ritual seriously, one can roast green beans right on the kitchen stove, with much practice and probably very little success at first.

One should use a very heavy frying pan. One puts a single layer of beans in the pan, roasting them on a medium slow fire, then a quick high heat towards the end. The pan must be shaken continuously, and the beans must be turned constantly to assure an even roast. The fire must be stopped just before the optimum color needed.

Or one can use a roasting tin in the oven. The tin should be placed in a pretty hot oven for 20 to 40 minutes, depending on whether light or dark roast is needed.

The advantages are not all that great. But one might have some sense of satisfaction and one might imitate the Ethiopians, who throw the most aromatic spices in with the beans just at the end of roasting. Cloves, cinnamon, nutmeg, fennel, cardamom (my own favorite) and ginger. These are ground up with the beans.

In Europe, the French sometimes add roast sugar, and the Italians add a little butter with sugar to the beans.

The most important part is to cool the beans immediately, and then seal them in an air-tight glass container. Remember that the beans may start losing their flavor just as soon as they are roasted. But this can be slowed down considerably with the right kind of container.

And when ready for brewing, one takes the beans out for the equally important grinding process.


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    • Myn Is Me profile imageAUTHOR

      Myn Is Me 

      8 years ago

      Thank goodness for that! Imagine losing the sense of the sweet aroma of those coffee beans. It would be a tragedy!

    • dallaswriter profile image


      8 years ago from North Carolina

      Myn is Me,

      There is NO POINT where you can't spell the coffee beans. I can't speak for others but I don't smoke so I have a very sensitive nose. I think the best part of it is walking in about 4 am (we opened at 5 am) and it was like a "welcoming hug". And when you own your coffee shop, there is no such thing as not enough. I could drink coffee morning, noon and night, espresso too. I don't think it has any effect on me. Others though may be more sensitive. Perhaps oneday I will be opened for business again.. Until then... :) :)

    • dallaswriter profile image


      8 years ago from North Carolina


      Wish I still had my coffee shop and you and yours could come, visit, laugh and write. If you are having coffee and I get to share that time with you, I am honored and glad. My your cup runneth over all day:):)

    • Myn Is Me profile imageAUTHOR

      Myn Is Me 

      8 years ago

      Coffee and hubs go so well together!

      And I notice that you refer to your wake-up "pot" of coffee and not "cup" of coffee lol. :D

    • epigramman profile image


      8 years ago's funny because as I am leaving you a comment I am having my wake-up pot of coffee which starts my day and it's called Italiano espresso - and this really is a definitive hub subject on coffee - bravo to you for a job well done and I raise a cup of 'joe' to you ...

    • Myn Is Me profile imageAUTHOR

      Myn Is Me 

      8 years ago

      I know in some jobs people can't smell what it is they work with, like baking bread every day or working in a chocolate factory. Is it the same with coffee? Is there a point where the roasting process just doesn't give you the same sort of high as you get as a mere coffee consumer?

    • dallaswriter profile image


      8 years ago from North Carolina

      Great job! I use to own my own coffee shop and I am a coffee junkie! In the process of deciding if I want to do it again and even do my own roasting this time. Enjoyed this. :)

    • Myn Is Me profile imageAUTHOR

      Myn Is Me 

      8 years ago

      Thank you! I don't come here nearly often enuff. So a belated Xmas and also hoping you've had a good start to the new year!

    • Cheeky Girl profile image

      Cassandra Mantis 

      8 years ago from UK and Nerujenia

      This is amazing and being a total coffee fanatic I loved this naturally. I know too much coffee is bad for me but screw it. LOL! Great hub, Myn. I enjoyed reading this! Cheers! Happy Christmas from moi! :D


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