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How to Reduce the Smokiness during Coffee Roasting

Author: Lei Zhang

Editor: Kelvin & Amir


How to Reduce the Smokiness during Coffee Roasting

When I began to learn how to roast coffee, I found that I would have the same problem as many other roasters—smoky flavors would always find their way into my beans.  

Whenever you roast, the silver skins burn off, and the result would be a smokiness in the coffee.  However, this smokiness can be reduced during the resting period after a batch is roasted.

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( Credit Alex Jones )

This had always been my understanding, until I took a course by Dr. Manuel, one of SCI’s founding members.

Dr. Manuel emphasized the idea that unless you’re in second crack, there really isn’t any smoke.  There were some improper “standard” or “traditional” roasting methods that needed to be updated.

The other students and I couldn’t understand at first, but by the end of the SCI course, all of our question had been answered.  Following are some of the big questions I had, and the answers I found during my time studying with Dr. Manuel.

1、Silver Skin Burning will Produce a lot of Smoke

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( Credit Square One Coffee Roasters )

In the early stages of the roast process, the silver skin inside the bean will not fall off so quickly, but the silver skin exposed on the outside will come off and get sucked into the silver skin collector.  

A small amount of this will combust, but the smoke produced will only pass over the surface of the coffee bean.

(Note: The silver skin inside the bean won’t burn away until the bean has reached medium or dark roast. These silver skins are what we find sometimes find among coffee grounds.)

And so we find that, actually, the silver skins burning off is not a major factor, and some of these smokey notes will disappear within a few hours after the roast.

2、Where Do the Strong Smokey Notes Come From?

But this answer only led us to more questions.

The structure of coffee beans are very fibrous, so at a certain temperature the bean will begin to burn and carbonize.  And so, if the silver skins did not burn out, how could the fibrous structure burn?

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( Credit Killer Roasting Co. )

To answer this new question, we need to understand a bit more about “traditional” roasting methods.

Most roasters will use high temperatures during the roast, or start with a high charge temperature, especially when using beans with a high moisture content.  This is intended to accelerate the dehydration process so as to avoid a “baked”, dull flavor in the cup.

However, there are some problems with method, and one of the symptoms is the smoky flavor that we find in the cup.

However, this method is wrong and one of the main reasons for smoke.

3、How can we know that this is the problem?

We know that the heat transfer inside the coffee beans is conducted primarily through the free water between the cells.  

Consider the example of boiling water on a stove.  If the kettle is first heated up with a big fire, some of the water will immediately vaporize when added, but as more water is added, the temperature rise will not be as sharp.

This same principle can be applied to coffee beans.  When we set a high charge temperature and drop the beans into the drum, the water on the outside will quickly absorb heat, vaporize and dissipate.  

This will reduce the temperature inside the drum and delay the transfer of heat inside the beans.  This will have a few impacts on the roast:

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( Credit Damian Krzywoń )

1,First, there will be a large difference in the temperature on the surface of the coffee beans and inside.  When a roast is completed, we may find that the surface has been roasted to the desired color, but the inside is relatively under-roasted, or underdeveloped.

2,This issue is further exacerbated by the heat from the steam acting on the surface of the coffee bean.  The fibrous structures of the bean also lose water content, burning more easily, resulting in a more carbon-like flavor.

The result is a smoky flavor in the cup, even in a medium or light roast coffee.  This smokiness will take a long resting time to fade, and it is nearly impossible to remove completely.

So how can we avoid this from happening?  During the SCI roasting course, we focused on one key principle: medium to medium-low heat will more evenly transfer heat inside the coffee beans, resulting in a more balanced roast.

We recommend trying a relatively lower charge temperature for your roast profiles—the results may surprise you!

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( Credit Kris Krug via Flickr )

Of course, there are many other factors that can result in a smoky flavor in the cup.  These include the air flow, the timing of adjusting the heat, control of the Rate of Rise (RoR).  We will cover these topics later in other posts.

It is important to remind everyone here to also properly clean and care for your roaster, as this can also result in some unwanted smokiness.

Some people might ask, “what if my beans are not fresh?” or “if the moisture content is too high, or the density is too low, what problem might this produce?”  These and other topics will be covered in our SCI courses, as well as future posts.

I hope you all found this article useful and informative!  See you next time!

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