Category: Articles

Roast Development in an RK Drum

Article borrowed with permission from Seth Newsome. Please visit his excellent Blog. Thanks Seth!

We’ve celebrated our third month in business and are staring our fourth right straight square in the face.  During this time, I’ve had to overcome the learning curve of roasting coffee on a five burner gas grill converted into a coffee roaster while nailing down the roast development necessary to make great coffee.

This learning curve has been helped considerably by Shane Lewis at RK Drums who I can’t speak more highly of.  Shane has been instrumental in helping me understand the how to roast coffee on a somewhat less than conventional and often quite finicky device intended for burning burgers and charring chicken breasts.

Nonetheless, I’ve come across some recent discoveries that may assist other RK Drum roasters in creating a more consistent product from batch to batch while eliminating some of the less desirable qualities of that somewhat finicky device.

Time and Temperature

The essential function of all coffee roasting is time and temperature.  Pro roasters will incinerate me (and probably Shane) for saying that internal bean temperatures are not necessary for producing an excellent, quality, and consistent roast.  Nevertheless, Shane, along with the company’s creator Ron Kyle, developed a simple time and temperature chart for their drums where under a given temperature and green coffee load a coffee should reach first and second crack at a certain time.


roast development rk drum

A snippet of the 12 pound drum roast profile chart from RK Drums. You can find the full chart as well as the charts for all of the RK Drums here.

However I, along with many other roasters, find that the time and temperature chart is merely a guideline and more often than not does not align in the slightest with what my temperamental roaster wants to do in any given day.  With that said, I did some research and developed a system that seems to work really well for our machine and our coffees.

More Roast Development

While I can’t with any confidence express that I’m an expert in roasting, roasting techniques, nor roasting coffee beyond a brown, grindable, drinkable substance we call “coffee”, I’ve sufficiently studied some roasting techniques in order to better understand how professional roasters roast great coffee time and time again.

I stumbled across the Cat & Cloud podcast above with the Czar of modern coffee, Scott Rao, which really turned me on to exploring more technical aspects of our roast.  While Rao’s “textbook” on coffee, The Coffee Roaster’s Companionis one of the predominant texts for coffee roasters and enthusiasts, his article, Roast Development Time and the Prerequisite for Any Successful Roast, published on the Daily Coffee News really shines a clean albeit simple light onto the process of roast development.

In Rao’s article, he mentions that great, memorable coffee has two consistent characteristics that stand out from roast to roast.  One, Rao says, is that coffee hits first crack at 75-80% of the roast and the coffee develops 20-25% of the total roast time.  In layman’s terms, the time between roast start to first crack should consume 75-80% of the roast while the time after first crack starts should be 20-25% of the roast.

Rao’s Roast Development on an RK Drum

While Shane’s chart is a great starting place, my numbers almost never line up.  Depending on how the roaster decides to heat on any given day and various ambient factors, I’ve had to adjust accordingly on our RK setup.

For roaster’s looking to improve and measure a roast on an RK Drum, the simple way of doing so is recording the time of first crack’s start* and using some simple division to calculate an approximate development time and when to pull a roast to optimize origin character and roastiness.  Using this method will negate any external factors that may be affecting your roast and allows the roaster using an RK Drum to make realtime calculations on their roast.

rk drum roast development

Our 12 lb. RK Drums setup on a 5 burner propane grill.

Let’s use an example from Shane’s chart in the paragraph’s above.

Take a look at the 4 lb. example in Shane’s chart.  According to his chart, we should be hitting first crack at approximately 10 minutes.  Assuming that we are hitting first crack at 10 minutes, using Rao’s methodology, we can divide our first crack time by .80 and .75 respectively to give us a range for when to pull our roast.

Using the formula 10 ÷ .80 and 10 ÷ .75 we get a range of 12:30 and 13:20.  Meaning, our coffee has developed for 20% of the roast at 12:30 and 25% at 13:20.  But if we look at Shane’s chart, a 4 lb. roast should hit 2nd crack at 12:00 which is a little too long for an evenly developed roast and at risk for hitting second crack.  Ipso facto, I generally adjust my constants in my equation to .85 and .80 respectively.

Using the constants of .85 and .80, assuming we hit our first crack at 10:00 as per Shane’s chart, we can create the following formulas for our development range: 10 ÷ .85 and 10 ÷ .80 giving us a range of 11:45 and 12:30.  With that said, we can be watching to pull our roast within the timeframe of 11:45 – 12:30 total roast time.  If everything stays on Shane’s schedule, you would be pulling your coffee a fuzz before 2nd crack making a very developed, well-roasted, flavorful coffee while eliminating some of the guesswork involved in your roast.

*For the longest time, I marked the start of first crack when first crack started “rolling”.  In other words – when the beans were popping and cracking in rapid succession.  While measuring first crack’s start is somewhat arbitrary, Rao suggests measuring first crack, “the moment [you] hear more than one or two isolated cracks.”  If you measure differently, you may need to adjust your constants accordingly.

Some Notes on Roast Development

While this formula works well for most applications and adapts to your roast for the day, it isn’t the end-all be-all for home roasters.  There is certainly room for variation, but this formula is adaptable to any roast.  If your roaster is running fast, the formula adapts accordingly.  If the roaster is running slow, that is accounted for as well.

Roast development really doesn’t have to be rocket science, but far too often we make it just that.  The problem I’ve always run into is mastering the art of “guesstimation”.  I’ve always played guessing games with the development of our coffee in the roaster and made assumptions as to when and how well it’s developed.  With this method, I’ve seen far more consistent roasts and far more consistency in the cup.

As for Shane and RK, I can’t say enough good about the quality of the equipment, the personal service, and dedication to perfection that Shane displays even months after my initial purchase.  Shane even called me on a Sunday afternoon prior to a family obligation!  Now that’s service of the best kind!

I’m interested to know how others have been able applied this or similar tactics to help predict their roasts on RK equipment, so please leave comments down below.  If needed, I can always publish a followup piece that explores additional methodology.

Manual Hand Crank Rotisserie Available (Manual)

These manual rotisseries are ideal if you plan not to use a motor, for if you are roasting manually for show, or for other reasons.  Buy this if you don’t plan to use a motor or wish to use a motor at a later time.

It’s a bit more expensive than the standard rotisserie due to the number of steps to fabricate, as well as the materials involved to make it functional.  Note that the crank handle is a turning handle and the main shaft handle is fixed for easy grip.

Part 3: Putting it all together during the roast.

Before diving into this article, please have a read of the previous two prerequisite sections, Part 1 (Understanding the roast process….Heat vs. Mass) and Part 2 (What happens during the coffee roast process…).

So much like in the 1st part of this article, understanding heat vs mass, is critical to understanding how to properly roast.  Roasting coffee is exactly like boiling a pot of water, except instead of a pot, we have a drum and instead of water, we have beans with water in them.  If you understand the pot-water-boiling experiments in the 1st article, then you can understand easily what is happening inside the bean.  

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Part 2: What happens during the coffee roast process…

Let’s look at what coffee roasting is, and should be…

What happens during the ideal roast…

First of all coffee is a seed, of the arabica or robusta tree….  it generally has between 9-14% water inside of it.  Yes, the same kind of water in our pots in the 4 experiments above.  When we roast the coffee, at a certain point, that water reaches the boiling point and begins to escape the bean with an audible low-volume “POP”.  This commonly sounds the same as popcorn in the microwave popping, just lower volume.  This is commonly what people refer to as 1st crack.  It’s generally one of two indicators of the status of our roast.  As the water boils away from the bean, and as we keep heating it, the bean begins to caramelize and the structure of the bean begins to expand, and stretch as the internal sugars begin to caramelize.  This builds up stress in the bean to at which point the bean’s shell fractures and cracks.  This cracking can be

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