Roasting: Q & A

Below are a few more specifics about roasting, outlined in question and answer form.  I came up with a few that I thought would couple well with the previous post.  But, please comment if you have any of your own!

How long does a roast take?

It is generally recommended that a roast take between 12 – 20 minutes depending on the roaster.  For the Diedrich, a roast shorter than 13 minutes will likely have been roasted at too high of a heat, and a roast longer than 18 minutes probably over baked the beans.  Negative effects of over or under roasting include charcoal flavor, lack of flavor or a general dullness.

How high of heat is needed to complete a roast?

Many roasters have a temperature gauge installed to read either the bean temp or ambient temp.

• An accurate read of the bean temp during the roast is impossible unless it remains still.  And ambient temp readings can be altered by a change in airflow, addition of new cool green beans (at the beginning of the roast) and when a shaft is opened to check the appearance of the beans mid-roast.  Ultimately, this makes both types of temp readings on roasters slightly inaccurate.

From my experience roasting on Diedra, with Hawaiian coffee beans (low grown, high moisture), these are the general ranges of temperatures we use during roasting.  The roaster is heated up to a temp between 360 – 420 degrees F.  The beans are ‘charged’ (dropped in to the drum), and there is an immediate drop in temp.  Sometimes this temp can drop as low as 160 degrees F.  As the roaster heats back up, from existing ambient temp and applied heat, the chemical changes begin. Along the roughly fifteen minute ride, the color gradually darkens to a dark brown.  Depending on the degree of roast desired, the bean will be ‘discharged’ (released from the drum – halting the roast) somewhere between 410 and 460 degrees.  The color changes more rapidly at the end of the roast, and a few degrees difference can make the difference between a medium and a dark roast.

The images below are bean samples of the same roast, extracted at four different temperatures.  They are each about 7 degrees apart, and are in order from lightest to darkest.  These coffees will be part of a cupping (at least 24 hrs later) to identify the best discharge temp for these beans.  Any guesses on what type of beans these are?? Hint: I’m not referring to their origin.

 

Do all beans react the same in the roaster?

Definitely not! In fact different batches of the same coffee, from the same fields (from different sections or tree varietals) can vary greatly from each other. That being said, there are clues to look for before jumping into the first roast of a new coffee.:

• Bean origin (country, region, farm)
• Moisture content (ideal 12%)
• Elevation of farm (lower grown – softer bean, higher grown – harder bean)
• Age of bean (old crops almost always are more dull, and reversely, very new beans that have not stabilized during Reposo can react very unpredictably)

Considering these variables is important for creating your plan when approaching the first roast.  But what’s necessary is to respond quickly if the beans are roasting too fast or slow.  As agility is respected in a roaster, it is the aim to control the roast, rather than react.

If you have any more questions about roasting, please ask! This topic can get very science-y and detailed, so I won’t throw too much your way just yet.  As this will be a core part of our business in the very near future, I expect us to dig deeper into this subject in the future.