Roasting 102

Rate of Rise, Roasting 102

Now that you have fully mastered Roasting 101, let’s move on to roasting with attention to rate of rise. We will use Fahrenheit throughout the discussion.

Rate of rise, you say?  Don’t make it more difficult than it is.  Rate of rise is merely tracking and roasting with an eye on the amount of degrees the bean (BT) is rising in any particular time frame. Some roasters use 30 intervals; we will use 60 seconds — or how much is BT going up in one minute. Delta BT = Bean’s current temp minus bean’s temp one minute ago. 

Why bother?  Lots of ways to roast but I favor a declining rate of rise (ROR). I find that by using this approach, it will give you the best development and sweetness the bean has to offer without baking out those flavors. So on with the show.

Remember from Roasting 101:

• Drop temp around 400, amount equal to roaster capacity
• Do not turn the burners off on 3K and above roasters. With 1K and 2K roasters, you may have to turn off the burners for 60 or so seconds.
• Air initially set for lowest airflow which keeps fan engaged. What is low? Use a cigarette lighter at the trier throat.  A setting of low should have a slight bend in the flame direction, into the roaster.
• You want to have the roast with a ROR between 32-35 degrees for about 1.5 minutes and then let the ROR slope downwards.
• At end of drying  ~ 5 min (yellow/no green hues), turn up your air to medium. At medium, the flame should lay right down into the throat.
• Your milestone for first crack (FC) is 8-10 min. Roasters at 3K and above, target 9-11 min for FC.
• Gas turned down 10-15% at about 45 seconds prior to anticipated 1st crack. Remember, this is general guidance. Learn your roaster’s approach. Keep the descending ROR on its natural slope downwards. 
• Turn air speed up to high at 30 seconds prior to anticipated first crack, when the beans in the trier indicate smoke.  High? The lighter will extinguish or come close to extinguishing the air flow. Don’t go higher than this setting.
• Drop when you achieve level or roast desired

A picture is worth a 1000 words so let’s look at a profile which I did on the TJ-067 gas – a Tanzanian peaberry. I ran the ROR a bit above the desired 35 degrees but it cupped well.

  

Lines on the graph?

• Top green one is incoming air temp
• Middle one is red and is the exhaust temp
• Dark blue line is the bean temp
• Bottom bright blue line is the rate of rise in the bean temp (Δ BT).

Bars at the top?  Phases of the roast

• Green bar represents drying phase
• Orange bar is the caramelization phase (Maillard)
• Brown bar is the FC and Beyond phase

Notice the initial spike (blue line) in the Rate of Rise (ROR) at the left of the graph.This is the amount of degrees which the beans absorbed in one minute (ROR). As an example, in this graph, it spiked to 46° at 2 min (too high) and at 4 min, it is at 34,° as read on the right side of the graph.

This is the ROR curve we seek — declining.  This kind of roast profile is called a “declining rate of rise.” 

As one way to roast, I target a 1st crack between 8-10 minutes (my general guidance on 1K and 2K) and this roast had first crack at 9:33. I was after a city roast, which generally comes at 2:00 after 1st crack. Note that the roast was dropped at 11:37 or a 2:04 in the FC and Beyond phase.

Cupping results?  The flavors were a bit muted and it needs more development with more roasting flavor. The next roast, I topped out the ROR at 35*, stretched the roast to 2:20, a city plus roast. Flavors were more developed and more pronounced.

Try the guidance above and tell us about your success!

Dave Borton