Friday, June 26, 2020

How to Create the Perfect Background Curve

A background curve can act like a set of rails to ride while roasting. Roast masters often use a successful past roast as a reference in the background to follow and reproduce. This can be very helpful. Frequently the roasts available to use as a reference suffer from imperfections like RoR curves that show dips, crashes and flicks. A question we are asked is how to use an existing curve to create a "perfect" reference curve, a curve with straight line declining RoR using the event times and temperatures from an existing curve. This article will show one method to create a such a reference background curve.

1) Start with a curve that has the desired FCs and DROP times and temperatures for the reference background curve.

2) Next, run the Profile Analyzer on this curve. The x² Analyzer option will provide a straight line RoR. Not every curve can be fit this way. If that happens try the x³ option which will provide a smooth declining RoR that has a slight curve to it.

The result is shown below.  The Analyzer performed a curve fit in the time from DRY END to DROP.  This can be seen by the outer shaded area, highlighted by the red box here.  This is the most critical part of the roast.  In drum roasters it follows the time when the probes must adjust to an enormous change in temperature.  They were stable at the CHARGE temperature when all of a sudden they are immersed in beans that are at ambient temperature.  This is typically a change of over 150°C (300°F).

The shaded region is where a linear, declining RoR is desired.  The Analyzer created a background profile with a BT curve that best fits the times and temperatures of the original from DRY END to FCs to DROP, and has a straight line BT RoR.

3) The next step is to bring the new background profile to the foreground.  Use the menu Roast>>Switch Profiles.

A prompt will pop up asking if you want to save the original profile.  Choose Discard (unless you made changes to the original profile that you have not saved and want to keep).  Now the curve fit BT and BT RoR are brought to the foreground.

At this point the BT curve displayed fits the original roast's event times and bean temperatures for the events FCs and DROP.  The BT RoR is a declining  straight line for the most critical part of the roast. 

4) Save the profile to use later as a reference background curve.

Note: This is a good time to save your settings too.  You should save them periodically so if something ever goes wrong you will have a copy to restore.  From the menu choose Help>> Save Settings.

Notice the BT curve is the shape that corresponds to a fluid bed roaster.  Not represented is the initial temperature drop from CHARGE through TP and up to DRY END typical of a drum roaster. When you think about it, the true temperature of the beans starts at the ambient temperature and rises continuously just as shown in this BT curve. While the shape of the BT curve from CHARGE to TP to DRY could be manually recreated in the Designer it is probably not worth the trouble.

If adjustments do need to be made, take the curve into the Designer or use the Transposer (new in Artisan v2.4) to adjust the timings and then repeat the steps above as necessary.

Enjoy creating "perfect" profiles to guide your future roasts.