What is it? It is simply a log of temperature throughout the duration of roasting procedure. Or a graph showing temperature changes over time. If the resulting graph for specific bean type or blend seems superior then it is saved for future use. The expert roaster together with the microcontroller system tries to replicate it every cycle for a consistent roast quality.
I listed some factors that might affect roast profiling while doing a self study. I think they are not only applicable to coffee and cacao but to all grain that undergo roasting for a reason.
Moisture content. Batch with higher moisture content takes longer time to roast. Those with lower takes shorter time. Batch with beans of uneven moisture content will likely result to uneven roast. There must be a way to quick check the moisture, roast only the batch with the optimum value, dry those with higher and condition the beans with lower.
Bean size. Smaller beans cook faster and larger beans cook slower. Mixing the two is a roasting tragedy. Beans must be pass through a set of standard sieves. Separate roast profile must be developed for each.
Bean defects. Watching the contractors sort the uncountable number of beans one by one tires me. What more if I am the one who is doing it. I imagine myself being very efficient at first, discarding black, broken, empty beans including the none bean components and getting only the good. Then my eyes getting blurry, feeling sleepy, my heads getting achy, causing myself to miss many defects. A machine eye to identify and a mechanical arm to toss off defects would be nice but sure very expensive. Any form of defect ruins the roast.
Variety and origin. Four different coffee varieties have different flavor profiles. Flavor changes in accordance to altitude from where it was grown. Separation and identification is necessary. The same is very true for cocoa. Each variety have different flavor characteristics and requires different roasting profiles which must be developed if not available.
The Roaster. If one can afford, then decision making is easy. Choose the equipment specifically built for the purpose, tried and tested, with the best mechanical design, control system and built with quality materials. Roasting is easier and more accurate with the right choice. Else, it is hard. Roasting on carahay, crude rotating drum over a wood fire and ember. Home roasting styles that often result to raw, burnt, uneven quality.
Some DIYers are able to achieved good roast with home tools like hand drill, hair dryer, popcorn popper. However, they are still for home consumption and not suitable for commercial purposes.
Temperature. As I mentioned above, temperature recording is easy. A thermometer and thermocouple connected to a microcontroller and storage media will do the trick pretty neat. The hard part is temperature control. The data you see on screen is not an actual reading. It is an average of several reads, maybe eight or more. A trick to make it look more accurate. Temperature fluctuates. The heating element should be powered down when the required setting is reached and powered up again when it got below. It seems simple but the temp will not response as you wanted to. It will persistently fluctuate.
As of date, the heating element that could give the best stable heat is the ceramic type infrared heater.