Knowing at what temperatures roasting events take place is the foundation for planning and controlling a roast. Just like any 'cooking' activity, temperature is just one factor which helps you predict what is going to happen next and at what rate it is approaching. Aroma is another. An experienced cook knows, by aroma alone, that the oatmeal cookies are about one minuite from being ready to take out of the oven. Based on so many different factors, you decide what change, if any, should be made and when the 'cooking' is done.
    When it comes to roasting coffee, no two different types or different brands of roasters will show the same exact temperatures for events except by coincidence. There is a long list of factors which cause that:
  • Depth of bean mass. A Hottop has a depth of, at the most, two inches. A large, commercial gas roaster which can handle over 300 pounds of beans at a time may have a bean mass depth measured in feet!
  • Type of thermocouple used and its placement. Different types of thermocouples react at different speeds. 
  • Calibration of the electronics interpreting the data.
  • Type of drum. A perforated drum may have a different effect on displayed temperature than a solid drum
  • Distance from heating source. A small, perforated drum with a shallow bean mass may create a greater, direct exposure to the heating source than a solid drum.
    When I compare my experience with Hottop roasters to my experience with my 700 gram capacity gas roaster,  the temperatures of events disagree by around 50 degrees! There are a lot of factors for this discrepancy as I described above. Does that mean that one roaster or the other has a design flaw or is defective? No! All that matters is that any given roasting event in any given roaster should always take place at a predictable temperature point. If a roaster displays a temperature of 395 degrees at the beginning of second crack, then that roaster should do so for every roast with only the slightest difference. Air temperature, humidity, bean moisture level, and bean density all play a part, but we are only talking about a few degrees difference.

     In general, your Hottop should see 1st crack beginning at approximately 350F and 2nd crack at approximately 395F. Is stress the word approximately.because even these are just general guidelines. To begin with, some beans start a 'crack event' like racers off the starting line when the gun sounds. Some will begin with a click here and a snap there, and slowly increase in the frequency of the cracks. So when do you mark the beginning of such an event? It does not matter so long as you do so about the same way for each roast of that bean or blend. One solution is count the number of snaps, and for example, mark the beginning of first crack after ten of those sounds. Some beans have distinctive beginnings of these event, and other varieties of beans will begin a crack at a more leisurely pace.

     As your roasting knowledge increases you will be able to use clues other than just temperature to predict events. The color of the beans and the aroma and volume of the smoke are two examples. As the sum of this knowledge increases through experience, so will your skill as a home roaster.