We were asked, “Is there a simple formula to maximize sweetness for these coffees?” “I can control time between cracks easily, but not temperature”
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… No, not a formula – maybe a rule of thumb. Just don’t roast too darkly. easy as that. You want to hit second crack so the sugars caramelize just a little but not so much that you burn them up. The rule of thumb to hang on to the sweetness is, err light.
Another rule of thumb is in the timing mentioned in the question, between 1st and 2nd, if you can extend that a little you gain a bit of body at the expense of snappiness in the cup. But, extend it too long and you wind up with flat tasting coffee.
Working it the other way, if you’ve got a naturally big bodied coffee you can get more brightness out of it by going hot and fast, but at the cost of some of that body.
We’re not a fan of recipes with numbers attached. They’re not real. They are not easily reproducible in home machines and far too subjective. You’d need to have a NASA lab to do something the same way twice roasting by numbers (or at least a $10,000 roaster with data logging.) The very best thing you’ve got going are your own senses and that’s FREE. Use your eyes, ears and nose, and just pay attention. Thats better than an army of number crunchers. With a few iterations you’ll hit on what you like and be able to get pretty close time after time.
It all comes down to “more of this is less of that.” and “Less of that is more of this.” Its actually all pretty easy. Rule of thumb: just pay attention.