Pay attention to smell. Once you’ve entered first crack, you’ll notice a sweet, almost vinegar-like aroma. This is a sign that your coffee is sufficiently developed - of course, you can roast darker if you’d like, depending on preference. Be sure to move past the yeasty, bready aromas noticeable in the drying stage or you might under-roast - this is particularly important if you’re aiming for a lighter, City/City+ roast with a decaf coffee.