When green beans enter the roast drum from the top hopper, they are at room temperature. Releasing the green beans into the drum therefore leads to a drop of the temperature curve. This is called the turning point.
From the turning point (typically for us between 50-70 seconds after releasing the greens) temperatures go up. Both the gas/burner temperature and the air flow that pulls hot air through the drum, define the roast curve. Hitting the right turning point is vital - it defines the length and rise rates along the whole roast curve.
At The Barn we have very tight parameters for any deviation - roasts that fall outside our pre-set tolerances will not be used or sent out to customers. While some tiny deviations are allowed, they are few as going into First Crack even 10 seconds early will change the roast result. Roast consistency is absolutely key for us.