The second phase of roasting is accompanied by yet another shorter endothermic phase and a short lived exothermic phase. In the phase a large portion of the free water has been driven and the decomposition of sugars, proteins and lipids begin to take shape. Unlike the first crack which is mainly produced by the formation of steam, in this second crack, the pressure is caused by the formation of CO, CO2, NOx and various other gases.
The exact temperature at which this occurs varies but can generally be seen at about 225°-230°C (437°-446°F). Like the 1st crack there there again is an increase in internal pressure and the beans begin taking on a shinny appearance due to the presence of coffee oils being pushed out to the surface.