Coffee Appreciation

Just out of interest, don't different beans need different timings and heat to get them properly roasted?

I thought there were a couple of stages of cracking, so how is this managed with the pre roast blends?

Individual coffees need different roast recipes or 'profiles' to get the best from them. The profile includes the drop-in temperature, the points at which the airflow is altered, the point when heat is reduced and the drop-out point. Barring a few exceptions cracking occurs within a few degrees whatever coffee you're roasting (first crackle starts between 185 - 188*c on our big machine). The time taken to get to these temperatures is important and is managed by the mass of coffee you load in to the machine, the airflow and the point at which you reduce the heat.

When you are roasting a blend of green coffees you have different densities of coffee. Our Brasil is considerably less dense than the Colombia and Guatemala so one might expect it to reach higher temperatures more quickly, however, what seems to happen is that the beans transfer heat and insulate each other so they behave uniformly. In effect the greater thermal inertia of the more dense beans protects the softer coffee.

We have to stop thinking of the roast as three separate beans being roasted together and think of it as a single entity with a known flavour profile we are trying to achieve. It's not so much a case of trying to strike a happy medium between the three individual roast profiles as trying to do the flavours justice as we would with a single origin coffee.