Brazil Natural - strange behavior

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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#1: Post by ShotClock »

I'm not sure if this is due to inexperience or incompetence, and I'd appreciate the advice of HB. Roasting my first Brazilian natural with data logging, I've had a very difficult time with a big dip in BT ROR just before DE. Below is one of my better attempts, although obviously not great.

I tried changing the charge temp, first gas setting after soak, and duration of soak, but with quite limited success. I also had a similar issue recently with a wet hulled Sumatran, but was able to tame it much better by manipulating the gas levels.

I also noticed a few curves showing hints of the same behavior on the recent roast and learn thread here, in the last couple of posts. Nothing so extreme as my own curves though.

Is this a known issue with Brazilian naturals? Any tips to help reduce or eliminate these dips?

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#2: Post by Trjelenc »

I've seen these before and my thought has been that the only reason why the dip happens is because the peak RoR is artificially high, and the dip is simply the RoR coming down to the "real" rate.

Remember, the turning point is simply the point where the dropping temp of the BT probe intersects the rising temp of the bean mass. After that, there's a short period of quick RoR rise as the bean mass and BT probe continue together as the temp reading goes back to the charge energy minus the energy the room temp beans absorbed. This is just the probe seeing a fast temp increase. At a certain point, that initial acceleration goes away and the RoR drops down to the real acceleration of the bean temp beyond that initial part of the roast. What graphically becomes a plummet is just the stark contrast of that initial "probe reading" spike and the lower RoR of the rest of the roast.

If you reduced charge temp you might find you max out at a lower RoR but stabilize down to a similar number, creating a smoother downslope.

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#3: Post by OldmatefromOZ »

Try a little hotter charge temp with less airflow, which might need slightly less gas. Many Brazil nat can take quite a bit of heat at the start, its once they start browning things can become a bit tricky and they will take off / bake.