Peaberry is a tricky one. This is going to sound like a lot of soft science, but this is what I've gathered from my experience:

While the bean is smaller and denser, the shape doesn't allow them to lay together as closely, which increases the volume of your batch. To observe this, take two containers of the same size and put a "flat bean" coffee of similar density (my mind goes to washed coffees from Ethiopia or Costa Rica) and put a specific weight in one. Then put the same weight of peaberry in the other container. There should be a noticeable difference in volume. This creates an interesting situation since the coffee is dense but because the coffee bed isn't as tight and the shape is odd, conductive heat transfer isn't as effective.

I'm not sure what your typical washed vs. natural vs. semi-washed processes are like, but my approach has been to treat peaberry like something between a washed and a natural: a lower charge temp to avoid scorching since it is still a dense coffee and slightly higher gas and airflow settings over the course of the roast since convection is going to play a larger part in heat transfer (relative to a normal washed coffee). Depending on what size machine you're using, you may also benefit from decreasing your batch size slightly, assuming you normally run at max capacity or close to it.

Also, this is a separate thing, but for the sake of your sanity: Tanzania is still getting it's bearings in terms of specialty coffee. While the country has the right environment and grows a lot of nice varieties of coffee plant, flavor can still be a little bit of a crapshoot and I can only attribute this to things on the harvesting and processing side. I've had peaberry lots with limited traceability and brilliant tasting notes and others that have been less than brilliant no matter my approach to roasting them. Visually, the coffees have all been well sorted, both in terms of size and defects, and relatively fresh in terms of harvest date. It's just the chemistry that ended up being very, very different despite being labeled "Tanzanian Peaberry". So, all that to say: do your best to work out the roast profile, taste critically, and manage your expectations. The potential for an exceptional coffee may not be there, but you could end up with a real gem.

Hi Mick

Great Question! I wish I had a great answer;-) hopefully my tips will help.

The first peaberries I roasted I used my classic East African light roast profile. This wasn't a successful roast. The cup came out overly acidic, vegetal flavors, thinner body, dryness, and overall lacking sweetness. So then I had to open up my profile possibilities to account for this lack of drinkability. What I found is....

1. Longer slower roasts provide more balance and sweetness.

2. Lower charge temperature aids in longer roast and initial energy input not being so high to over roast outer bean.

3. Longer Dry and Mid phase compared to regular beans allow energy to penetrate the much thicker peaberry.

4. Development phase same as normal East African light roasts.

5. Example roast plan-

370 F charge temperature, air @ Low, Fuel @ ? (to get to end of dry at goal time), 5:30 to green to yellow, 9:45 to 1st crack, plus 2:00-2:30-drop at end of 1st C or within 30 sec of end of 1st C. That would be for a Light Med roast.

That is where I would start. If you let me know a little more what you want out of this green I can help dial the profile in our at least give suggestions to aid in success.

Good Luck! Cheers!

Derek DeLaPaz