Between Two Batches: the Secret For Consistent Roasting

Reflecting on my time behind the roaster–many hundreds of coffees known on intimate terms, tens of thousands of roasts, countless careful tweaks to profiles and anxious cuppings to see if changes to temperature or time yielded positive results, there was one breakthrough, one big win, that stands out above all other highlights.

It’s not the nailed roasts of $100+ per pound Panama Geshas, or wins in roasting competitions. It’s something far less sexy but so incredibly important: the development, a number of years ago, of an über-reliable and methodical protocol for cooling down the roaster between roasts. What is now known (shoutout to Scott Rao) as a Between Batch Protocol (BBP). Sounds lame, I know. But when you’ve spent years chasing your tail struggling to follow profiles and then one day–like magic–your roasts track beautifully, you don’t quickly forget it.

It’s an opportune time to discuss this often overlooked part of roasting, seeing as Cropster released automatic recording of the time between roasts as part of their software update late last year (read more about that here).

A Cropster profile with the between-batch temperature recorded (in the grey section).

So let’s get into the details. How do you craft an effective between batch protocol?

1. Understand why you need one.

If you are clear on the logic behind cooling cycles (i.e BBPs), then devising and modifying your own becomes far easier.

As you roast coffee, you apply a lot of heat to the roaster. If your roast involves a batch size that’s up to or more than half the roaster’s capacity, chances are that you’re hitting those beans with all the gas you’ve got at the beginning of the roast, or close to it. While much of that heat energy is absorbed by the coffee, it is also absorbed by the roasting drum and faceplate (with Loring roasters being somewhat of an exception–this article applies mostly to conventional drum roasters). This means that unless you cool down between roasts, your roaster will keep getting hotter and hotter, and your beans will start roasting faster and faster. Not good.

Another issue occurs when you switch from roasting, say, 4.5kg on a 5kg roaster to 2kg. Different batch sizes require different amount of energy input. Accordingly, a 4.5kg roast leaves the roaster hotter directly after you’ve spilled the beans than a 2kg roast does.

Clearly, then, you want to achieve a between batch protocol that allows you to return the temperature of the roaster’s components to a stable baseline that doesn’t vary regardless of how many roasts you do or what your batch size is. So how do you do it?

2. Temperature is key (not time!)

For a long time, the standard cooling cycle process involved dropping the roast, turning off the gas, waiting a set amount of time (say, a minute), then starting up the roaster again. This system sucks.

If your goal is to reach an equilibrium temperature, then focus on temperature! This is great because it means that the time between roasts self-corrects depending on how hot the roast was. If you’ve just completed a large batch dark roast, reaching the equilibrium will take longer than if you just roasted a small batch filter roast. Focus on temperature, and time will take care of itself! Same goes for hot days / cold days.

A Basic Between-Batch Protocol Framework

So what does an effective between batch protocol look like? Let’s get to it.

1. Once your beans are out turn gas to zero.
   –this may seem obvious, but I’ve seen cool-down protocols that, for mysterious reasons, involved keeping the gas on. Unless you want to take a toilet break, it’s probably a bad idea.
2. If your roaster is small (less than 15kg) consider reducing your airflow. If it’s big (60–90kg) consider increasing it..
   –on a small roaster, reducing airflow allows you to reach a temperature equilibrium without cooling the roaster too much. On a large roaster, boosting the airflow helps cool the roaster down more (which is often what you want).
   –if you choose to change your airflow, make sure you choose a very precise way to do it: to a specific notch on an airflow damper, or to a particular fan speed. We need to control all variables!
3. Close roaster door at a pre-determined temperature
   -depending on your probe thickness, it will cool in the ambient environment at different rates. See what the temperature is around 30 seconds after dumping the last roast, round to the near 10 degrees, and pick that as a starting point (e.g. 140C after dumping a coffee at 205C).
   -when you close the door, the temperature is going to shoot up again. That’s cool. That’s what we want.
4. Cool down the roaster to a pre-determined temperature level
   -after the temperature of the roaster climbs post-closing the door, it will start dropping again (duh. The gas is still off). Now we pick our final cool-down temperature.
   -the trick for this is picking a number that doesn’t take too long to get to (less than 5 minutes) but is low enough that the temperature of the roaster isn’t rapidly cooling past the number. So if you choose, say, 145C, it should take at least a couple of minutes to get there and not whizz past it on the cool-down, but not get stuck for 3 mins at 152C and arrive at 145C 12 mins later.
5. Fire up, baby!
   -Gas on! Set your gas to whatever your starting gas setting is, and don’t forget to reset your airflow!!

That’s it! This is a simple and very effective method for keeping your roasts tracing their profiles again and again.

If you’re brand new to roasting and want to learn the ropes, check out our the ECRE Academy Roaster Maker course! It’s a one-day intensive that is designed to equip you with the necessary foundational theory and practice to get yourself roasting at home or commercially.

Written by Tuli Keidar