How to Roast Coffee

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Machine Management

HTR 2.01 Batch Size

The first steps in roasting coffee are deciding the size of the batch you want to roast and weighing out the green beans. To make it as easy as possible to maintain consistent warm-up and roasting procedures, we recommend choosing just one or two different batch sizes to work with. In this lesson, we’ll help you decide what batch sizes you should choose to meet your needs.

Weighing out a batch of beans into an automatic green coffee loader

Roasting multiple batch sizes greatly adds to the complexity of your roasting procedure. It’s virtually impossible to create roast profiles for different batch sizes of the same coffee that give identical results. Each batch size requires a specific amount of thermal energy in the roaster, which means each batch size needs a specific warm-up procedure and between-batch protocol to ensure consistent results. Depending on your roaster design, different batch sizes may also require different drum speed and airflow settings.

Keeping all of these settings optimised as the air temperature and humidity change and the green coffee ages is already a lot of work; doing so for multiple batch sizes is nearly impossible. For this reason, we recommend choosing the smallest number of different batch sizes that you possibly can and roasting only one batch size per session. In other words, if you choose one batch size for your espresso blends and a smaller batch size for your single-origin filter roasts, try to roast all of your single-origin coffees on the same day. If you must roast different batch sizes in the same session, roast the smaller batches first, because they need less thermal energy from the machine.


Realistic Maximum Batch Size

In a traditional, single-pass drum roaster (which doesn’t recirculate hot air through the drum), the largest batch size you can roast while still maintaining good quality is determined by the capacity of your machine’s burners. We discussed this point in Lesson 0.05, where we explained how to choose a machine with enough capacity to meet your needs.