In November of 2024 I wrote “How to Scale from a 6KG to a 20KG,” to act as a resource to transfer roast profiles. We still use the methods laid out in this blog today, but over the years we get questions from scaling businesses asking for more clarity on expected roast times and percentages in phases. It got me thinking that this blog needed a follow up. We are going to explore the reality of roast times as you scale, how percentages can be both helpful and misleading, and tips to get more consistent with batch sizing.
ROAST TIME EXPECTATIONS
Average roast times can be anywhere from 8-15 minutes. This is a good guideline, and works for many commercial roasters. However, it does not take into account the capacity of your machine.
If most of your career as a coffee roaster is on a smaller machine, those roast times might be expectations you carry to the larger machine. When scaling, you are going to learn a new baseline for times that produce successful roast profiles you identify on the cupping table. A good expectation to set is that roast times will increase when you are roasting at max capacity. If you are struggling to get calibrated at longer roast times, decreasing your batch size can help you find familiar lengths of time spent roasting your batch.
DEVELOPMENT TIME RATIO (DTR)
This is the percentage of total roast time spent after first crack in the development phase. An average range in percentage for light to dark roasts can be 15% - 30%. In the best scenarios, this piece of data helps roasters hit their roast profiles with consistency. In the worst cases, roasters have put coffee in the trash right out of the cooling tray because it was off on percentage points. Don’t do this. This metric is a guideline, not a rule.
|
Total Roast time |
9:00 |
15:00 |
|
Development time with 20% DTR |
1:48 |
3:00 |
Development time ratio percentage isn’t the most useful metric when scaling, instead focus on the time in the development phase to your desired finish temperature to get a consistent flavor profile. As shown above, your time spent in development will change depending on total roast time. When you lock in profiles by confirming them at the cupping table, your development time ratio finally becomes a metric you can rely on in relation to that batch size, on that machine.
ROAST CONSISTENT BATCHES
After you install a new machine, roasting full batches can be intimidating. It is a lot of coffee, and adds up to a lot of money. It can feel better to start at a 50-60% batch size until you are comfortable working your profiles larger or smaller as you learn your new machine. Once you are versed in the capacity you are working with, making standard batch sizes will help improve consistency and roast profiles to reference. For example, If I had a 15 kilogram roaster, I would make three standard batch sizes.
|
Batch Size |
Green Coffee In (lbs) |
Roasted Coffee Out (lbs) |
|
Large |
30 |
25 |
|
Medium |
18 |
15 |
|
Small |
12 |
10 |
The strategy is that large batches are for blends and crowd pleasing single origins that sell at volume. Medium batches allow space to finesse roasts that may require more particular adjustments. Small batch sizes are great for limited time coffees that run at higher price points and lower volume coffees.
IN CONCLUSION
Coffee roasting theory is something we should always come back to. As the industry continues to grow, new methodology and processes get shared, but it may not always be the best fit for your roasting style. As coffee roasters, we get to decide what theory works best for scaling our business and the quality we are working to achieve.
