When you make the decision to automate the coffee roasting process in your plant, one of the biggest things to determine is your flow rate of coffee to and from your roasters.  Failing to properly assess your capacity needs could result in production bottlenecks that handicap your ability to roast efficiently.

Read on to take a deeper look at how BURNS approaches the implementation of conveyors into a coffee roasting system…

Calculating Conveyor Capacities

At first glance, this dilemma feels easy to tackle. Let us look at an example from a recent customer inquiry about upgrading their plant. The customer has a 120kg roaster with a capacity of about 0.5 tons of green coffee per hour. The roaster is currently comfortably loaded and unloaded by conveyor systems with capacities of 1.5 tons per hour each (see Figure 1). They want to purchase a new BURNS B540R roaster (with a capacity of about 1 ton per hour) and assumed they would be able to control the flow adequately with their current setup.  

Figure 1: System Before BURNS B540R Expansion

Breaking it Down

Looking into the specific batch sizes for both roasters, we can see that, with 1.5 tons per hour conveyor systems, the feed rate for the 120kg is about 5 minutes 15 seconds per batch. The feed rate for the B540R (240kg) is about 10 minutes 40 seconds per batch. Both these machines can run at 4 batches per hour, but the total time it would take to feed them with the current conveyor system is roughly 64 minutes. Not only is it not possible, but this estimate assumes the conveyor can be loaded instantly, which is not the case.

Loading the Roaster

Loading the roaster is a more complicated process than it initially seems. Usually, a conveyor will be transporting coffee from a weigh scale to the roasters to ensure proper batch sizing. You will need to empty the scale completely before you can start weighing the next batch. Therefore, you need higher conveyance rates to keep up with the roaster capacities. Each case can be a little different, but a safe bet is to have a conveyor that can transfer about one batch every 3 minutes. Not only does this estimate account for weighing the coffee, but it also leaves a little bit of cushion for future expansion.

Unloading the Roaster

Unloading the roaster is much simpler than its counterpart. Since the coffee has already been weighed, the conveyor is only dependent on the roaster itself. However, there is still a need for a higher capacity than the roaster. For example, if you follow up a full batch in the roaster with a smaller, quicker one, you will lose time waiting for the conveyor to finish emptying the roaster. For unloading, BURNS usually uses a transfer rate of roughly one full batch every 5 minutes.

Now that we have taken a deeper look into the conveyor systems that surround the roaster, we can properly assess the capacities needed for our customer. Our estimates come out to about 5.5 tons per hour to load the roasters and 3.5 tons per hour to unload the roasters (see Figure 2).

Figure 2: System After the BURNS B540R Expansion

With optimal estimates, you can begin to search for the right conveyors to automate your plant. Of course, there are also plenty of ways to adjust these estimates, such as adding a two-tier weigh scale or multiple conveyors. These are some of the many ways our BURNS engineers tackle automation issues daily, and they are always available to you for free, no-obligation consultation. To schedule a call with one of our experts contact us at https://www.burnsroasters.com/contact/ .


  • sstouffer says:

    HI Burns, in your article you discuss a scale prior to the roasters to ensure the appropriate weight of green coffee is transferred to the roasters. You also discuss weighing the roasted coffee in the section, “unloading the roaster”. With these 2 values can you automatically calculate shrink, or will I need to keep a spreadsheet to calculate shrink myself?

    • jlapres says:

      Hi sstouffer, that’s a great question!

      Burns offers plant controls solutions when we set up coffee roasting plants for our customers. Not only will our plant controls track and calculate the shrinkage on each batch you roast, the controls also offer plenty of other data tracking and visualization options. This way, you can customize the system to show exactly what you want to see. Please give us a call if you want to hear more about what Burns can do for you!


Leave a Reply