Troubleshooting & Tips for New Roasters

It happens to the best of us – whether the temperature was too high, the batch was left in for too long, or fate just had it out for you today, your beans are charred and oily coming out of the roaster. While you can’t bring a burnt batch back to life, we know some strategies that should help make the next round a different story.

First of all, always observe and log as much about the roast as you can such as temperature, color, time and batch size. The goal is to achieve a relatively consistent rise in temperature throughout the length of the roast until the end (aka "drop") temperature is achieved. That ending temperature is arguably the most important factor that will affect the taste in your final cup because it is directly tied to how light or dark of a roast you'll end up with. If the finish temperature is too high, the beans will be visibly darker than your grandpas favorite coffee so dialing back that ending temperature should be your first place to start.

“But I’m using a popcorn popper (or cast iron pan) – I don’t have a great gauge on my heat,” you might say. Check out our blog on the best home roasting equipment for some guidance on upgrades available for your popcorn popper and other tools such as a roast color card which can help you get those temps consistent without buying a whole new roaster.

If you're noticing a few beans in your batches that look way darker than the rest, you might want to consider "contact time", that's literally how long beans are touching a hot surface. Decreasing the batch size (which we'll get into later) can often help give those beans more room to move around in a popcorn popper, in a drum roaster you may want to consider adjusting your drum speed faster. And if you're roasting in a cast iron pan the solution is simple, stir them more! (If your arm gets sore from pan roasting them, it means you're doing it right, the beans should never be still.)

Once you have a handle on the finish temperature for your desired profile(s) (light, medium, dark) the outside color of the beans should to look fairly consistent from batch to batch. If the temperature and color of the beans are coming out as expected but the flavor is off, it's likely that timing is the issue.

A batch of coffee can take anywhere from 7-14 minutes on average depending on the equipment, batch size, and of course roast level. That is a pretty wide range so finding your sweet spot will take some trial and error but here is a strategy that can help.

1. Set a target ending temperature/color (roast level)

2. Roast a few batches to that desired ending temp, making the temperature increase faster in some batches, and slower in some batches. (and don't forget to take notes)

3. Evaluate and taste

Some indicators that a roast was too fast are if the inside of the beans are less roasted than the outside. This indicates that there was not adequate time for heat to penetrate the bean fully leaving the surface roasted, but the inside under roasted. In the cup this may taste grassy and over acidic.

If the roast was too slow, you'll notice that the coffee lacks complexity and has very low acidity. This flavor is often described as Baked.

The single most important takeaway from this whole section is writing down as many details as you can when you hit a roast you like – and only changing one variable at a time when you try to fix any issues. We’re big fans of Cropster for roasting data management. Logging your roasts in a roast log book like this one can be a simpler way to maintain your data.

Sometimes home coffee roasters want to run before they can walk. On their third batch, they’re already looking for unique flavor notes or roasting as many different green coffees as they can get their hands on.

There’s really no substitute for experience. Take your time and experiment with various temperatures, lengths, levels of roast, and so on. Cup your batch and try it. Then try it again compared to the next one. Never quit in the middle of a batch or just randomly decide one of your roasts is was a dud.

You got into this because you’re passionate about it, right? Nobody is born good at… well, practically anything, but especially coffee roasting. Tasty coffee will happen as you better understand your equipment and notice which steps of the process you’re still a little shaky on. Speaking of which…

We already talked about writing stuff down, right? Well this takes it a step further. Have a process – especially in the form of a checklist – that you follow whenever a batch wraps up. Maintaining a consistent BBP helps ensure the same starting conditions for each batch you roast by resetting the thermal energy of the roaster between roasts. This ensures that each batch begins at the same temperature, which is crucial to consistency across batches.

Sounds like a lot, right? Don’t worry, we’ve got an example for you. Here’s a basic BBP:

Weigh your resulting beans. Work out the ratio of how much weight you’ve lost (we mean your beans – you probably weigh about the same as you did 10 minutes ago). Double-check that you didn’t miss any measurements on your last roast; it’s okay if you did, just don’t make stuff up. The variable you didn’t track becomes the one that you’ll tweak next time.

Clearly label the batch you just worked on to match it with your notes in the future. Maybe give it a person’s name. Something like Bruce. You’ll taste-test Bruce 24-72 hours from now, but don't taste-test prior to 24 hours after roasting for best results.

After that, clean your roaster. Then clean your surrounding workspace. Organize your tools nearby so you’ll know where to find them at a moment's notice. Now you can start heating up your roaster while you weigh out some green beans (a.k.a. Bruce’s brother, Craig).

A good BBP will save you so many headaches down the line and help you improve faster. This is a pretty nerdy hobby, so lean into the science – while still remembering to keep it fun. Maybe tomorrow, when you pour out a mug of Bruce, you’ll hate him to death while your spouse thinks he’s neat.

Your roaster probably has a recommended range of green beans you can load it with, unless you made it yourself. Be prepared to find out this estimate is either a bit high or low – especially based on your other variables and your intended roast intensity. As a rule of thumb, 40% of your roaster’s capacity is the minimum. Best results are often found at around 80% of the roaster’s size.

Overloading a roaster generally gives you bland results – since you’ll have to roast everything for longer, and even that still won’t draw out maximal flavor. Underloading generally gets you a low yield of shriveled beans. It can also negatively impact the temperature data you’re collecting from your roaster. When you underload, the thermometer inside may not be fully surrounded by beans, causing it to read the air temperature rather than the bean temperature.

You know the drill: to confirm which is the case, keep the temperature, time, drum speed (and maybe even the socks you wore) the same, just use a slightly higher or slightly lower volume of beans.

Your beans don’t have feelings, and they don’t play favorites. If something went sideways in a batch, chances are it was an accident, but you should be able to pinpoint the cause by isolating a single variable and testing it.

That’s it! We’re rooting for you. Keep on learning, keep tasting, and keep coming back to our blog page for help when you could use it. In the meantime, why not check out our Specialty Coffee Ambassador Nick and his continuing quest for coffee knowledge (he helped us with some of the facts in this article)? There’s also this blog full of new roaster FAQs. Alright, that’s actually it.