What’s the right amount of Coffee to Roast at a time?
There’s the old adage, “The Bigger The Better”. And seeing as though many of us roasters are time poor, the bigger the amount we roast the better. If our roaster can roast 400g, we’re definitely going to be roasting 400g minimum! But unfortunately, this is one of those situations where bigger isn’t always better. Bigger might be better for time efficiency, but it can make the quality of our roasting worse. Just because our roaster can fit 400g physically doesn’t mean that’s the ideal size for getting the best out or roaster.
If our batch size is too big, we won’t have enough heat. More beans need more heat. Which can mean a couple of things can happen:
- Our roast will take longer and will be easier to stall which can bake your coffee (think flat savoury flavours instead of sweet, bright and pleasantly acidic).
- The heat won’t be enough to get to the inside of your bean which will mean even though the outside is developed, the inside won’t (think grassy and vegetal flavours).
- Roasts can be uneven. There are more pockets for the beans to hide away from the heat source and can get stuck there meaning some beans will have roasted while others haven’t.
The ideal batch size will depend on what you’re roasting with. It’s drum size, airflow and heat output all come into play. But as a ballpark figure, have a go with roasting 50-75% of what the stated capacity is. If there’s no stated capacity (I’m thinking popcorn machines and bread makers), aim for about 50-75% of what you can physically fit and keep moving consistently. Roast durations should ideally take anywhere from 7-15 mins depending on what roast your aiming for.
For example, we currently have a 10kg roaster and roast 7.5kg batches for Milk Based and Espresso Coffees and 5kg batches for Filter Coffees. These batch sizes enable us to get plenty of heat at the start of our roasts to get proper development of sugars and acids.
It might take a bit of trial and error for you. And it might mean you have to roast a little more frequently. But it will be worth it.