Flavour

Coffee Roasting Methods | Drum Roasting vs Hot Air Roasting

What happens when you roast coffee?

The coffee roasting process is complex. When you begin to roast green coffee, a lot of changes begin to happen. Coffee starts green and pales to yellow, then into brown as the Maillard Reaction kicks in. This is when reducing sugars and amino acids react to form aroma and flavour (this is how we take a flavourless, rock-hard seed and transform it into everyone’s favourite morning ritual).

As roasting continues, moisture inside the beans begins to evaporate. This builds up a lot of energy which is forced to explode outwards, creating a cracking sound from the beans. From this point the beans will double in size but lose a fifth of their weight as they shed a layer of skin known as chaff. As we roast past the first crack, we can develop and highlight a variety of flavours depending on how far we want to take it. As with a lot of things when it comes to coffee, it’s a personal preference as to how much we let the coffee develop and roast, changing the result and experience.

What’s the difference between a light and dark roast coffee?

How long you roast and develop coffee also affects what you taste in the cup. Roasting with a shortened development phase past the first crack will result in brighter, more acidic coffee; this light roast style brings out a lot more citrus, floral and herbal notes in coffee.

When we develop past this point, sugars in the coffee begin to caramelise, enhancing the sweetness in the coffee. Developing further, we begin to roast darker and bring out more body from our coffee, at the expense of acidity and sweetness. Go even further with a roast and you will eventually hear a second crack, which will result in very oily, roasty flavours dominating the experience.

The delicate balance between acidity, sweetness and body is what we strive for with all our coffee, which is complex when every coffee around the world is different. The best thing about coffee is that there is no right or wrong way when it comes to flavour.

We’ve always felt sweet, clean flavour is superior to anything else and that’s what we stand for. But it really does come down to personal preference, so get drinking and find your favourites!

What are the different methods for roasting Coffee?

Two main roasting methods are used for this coffee transformation: the traditional Drum Roaster method and Hot Air Roasting. At Allpress, we Hot Air Roast our coffee, so we’re a little biased when it comes to coffee roasting methods.

Drum Roasting

(As the name suggests) is a large drum rotating over a heat source, roasting the coffee as beans meet the hot metal. With coffee rumbling around a drum, inconsistencies are rife. There’s no-where for the shedding chaff to escape, hotspots are scorched onto the beans as chaff begins to stick and burn up on the hot, metal drum. This can result in plumes of smoke escaping the roaster when it’s opened and an underlying smoky taste to the overall roast. With drum roasted coffee, every bag you buy and every cup you brew will be slightly different from the last.

But if you get a delicious coffee from a drum roaster, know that it takes a lot of care, skill and precision to achieve that flavour!

Hot Air Roasting

This more modern approach eliminates the undesirable effects of drum roasting. With Hot Air Roasting, coffee is suspended in a convection current of hot air. This hot air envelops every single bean evenly; unique characteristics of the coffee can be expressed as we achieve a consistent roast every single time.

The precision of Hot Air roasting relies on temperature control sensors more sophisticated than what you find on a drum roaster. The sensor in an air roaster is accurately gauging the real time temperature of the coffee as it is undergoing these flavour changes. This allows our roasters to have superior control of the roast, taking the coffee to the very edge of flavour development, without compromising on the sweet, clean flavours. This differs from a drum roaster’s temperature sensor which is monitoring the air temperature, not the drum temperature where the coffee is roasting on the hot metal. Inconsistent temperature readings can result in hotspots and poorly developed roasts.

As the coffee cracks and expands, chaff is pulled from the roasting chamber, so you’ll never get any undesirable smoky flavours from Hot Air Roasting. A medium roast with one hundred kilos of coffee will take twelve to fourteen minutes in our ART Roaster. Once a roast is completed and roasted coffee is being spread out on the cooling tray, we use recycled hot air for subsequent roasts so we’re not consuming tonnes of energy to heat the whole system up every time we start a roast.

Flavour impacts of your coffee roasting method

These different roasting methods have huge impacts on how coffee develops and the end taste you get in your cup.

Traditional drum roasting coffee is what’s called a conductive heat transfer. This roasting process brings out the carbohydrates and oils in coffee, leaving you with a thicker, denser flavour and aftertaste. Regardless of what origin is being roasted, there will always be heavier, oilier flavours punching through.

Hot Air Roasting uses a convective heat transfer to roast coffee. Convective heat transfer elevates the aromatics in coffee, resulting in a sweet, clean flavour consistently. Hot Air Roasting coffee will result in a pleasant aftertaste that you want hanging around for the day! Sweet, clean flavour is what we’re known for, and our Hot Air Roasting is how we achieve it.

Which is better- Drum roasted coffee or Hot Air Roasted coffee?

At Allpress we’ve always felt sweet, clean, consistent flavour is superior to anything else and that’s what we stand for. The Hot Air Roasting method allows us to control the roast throughout the entire process and nail the flavour profiles we set out to achieve every time. Drum roasting will always hold a soft spot for the traditionalists out there but ask us and we’ll always favour the results of Hot Air Roasting’s superiority.