Did you know green beans are also kind of blue? And that something called “the crack” is one of the most important parts of roasting? Come with us and we’ll show you all the sights, sounds and smells of roasting day at Black Sheep. As Mark says, “It’s part science, part art and skill. And a little magic and romance thrown in…”
In the beginning, green beans don’t look or smell anything like roasted coffee beans. They’re pale green with a touch of blue and the raw beans are small and hard.
The first thing we do is to turn on the gas cylinders and fire up the roaster. Ours is a beautifully designed traditional style drum roaster made by the Giesen family in Holland.
The roasting drum starts spinning, the airflow whirrs and the pilot light clicks over. Then the main burner comes to life with a hot, blue flame. This is the roaster’s heating up stage. It will get to 220 degrees Celsius, with the temperature probes and computer idling around the desired temperature. It takes about 30 minutes to heat up before the first batch can go in.
The beans are carefully weighed out into metal buckets and lined up in sequence to be roasted. Then they’re loaded into the hopper where they fall into the rotating drum of the roasting chamber.
Inside the drum the temperature is 215 degrees, but with the 15kg of cold green beans that quickly drops to around 105. It slowly climbs again and this is known as the “turn point”. It’s one of the markers in the roast that needs to be consistent, so the roast profile (or roast curve) stays the same.
Every roaster or coffee company has a different method for achieving the exact roast they want. Depending on their equipment and what they’re trying to achieve — body and depth, heavy syrupy flavours, natural light fruit sweetness — they might roast slower or for longer. Our beans roast for about 13 – 13.5 minutes.
The “trier" or bean sampler on the front of the roaster reaches right into the middle of the spinning beans so you can inspect a few grams closely, under daylight, throughout the roast. The kinds of things we’re looking at are the different stages of roast/bean colour, the smell, and the bean size and texture.
The first few minutes of roasting is the drying out phase. The beans are slowly heated and their natural moisture evaporates. Then they start to change to a pale straw colour. At this point they smell like wet dough. Next they turn light brown and smell like hay or straw.
Now the beans will swell to almost double their size. They’ll have a smooth, even appearance in colour. From here the colour starts to change from light brown (which smells like freshly cooked toast) to mid brown, then dark brown and if taken further, a very dark brown to eventually black.
Around this stage, we’re listening for the first crack. This is a very important stage of the roast.
The beans have many layers and fibres. Trapped inside the layers are air pockets and these expand under the heat. As they do, they hit a critical point in temperature and crack open. It almost sounds like corn popping. You can actually see the spilt or crack on the ends of the beans and the centre line opening up.
Depending on the type of roaster and bean profile, this can happen at different times. For us, this first crack happens at approximately 188 degrees. Just before first crack, the gas is turned right down to make sure we don't overshoot and roast too fast before the beans drop.
Anything after first crack to when the beans are dropped out into the cooling tray is called "RD" which stands for Roast Development Time. There’s a general consensus among the roasting community that the RD needs to be around 25 per cent of the overall time, in order to achieve maximum flavour and body.
The second crack begins to happen at the mid brown and dark brown stage of the roast, around 200 degrees. There are several minutes between first and second crack and during this time the flavours, body and natural sugars have time to caramelise.
At 201 degrees the door is opened and the beans come tumbling out with a small trail of smoke. As they hit the cooling tray, the cracks and pops of the second crack start.
The freshly roasted beans are cooled and stirred simultaneously. Hot air is sucked from the beans via a fan located under the cooling tray. The beans need to be cooled within the first two minutes so they don't keep on roasting.
Then they’re bagged up and ready to begin the next part of their journey to your cup.