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How are coffee beans roasted?

Roasting, in itself, is an age-old technique. Probably derived by our ancestors accidentally dropping something onto a fire and rescuing it, only to discover it made it better.

From here, it’s estimated that roasting became a favoured technique, in the 15th century, after metal roasting pans with long handles were designed to be able to roast and retrieve safely.

Previously, we looked at why coffee beans are roasted, unveiling the different flavour profiles created and some of the scientific occurrences, during the coffee roasting phase. Now, we’re going to take a closer look at the stages and techniques required to roast coffee.

What do you need to roast coffee? 

Industrially, a large scale coffee roastery is required. Huge roasting drums are required to toast the coffee beans to the desired level, accompanied by both man and machine to operate it all successfully.

As the drum rotates, either gas or electricity heats the tumbling beans from below. There are other types of roasters such as air roasters but each coffee roaster will have their preferences depending on their recipe.

Other infrastructure would include a green coffee intake area, contingency roasters, packing lines, development kitchens, cooling areas and all the power to supply it!

Roasting coffee at home can be done in a variety of ways and can be quite simple. The only equipment you really need is a large roasting pan. The only problem is volume. It is important to have experience before attempting roasting coffee at home.

What happens to the coffee beans during the roasting process?

Depending on how long you roast the coffee beans for, and your desired outcome, there are lots of incidents that can occur throughout the coffee roasting process. Each stage can either be determined or identified by the colouring of the bean or a common occurrence.

As the beans roast, in temperatures roaring anywhere between 180 degrees to a 210, colouration of the coffee bean spans from a natural green to an extremely dark brown. What’s more is that the extreme temperatures cause reactions within the bean, making them pop and crack!

Roasting curve

What are the stages of coffee roasting?

Green coffee bean phase

Altering from a green to a pale green, if not almost white, suggests that the coffee beans have had a very short amount of time in the roaster. The aroma will be very raw and grass-like. Although the beans are absorbing plenty of heat, there are no major identifiers to note. The coffee beans at this stage are not drinkable.

Yellow coffee bean phase 

By the time the seeds hit around 150 degrees centigrade, reducing sugars react with amino acids and produce a non-enzymatic browning. This is what begins to transform the coffee bean form a pale green into a yellow. You will notice the smell alter too and become more hay-like.

Tan coffee bean phase 

Now that the coffee beans have reached around 165 degrees centigrade, they will begin to caramelise, producing an orangey/light brown colour to the bean, along with a sweet smell, much unlike the previous aromas. At this point, you know your beans are not too far away from becoming something more like the coffee beans we are used to seeing.

Coffee bean first crack

Much like popcorn, coffee beans pop or crack, after a sustained period at a certain temperature. The ‘first crack’ is a tell-tale sign that the coffee beans are roasted enough to be ground and brewed. The nature of the crack may be swift and loud or much slower and longer. This will help you to determine what you do next; it’s what you do next that will influence the final outcome of your coffee and its flavour.

Coffee bean development time 

How long you leave the coffee beans to roast after the first crack and when you choose to stop is up to you. What a lot of people don’t realise is that even an extra 30 seconds can impact upon the final flavour profile of the coffee.

A shorter development time generally produces a more acidic flavour whereas longer roast make room for more bitterness.

Coffee bean second crack 

If the roast continues long enough, a second ‘crack’ will occur. The second crack of the coffee bean is never as distinguishable as the first and happens as the oils begin to escape. It’s at this point where the ‘roast’ flavours begin to over power that of the origin, becoming less acidic in doing so.

If you take the bean much further than the second crack and you’ll be left with burnt beans which are utterly undesirable.

Cooling the coffee beans

Cooling the bean back to room temperature as quickly as possible is key. Leaving the coffee too hot for too long will develop the roast and lessen the flavours.

To get the coffee beans cool, vacuum systems are employed or something known as ‘quenching’ via the mist process. Alternatively, beans can be released from the roasting drum to a cooling chamber. The coffee beans are rotated to keep them evenly distributed and fed air through small holes to reduce their temperature. 

From here, maintaining freshness is critical for some recipes. It’s not uncommon for the roast coffee beans to be packed straight into foil packaging (with gas release) and shipped, to obtain optimum freshness.

Roasting Coffee Beans

Roasting coffee at Lincoln & York

Lincoln & York operate two state-of-the-art coffee roasteries. Between them, they house six Brambati S.p.A coffee roasters and 14 packing lines. As our equipment ranges from a 30kg specialty roaster up to 600kg, we can fulfil orders from 60kg to 6,000kg and beyond.

We are proud to be the only large roaster in the UK to have our own on site contingency facility, offering ultimate reliability and total flexibility to all customers.

Our team of operators monitor all roasts in person, not only checking the progress on our robust computer system but by sight and smell.

For any further information, please get in touch.

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