The Science of Coffee Roasting

The Science of Coffee Roasting

Get enlightened by Sam Chan, the director of NOC’s Roastery

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NOC Coffee Co.  NOC Coffee Co. Where coffee meets design  on 24 Sep '19

For Sam Chan, the director of NOC’s Roastery, the search for the perfect cup of coffee is an exercise in scientific distillation, from sourcing the best beans, to precision roasting through state-of-the-art technology, to NOC’s signature obsession with quality.

We joined Sam at the Roastery’s iconic glass viewing box to learn more about how NOC roasts Hong Kong’s favourite beans.


Tell us about the different origins of the beans NOC uses.

We curate coffee beans from Central American countries like Colombia, Guatemala, El Salvador, Honduras and Costa Rica. We also like coffee beans from East African countries such as Ethiopia, Kenya and Burundi.


Why do you choose these countries?

My roasting team and I prefer coffee with bright acidity and a clean cup. Central American and East African beans usually offer more interesting flavour profiles that we find to have a more crisp finish and a higher level of acidity.


Explain the process you go through to prepare the beans. Which step is the most important and why?

One of the most important steps in preparing the beans is making sure the green beans are always kept in the best condition, ready to be roasted. Green beans are stored in isolation in a separate storage space at our Roastery store. We monitor and maintain the ideal temperature and humidity with the help of a hygrometer and air conditioning.

Apart from preparing the beans, it is also important for us to get the roasting machine ready for the roast. We make sure to warm up the machine at least 60 minutes before we start roasting so that we can accurately control and make changes to the temperature of the machine and coffee beans.

The steps above may seem trivial, but these details really make a difference to the roast and affect the quality and taste of the coffee.

Sam Chan, NOC Roastery Hong Kong


What makes NOC’s roasting method unique from other local roasters?

Our Giesen roasting machines are a hybrid of hot-air and traditional drum-roasting machines. Thanks to the use of convective and conductive heat transfer, we can ensure that each bean is evenly roasted, achieving consistency in roasting level and taste in every bean in each roast batch.

To help roasters to highlight the distinct flavours of different beans, Giesen has designed its machines in a way that allows us to adjust different variables like drum speed, in-drum air pressure and more. This helps us to achieve the ideal roast to highlight the beauty and unique tasting notes of every coffee.


You have said before that the perfect cup of coffee comes down to scientific precision. How do you achieve this and why is it important?

In addition to the Giesen, we use a piece of software called Cropster. This helps us to record our roast profiles, including the different measurements in the roasting machine and the changes to our coffee beans, throughout the process. I love the versatility of the system; not only does it record change in every aspect of the roasting process (temperature, drum pressure, etc) and the roasting curves every time we roast, it even includes a function that helps us to record the inventory of our green beans. Traditionally, roasteries keep track of roasting processes with just pen and paper, meaning there will be errors and omissions in their roasting profile records. This technology allows us to accurately measure and monitor every variable in the roasting profile and is extremely important for us to achieve the ideal roast profile for every coffee we test.

Giesen coffee roasting machine


Walk us through the roasting process. How do you achieve NOC’s signature flavour?

Green beans are actually the seeds of the coffee plant fruit. Because of this, there is a high percentage of water in the beans. The drying stage is when we put the green beans into a heated environment – the roasting drum – so that the water vaporises. As that happens, the green beans become white, then yellow, then brown.

In the latter stage, something known as the Maillard reaction and caramelisation of the coffee beans take place. This chemical process is key for the development of roasted coffee flavour and colour. When coffee beans turn from white to yellow, it means that the Maillard reaction is taking place. This is when the carbonyl groups from sugars and the amino groups in proteins react to form aromatic and acidic compounds. Caramelisation takes place at 170–200°C, and this is when the sucrose in coffee beans browns and dissolves.

As we continue to roast, the beans expand and crack physically and audibly. We call this the first crack, and this takes place at 205°C. This is when most of the chemical reactions in the roasting process happen and marks the beginning of the development stage. The length of the development stage decides the roasting level and flavours of each batch of coffee. If we are going for light roasts, we will release the beans from the roasting drum right after the first crack. If we are going for medium roasts, we will wait for a further chemical reaction called pyrolysis to occur; this takes place at 220°C and leads to the release of carbon dioxide in the beans.

Why do you offer customers the choice between “nutty’’ and “fruity” blends? And can you talk us through how you develop each of these blends?

For the two house blends we offer currently, we curated each blend and roasted it to highlight the tasting notes we would like to achieve with those blends, simplified to nutty and fruity. For the single origins, we wanted to roast in a way that allows the baristas to highlight the different tasting notes that are the results of different farms, process methods and countries.

With the flavour we want to highlight in mind, we experiment with a few batches of coffee at different roasting goals (e.g., roasting duration, roasting rhythm, development time ratio, etc) and cupping to compare which roast we think tastes the best.

How do different roast profiles affect the flavour of the coffee?

As mentioned a few moments ago, the development stage determines the roasting level of a coffee: the longer the duration of the development stage, the darker the roast of coffee. The level of roasting can enormously affect the flavour of coffee. If we roast coffee too lightly, the bitter-tasting compounds won’t degrade; if we roast coffee too darkly, the beans will give the same strong tasting notes of chocolate, nutty and smoky.

The general public still seem to prefer dark-roasted coffee as it tastes stronger and tends to give more of a caffeine jolt. When we created our first house blend, No 34, we wanted to introduce customers to espresso made with medium-roast beans, which might be something new to most people. For customers who still prefer a dark-roasted coffee, we created No 18, our second house blend.

How can customers’ tell whether they are drinking a well-roasted blend?

Different people have different definitions of a good roast. My definition of a well-roasted coffee is one that is not too dark roasted, meaning you can still taste the different tasting notes and characteristics of a specific coffee or blend.

Sam Chan, NOC Roastery Hong Kong


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NOC Coffee Co.

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