The Science Of Roasting: How We Curate Our Beans

24 APR 2019

For Sam Chan, NOC’s Director of The Roastery, the search for the perfect cup of coffee is an exercise in scientific distillation; from sourcing the best beans, precision roasting through state of the art technology, and NOC’s signature obsession with quality. We joined Sam in the Roastery’s iconic glass viewing box to learn more about how NOC roasts Hong Kong’s favourite beans.

Hi Sam – to get started, tell us about the different origins of the beans you use.

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 we choose these origins?

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 to make 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 in 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 the coffee beans.

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

The technology allows us to measure accurately 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.

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 roasted evenly, achieving consistency in roasting level and taste in every bean in each roast batch.

To help roasters highlight the distinct flavours of different beans, Giesen have designed their machines in a way that allows us to adjust different variables like drum speed, in-drum air pressure and more. This helps us 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 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 everytime we roast, it even includes a function that helps us record the inventory of our green beans. Traditionally, roasteries would keep track of roasting processes with just pen and paper, meaning there will be errors and omissions in their roasting profile records. The technology allows us to measure accurately 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.


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 green beans into a heated environment – the roasting drum – so that the water vaporizes. As that happens, the green beans become white, then yellow, then brown.

In the latter stage, something known as the Maillard reaction and caramelization 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 maillard reaction is taking place. This is when the carbonyl groups from sugars and amino groups in proteins react to form aromatic and acidic compounds. Caramelization takes place at 170-200 degrees celsius, and this is when the sucrose in coffee beans browns and dissolves.

As we continue to roast, the beans will expand and crack physically and audibly. We call it the first crack and this takes place at 205 degrees celsius. 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 until a further chemical reaction called pyrolysis to occur -this takes place at 220 degrees celsius and leads to the release of carbon dioxide in the beans.

Why do you offer customers the choice between ‘nutty’ or ‘fruity’? And can you talk us through how you develop each of these blends.

For the two house blends we currently offer, we curated the 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 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 affect the flavour of coffee enormously: if we roast coffee too lightly, the bitter tasting compounds won’t degrade; if we roast coffee batch too darkly, the beans will give the same strong tasting notes of chocolate, nutty and smokey.

The general public still seems to prefer dark-roasted coffees, as they taste stronger and tend 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.