How We Roast Coffee

How We Roast Coffee

In my role as head roaster, I want to respect the amazing green coffees Tim sources, and all the hard work the farmers, producers, exporters and importers have put in to get the coffee to us. It’s my job to unlock the potential in each coffee and get it to taste the very best I can.

In its natural state, the coffee bean is flavourless. It’s only by applying the right amount of heat, for the right amount of time to green (raw) coffee that we’re able to bring out the incredible array of flavours and aromas you can taste and smell when enjoying a cup of our coffee.

A coffee will roast differently depending on its origin, varietal, processing method, age, density...the list goes on! So whilst we have certain parameters of how we roast, each coffee will behave uniquely when it’s in the roaster.

Profiling coffees

To make sure our coffee tastes the very best possible, every time we start roasting a new coffee, we’ll profile it a number of times, playing around with variables such as end temperature, length of roast, and development time (the length of time after ‘first crack*’).

Next we cup, or taste, these profile roasts, and decide which roast brings out the best in that particular coffee. We’ll then lock it into our roasting software – Cropster – and start roasting! Every now and again we can be surprised at what tastes best, so it’s vital we profile our coffees a few different ways. We’ll regularly taste production roasts to make sure we’re happy with them, sometimes tweaking profiles if we think we can improve the flavour.

*First crack is when the heat builds up enough in the bean that it literally cracks (a bit like popcorn!).

Our roaster

At our roastery in Essex, we use a 5kg Probat cast iron drum roaster. Roasting single origin coffees in small batches to bring out the best from each process (natural, washed or honey), varietal (e.g. Catuai, Caturra, Bourbon) and origin (Central and South America, Africa, China).

Drum roasters rely mainly on conductive heat – the transfer of heat from the drum to the beans – to roast coffee. There’s also a certain amount of convective heat from the hot air circulating in the drum. We can play around with this convective heat using our adjustable air flow damper.

Our roaster has multiple temperature probes that measure the bean temperature inside the roasting drum, and the exhaust temperature exiting the drum. We use software called Cropster which is hooked up to the roaster, and these temperature probes to control the flow of heat and air.

Cropster records all our roasts on time vs temperature graphs. This is essential for profiling new coffees, and also production roasts when we want to repeat the same roast again and again. Cropster also stores all our green coffee stock, and is an indispensable library and evaluation tool of all the roasts we’ve ever done on our Probat!

Roasting for espresso vs filter

All our coffees are roasted with care so that they don’t lose their inherent delicate flavours and aromas (you might have heard of ‘light’ and ‘medium’ roasts). By roasting a coffee for too long, or with too high temperatures, these delicious aspects can be lost, and replaced with the bitterness most people assume is inherent in coffee.

However, for espresso roasting we want an end product that cuts through milky drinks and is easy to work with for our wholesale customers. By developing a coffee more, we can also increase its solubility which can be helpful for espresso brewing.

With our filter coffees – ones that are more suited to pour over brews, for example – we might use a little less heat and time to retain more of that coffee’s delicate character.

Now you have a bit more of an idea what goes into producing the delicious Wood St Coffees you enjoy, head over to the shop to take a look at our current selection.