Coffee Roasting & Harvesting | Techniques for Flavour

Whether it's plunged, percolated, or poured over, the flavours you taste in your cup of coffee are steeped in the stories from its plantation to its packaging. The way coffee is processed from harvest to roasting has more to do with the final flavour than you may think.

I think it’s fair to say a lot of us coffee drinkers probably consider ourselves aficionados when it comes to what we know about our morning brew. But, despite many of us being happy to snobbishly write off an average coffee as down to the barista, chances are you’ve never thought to ask the questions on what really makes that coffee taste the way it does. 

We interviewed coffee roaster Thomas Enright of Leftfield Coffee Roasters to get the good word on the ins and outs of what to consider when sourcing and roasting. 

Ollie: Firstly, thanks for joining us, Thomas! Diving straight in, in terms of the roasting process itself, are there certain stages of the roast to consider when trying to achieve certain flavours? 

Tom: No worries, Ollie. I'm happy to answer a few questions! There are multiple stages during the coffee beans’ time in the roaster, and each phase needs to be treated differently by the roaster in order to get the best-tasting coffee possible.

The first ‘drying’ phase begins when you drop the bean into the roaster and ends when the beans turn a yellow colour. During this phase, the beans are endothermic, absorbing heat at a very high rate. Inside the coffee bean, water, chlorogenic acids and trigonelline are decomposing. The transformation of water into steam causes internal pressure to build up inside the bean which causes the bean to increase in size. Before they roast, beans are actually far smaller.

In the second ‘browning’ phase, the coffee has developed a significant amount of thermal inertia and goes through a chemical process known as “Maillard reaction”. This reaction refers to the reduction in simple sugars and amino acids, causing the formation of melanoidins. Melanoidins are responsible for the coffee’s change in colour. This is the same reaction as when you put bread into a toaster. Delicious aromatic compounds are a by-product of this phase. The end of the browning phase is signalled by a loud crack of the coffee beans. This is called the “first crack”.

The third ‘caramelisation’, or ‘development’ phase, occurs when beans have released most of the pressure built up inside, releasing heat to produce the caramelisation or development of sugars. This phase is significant in creating the appropriate flavour that the roaster aims for. Simply put, the shorter the development time, the more vegetal or sour flavours are present. The longer the development time, the more sweetness and bitter flavours you will get.  Some of our more traditional roasts go to a point called ‘second crack’. Not many roasters try to do this because it’s a very fine line between being delicious and too harsh. 

Ollie: It sounds like it depends a lot on the styles that a roaster wants to achieve. What are some of the main styles we would be likely to see? 

Tom: A roaster or barista’s idea on how they want to create flavour or drink their beverage usually changes over time. In relation to coffee, there aren’t branded names for styles of coffee roasting, but I’ll do my best to categorise the three main ‘styles’.

First, we have traditional Dark Roast. The colour of a Dark Roast can vary from that of a milk/dark chocolate blend, all the way through to borderline black (this is typical of your very old-school Italian-style roasts). These roasts expose the bean to very high temperatures, and if done in a certain way, these roasts will generally have a sweetness of rich, caramelised sugars (heavy caramel, toffee, molasses, dark chocolate notes) with no acidity. More traditional, old-school Italian-style roasts even tend to contain a burnt or ashy taste.

Secondly, we have the more modern Medium Roasts. The colour of these roasts looks like milk chocolate or a rich mahogany/wood. Medium roasts are exposed to lower temperatures than dark roasts, so common flavours associated contain a sweetness of caramel, sugarcane, butter, pastry and milk chocolate. These roasts will have will have preserved some acidity in the bean that may taste similar to that of some fruits. There will be no toasty aftertaste and very little bitterness if brewed correctly.

Lastly, we have the modern Light Roasts. These have a colour similar to light or standard milk chocolate. These roasts are exposed to far less temperature and time within the roaster. This preserves a lot more moisture, with common flavours holding sweetness similar to that of most fruits such as apple, stone fruits, or melons. If brewed correctly, you will taste a lot more acidity and less body than any of the other roasting styles. If roasted too lightly, however, these roasts can convey notes of sourness or other vegetal notes.

Courtesy of Leftfield Coffee Roasters

Ollie: It sounds like it really comes down to preference, but what about roasting methods? How do manual methods stack up against automated roasting methods?

Tom:  A lot of people think you just put the bean in the oven, watch it go brown, then cool it down, but there is so much more science and engineering involved than that.

Automated roasting machines allow coffee roasters to develop a set way the bean needs to be cooked based on what style or flavour that roaster wants to get out of a specific coffee bean. The roaster will then translate desired roasting factors into profiling software, which is then connected to the roasting machine, and all you need to do is press play and watch it roast. There is nothing as accurate as computers and technology (not even humans, unfortunately). This style of automation also makes the process of roasting and data collection a lot easier on the roaster when it comes to analysing each roast profile and making adjustments.

Manual roasting techniques are only similar to automation in that you still need to develop a particular roasting ‘profile’. Manual roasting is done by simply writing down the steps on how to achieve that profile on a piece of paper and using that piece of paper as a guideline. Essentially, it comes entirely down to the roaster. There is no technology directing you, altering the airflow of the roaster, and no sign on a computer giving you a signal when to change the heat source. The increased concentration and attention to detail required forces a heightened sensory experience through every roast. From the smell and colour, right down to the temperature of the air on your skin, roasting manually helps us notice even the most minimal changes that computers don’t always show.

Courtesy of Leftfield Coffee Roasters

Ollie: A lot of people also tend to have an opinion about which country has the ‘best’ coffee beans. Is there any truth behind the geographical origins and the flavour of the beans?

Tom: Definitely, but it’s important to know that the vast majority of coffee is actually compiled into a mixture of multiple different origins based on the different flavours from each different country. 

We desire Brazilian coffees that are very balanced and have tones of caramel with nut-butter-like sweetness and a large body. South and Central American coffee may ooze in delicate chocolate, buttery/pastry notes with a diverse range of bodies depending on where you go. African coffees are known for their fruity, winey and complex flavours. India and Indonesia are known to grow very distinct coffees that reveal an earthy, full body with a luscious and syrupy sweetness.

Ollie:  What about the harvesting process? Would different harvesting techniques have any real impact on what flavours the beans are able to produce? 

Tom: Coffee harvesting plays a massive role in coffee's flavour. 

The oldest is the natural processing method. Here, after picking the whole coffee cherries with fruit included, they are placed onto a raised bed or mat to dry. These cherries are turned/raked regularly to ensure no moulding, fermentation, or rotting takes place. Once dry, the outer skin and inner parchment of the cherry are taken off mechanically, and you’re left with two seeds. The bean in this process absorbs the essences and sugars of the fruit's drying flesh. In the cup, this translates into a fruity or boozy-like quality.

Washed processing, on the other hand, aims to remove all of the flesh from the coffee seed before it is dried. It involves sending the picked cherry through a pulping machine. This takes off the outer skin whilst leaving the inner pulp (known as the mucilage). The pulp-covered seed is then sent to a bed of water, where the flesh is removed by fermentation and agitation. The coffee is then washed again and dried on raised beds or mats. This gives much cleaner and crisper-tasting coffee.

A few coffee-producing countries have developed idiosyncratic processing methods that have come to define the country/region's flavour profile. Brazil, for instance, is known for its ‘pulped natural process’. After picking, the coffee is mechanically de-pulped and dried with some flesh still surrounding the bean. Some Central American producers use ‘honey processing’, similar to the pulped natural process, but it requires less water and the de-pulping machine can be controlled to leave a specific amount of flesh on the seed before drying. Indonesia is home to a process called Giling Basah or ‘wet-hulled process’. After picking, the coffee is de-pulped and then only briefly dried, leaving significant moisture within the bean - contributing to Indonesia’s typical earthiness, body and low acidity. It is then sent for hulling, where the parchment is ripped off, and the exposed bean is sent to dry.

Larger-scale coffee producers now have access to more technology, allowing for a lot of experimentation to occur, especially during the fermentation phase. Producers are currently experimenting with techniques such as carbonic maceration, a fermentation technique used in the wine industry. Some producers are experimenting with triple fermentations as well as using specific yeast compounds to enhance reactions that boost certain flavour profiles that can make a coffee taste more like fruit juice…. It’s getting pretty crazy.

Ollie: Lastly, where do you see the future of sourcing, roasting, and drinking coffee heading? Many industries are angling towards more ‘green’ practices, with sustainability becoming a key priority for producers and consumers. Is this the case with coffee? 

Tom: Coffee is prone to the same climate change related problems that all agricultural industries face. According to a study conducted by World Coffee Research (WCR) in 2017, the ideal temperature for Arabica coffee to grow in producing origins ranges between 18-21°C. It is forecasted that by 2050, average temperatures in these regions will be as high as 32°C. This poses a risk to farmers and their ability to produce a significant enough yield to last them until the next harvest. Because of this factor alone, there is now research being conducted by WCR on developing genetically engineered varieties of coffee that will be able to grow in these warmer and ‘traditionally undesirable’ conditions in order to maintain coffee production.