Everything you wanted to know about coffee roasting and grinding
Roasting is an indispensable part of what turns freshly picked green coffee beans into the aromatic
cup of life-giving goodness that we know and love. The roasting process gives coffee its characteristic flavour and has been carried out since the 15th century.
With an aroma akin to freshly cut grass, green beans don’t smell like coffee at all. Heat is used to
transform these fresh nuggets into brown beans and different roasting methods can affect the
flavour of the end coffee product. When coffee beans are roasted, 800 to 1,000 different aromatic
compounds can be developed to determine the flavour of the resulting cup of coffee.
Coffee roasting process
The roasting process usually consists of three main stages: drying, browning and the development or roasting stage. Because the beans can contain as much as 12% humidity, they need to be dried before any actual roasting can take place. Drying usually takes from four to eight minutes and it is vital that the beans do not burn. With final drying temperatures reaching 160°C, this is when the aroma of the coffee starts to become recognisable. During the browning stage, something called the Maillard reaction takes place, promoting the production of melanoids that give coffee its typical
flavour and colour. They’re also crucial in producing and stabilising the smooth crema on top of your espresso. Shortly after the Maillard reaction is when caramelisation occurs, but if this is allowed to go on too long, there’s a risk that bitterness may start to creep in.
The final stage is the roasting itself, when the aroma compounds properly develop. The desired flavour profile is created simply by tasting or through the use of a colour metre. A range of other factors can also be taken into account, including the origin of the beans, variety, moisture content, density and processing method. The key aim of profiling is usually to enhance the flavour of the coffee beans in question rather than trying to create something from scratch.
Coffee first and second cracks
During the coffee process, roasters listen out for two loud “popcorn-like” cracks, cleverly known as the first and second cracks. The first takes place at approximately 196°C, marking the start of a very
light roast. Much of the coffee’s moisture has now been evaporated and the beans will begin to swell. At 224°C the second crack occurs, indicating that the coffee bean is starting to fracture due to
internal pressure. This usually signals the need to end the roast, if it hasn’t ended already. These reactions can be very hard to anticipate, hence the skill involved.
Long and short coffee roasting
Coffee beans can be roasted in different ways depending on the type of coffee they’re destined to become. There are three roasting levels: light, medium and dark. Traditionally, espresso is best made using dark roasted coffee, also known as Italian roasting, high bitterness and is big on the body. The brown of the beans is dark, almost black, and the oils are clearly visible on the surface.
Bitterness is the main characteristic of this coffee, making all other traits vanish during the phase which follows the second crack. In the Italian tradition, it is considered the most suitable roasting for espresso extraction, even if this myth has now been dispelled.
The degree of roasting is generally lighter for filter coffee than espresso, with less acidity. Medium roasts tend to taste smoother and more traditional in the cup. Light roast coffee is popular with specialists for its ability to bring out more unique flavours. One thing worth remembering is that weight on weight, the level of caffeine is pretty much the same regardless of the degree to which the beans have been roasted.
Coffee roasting at home
Coffee is usually roasted close to its site of consumption as green coffee is more stable and easier to transport than the roasted beans. Although most beans are roasted industrially, some coffee connoisseurs prefer to roast at home as it allows them to experiment with different flavour profiles and ensures maximum freshness. Coffee stays at its most flavourful for a week after roasting.
Roasting at home can also be cheaper than buying pre-roasted beans and gives you the chance to experiment with different coffee origins to find your favourite brew.
Coffee grinding: how does it work
Once the beans have been roasted, the next very important step is to grind them into usable coffee. Even a simple understanding of the best way to grind coffee can seriously enhance your cup. Freshness is key – your coffee will immediately begin to lose freshness as soon as it comes into contact with the air.
Coffee can be ground into different sizes and it’s important to pick the right size for the brewing method you intend to use and the length of time the coffee will be in contact with the water. If you’re planning on using a French press or cafetière, a coarse ground coffee is the best option as it will sit in the water for a prolonged period. For an espresso machine, when the coffee can be in contact with the water for as little as 30 seconds, a fine grind will help you achieve that sweet taste. If the grind is too coarse, that full-bodied coffee flavour will be at a minimum. Generally speaking, if your coffee tastes too bitter or even sour, try a finer grind to fully max out on flavour.