The Art of Roasting
We’ve seen coffee roasting done in domestic ovens, popcorn makers, huge commercial coffee bean roasting machines that need the expertise of a craftsman with years of experience to operate and mega roasters that are fully computer-driven. Interestingly, forty-five seconds either side of ideal will produce a batch of coffee that is either too light in colour if under-roasted (and hence milder than the target roast) or coffee that is too dark in color if over-roasted (and hence stronger or more bitter than the target roast).
Therefore the ideal coffee roaster isn’t going to be an old popcorn maker but to some people’s surprise nor is it the human-operated commercial roaster. It is actually the fully automated roaster that comes out on top as it virtually guarantees consistency. Its computer sensors know with precise accuracy the moisture content, density, average bean size and bean hardness that will all play in part in determining the optimum roasting time. Roasting times will therefore differ from batch to batch.
Generally speaking, the roasting process takes between fourteen and sixteen minutes to complete. During this time the beans expand and they lose weight as water is driven off. The surface temperature of the beans eventually reaches between two hundred and two hundred and twenty degrees Celsius and by this stage the sugars within the coffee beans have caramelised.
The color of the beans changes as they roast. They start off being green then they turn a light brown colour then a chocolate-brown colour and eventually a dark brown color. They will ultimately turn black if left in the roaster for long enough. (Luckily for us as consumers the beans are never roasted this long. As you could imagine, carbon and water do not make a very nice espresso!)
When the desired roast has been achieved the beans are ejected into a cooling tray where they spend about five to ten minutes cooling down to sub forty degrees Celsius. If they don’t cool sufficiently they continue to roast and will retain a very smoky aroma and flavor.
After the beans have settled the oils locked within come to the fore, giving them a “wet” appearance. It is this valuable oil that forms the crema on a well-extracted espresso. All baristas strive to maximise the crema on their coffees as this is from where a lot of the taste and aroma in coffee emanates.
Keeping it Fresh
If given the opportunity the beans will absorb the air and it is the oxygen in the air that will cause the bean to go stale and lose valuable aroma. This is why proper packaging after the beans cool and settle is essential. A high-grade foil bag with a one-way valve is the most appropriate packaging material for coffee beans.For domestic users, coffee should be stored at room temperature in an airtight container
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