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Last week we had a look at the basics of coffee. Today we are going to go a little more in depth on one of the most important phases coffee beans take on their trip to your cupboard - roasting. How coffee beans are roasted has a very big impact on the final taste profile of your morning cup of java. So what should we look out for when we're stood pondering our purchase in the shop?

On a commercial scale, roasting predominantly occurs through either drum or hot-air roasting. The first uses a large horizontal drum with coffee inside, that is rotated to ensure heat is spread evenly from a heat source underneath. The hot air method uses large mesh beds with the coffee placed on top heated by, well, hot air, from underneath with enough pressure to lift the beans and allow them to mix and spread the heat.

Depending on the desired roast, a combination of time and temperature will be monitored, although other cues such as sight and sound can also help roasters to hit their target. As they roast, coffee beans change through darker shades of brown and eventually black if you're not careful (or like things well done!) The sound is a handy indicator, as beans make a very audible crack at two points as they heat up. There are many different stages of roast which we will now handily beguile you with in bullet point form:

-Unroasted- Starting off green, coffee beans will turn yellow as they begin to roast and moisture evaporates.

-Light roast- Hovering at around 200°C, light roasts occur immediately as you hear the first crack. At this stage, the beans haven't had long to caramelize, so the taste isn't very sweet and has higher levels of acidity compared to darker roasts. The origin taste is strong, the characteristics decided by where and how the bean has grown.

-Medium roast- Moving up into the teens, medium roasts start to see acidity drop off and the flavour of the roast has more of a bearing, though the origin still comes through.

-Dark roast- As the temperature reaches the 220's and 30's, the second crack is underway. Caramelization lends a bittersweet taste as the acidity drops off and the roasted taste becomes very prominent, with the origin overpowered. By the 240's, the roasted taste turns into a burnt one, with little to no acidity. Turn back now!

Although it might seem odd, you could always have a go at roasting your own coffee at home. At one point it was the norm, but as commercial roasting companies took off in the 20th century it's a practice that largely fell by the wayside. Today it's seen as more of a hobby, though it's a great way to experiment with your favourite drink and even save a bit of cash!

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