Coffee information from The Coffee Brew.

Roasting Coffee Beans…..what happens during processing?

Now that you have some idea from our previous article about the basics of roasting coffee beans at home here is some more information on how to achieve a good roast. First of all you have to start with good quality beans that have been expertly selected and dried.

What happens is some bean processors use a wash to remove the fleshy fruit from the bean and to separate different kinds of beans in the batch. As there is density differences in the beans this will cause some of them to float higher. This makes removal or separation much easier. There is also a dry process used by some processors but this is slower and more expensive.

It is interesting to note the two processes produce different results – the dry processed beans have a more subtle acid taste whereas the acidity of wet processed beans is more striking. It is desirable to have some acidity in your coffee….if not you will end up with a pretty flat and tasteless cup of brew.

So what does happen to beans as the temperature rises during roasting?

Through the roasting process aromatics and acids plus other flavor compounds are produced in varying levels of concentration.

In the initial stage the beans absorb heat and these green beans are slowly dried to a yellowish tinge. What people refer to as green beans is not necessarily the color – it simply means the beans are not yet roasted or – in other words they are raw beans. When properly roasted, the beans will have an aroma similar to toast or popcorn.

Here’s one reason why coffee beans must have the correct moisture content – which comes from the drying process. From about 170°C-200°C (338°F-392°F) sugars in the bean will begin to caramelize aided by the increase in temperature of the moisture enclosed by the outer skin. Caramelized sugars are less sweet, so reaching the ideal water content is important for the flavour of the final brew.

As things in the kitchen get hotter a few more things start to happen. At about 205°C (400°F) the beans will expand to about double their original size and become light brown in color while at the same time losing about 5% of their original weight. As the temperature rises to about 220°C (428°F) the beans will lose about 13% more weight and release some CO2.

Now applying a bit more heat to around 230°C (446°F) the roasting beans start turning medium-dark brown and take on an oily sheen. More than often there will be a loud pop as the beans enter their 'second crack' phase.

This is the stage where you, as a budding coffee roaster, have to be a little bit cautious and not overdo the roasting. Right around now volatile aromatic compounds are boiled off and the oils on the outside of the bean can combine with oxygen in the air. That process can strip the bean of its unique flavors resulting in a burnt taste – not the gourmet type of experience you were really looking for.

For a great cup of coffee the aim is to arrive at just the right balance of bitterness, acidity and a whole heap of other little attributes. All this (plus a little bit of practice) will determine the final flavor of your next brew.

What does the term ‘body’ mean? In coffee that is!!

You have probably seen coffee connoisseurs using this reference in tasting guides as if we all know what they are talking about. Well despite what ‘body’ suggests it doesn’t refer to the actual thickness or viscosity of the beverage. That particular attribute is the result of the kinds of proteins and fibres in the brew.

To coffee tasters, body refers to the feel on the tongue when it is rubbed on the roof of the mouth. It's the result of the fat content in the drink and that, apart from the plantation growing conditions, is something home roasters can't control. It is pretty much determined by the roasting process.

Just a couple more quick tips before we finish. If your roast is too light it will leave too high a concentration of bitter compounds in the final product. On the other hand, if it is too dark then you will produce an excessively chocolaty, burnt taste.

Coffee roasting is all about experimenting to find the perfect taste for you. There are heaps of good coffee roasters available on the market today so now you can turn your interest into a total gourmet experience where you can both produce and enjoy your very own unique specialty blends.


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