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similar to fast roast, but it’ll be less acidic but sweeter. This is
the answer to why coffee beans with similar colour have differ- 3 Must-dos for roasters
ent taste.
1. Weigh the beans
Slow Roast Weigh all the beans you want to roast to de-
If we are roasting for Italians who does not like acid- termine the starting charge temperature and the weight
ity, reduce the heat after the first crack at 8th minute and roast lost. Coffee beans lose 15% - 20% of weight after roast-
until 11 minute 25 second. We should have the finishing roast ing. To calculate the loss, use the following formula.
temperature at 210 °C and the development time of 3 minute ; L= Loss, G = Green beans weight, R = Roasted
25 second. The result should be a mildly sweet and bitter coffee beans weight Example: 5 kg of green beans give 4.2 kg
with thicker body and no acidity.
All 3 kind of coffee beans have similar colour and it’s of roasted beans, then the loss equals
near impossible to determine their taste just by looking. If we 0.16 or 16%. If the loss is too high, it might point to some
continue to roast after slow roast, the coffee will get more bitter problems like excessive roasting temperature or the
and burn. moisture content is off. Since coffee is sold by weight,
weight loss is an important subject to consider every
time you roast.

2. Measure the Moisture Content
Use a Moisture Meter to determine the mois-
ture content of the beans you want to roast. Arabica
beans should have the moisture content between 11-12%
and robusta beans should have the moisture content
around 13%.
Moisture content affects coffee flavour and
the time to reach the first crack, which in turns affect
caramelization and flavour development phases. It’s all
connected!

3. Measure the beans density (Bulk Density Testing)
Flavour Emphasis by Roast Degree You’ll need a graduated cylinder to determine
the density of the beans as denser beans require higher
temperature.

The example shows how important flavour develop-
ment is. It’s essential to pay attention to the time and tem- Fill the cylinder with the beans to measure the
perature after the first crack in order to control the flavour, volume and weigh the beans. Use the following
especially if we are roasting specialty coffee. For example, if we formula to determine the density.
want to highlight the acidity of a Geisha and we use slow roast
approach, the coffee will lose the acidity and it’ll be a waste of
good coffee. *** If possible, Green Bean Grading and Screen
Roaster experience is critical as you need to know Size Check are another 2 steps you could do before
the beans you are roasting. What variety is it? How was it roasting.
processed? How dense is it? What is its moisture content? You
need to understand the beans for you to bring out its desired
character.
For instance, Kenyan coffee is denser and it requires
higher finishing temperature. Normally we want to bring out
the chocolate and floral character of Kenyan beans out with a
little acidity, so an ideal roast with 2 minute 20 second devel-
opment time would be the approach. The result would be a
balance roast with balanced acidity, sweetness, and bitterness.
Sometimes customers ask for an impossible roast, for CTI would like to thank Mr. Sarawut Premchit (Woody)
example, a very acidic coffee with body. But according to the from Intercof Co., Ltd., and we hope the reader will find
graph, body builds up as acidity decreases. this article useful. For more coffee roasting information
and technique, follow Woody’s facebook page, “Thai
Roaster Club” or enroll in Intercof’s Special Roasting
Course at www.coffeeteach.com.