Process of roasting coffee
This blog is for coffee lovers, experts and anyone who wants to learn about coffee roasting. I will provide my personal opinion based on my experience, knowledge, and reliable sources of information, for example the SCA (specialty coffee association).
In order to talk about the roasting coffee we need to take into consideration various factors and examine each one. These three factors are our machine, raw material (green coffee), and a program for roasting coffee (Cropster etc.).
Factors
Coffee roasting machine:
The first factor we will discuss is our machine. We should take into consideration what kind of heat our machine uses, gas or air. Based on this we need to take into account what kinds of heat we can use; radiation, convection and conduction. In many cases we will use all three or only two. We should always take into account our connection to the heat sources and calibrate our machine accordingly.
Raw material (Green Coffee):
The second factor to take into account is our raw material or our green coffee. We need to know various factors that can affect our roasting process.
What variety is our coffee? What process of fermentation does our coffee have? What is the humidity of the grain? What is the water activity (AWU)? What is the density of the grain? How much quantity will we be roasting?
We will need to respond to each of these questions. When looking at the varieties of coffee, the most common is Arabica family. For example, here in the Quindío region of Colombia at our farm, Finca El Ocaso, we have cultivated varieties of Arabica such as, Castillo, Tabi, Geisha, and Pink Bourbon. We process our coffee with various fermentations such as natural, honey, anaerobic and prolonged fermentations. These processes give us a very important starting point to define our roasting curve. After processing our coffee, it will be ready as green coffee and we can make our humidity analysis, density, and water activity. Lastly, we need to choose the quantity of coffee we are going to roast in relation to the capacity of our machine. Keeping in mind that the quantity of coffee should not go beyond 70% of the capacity of the machine.
Cropster for coffee roasting:
Finally, discussing our roasting coffee program, here in our farm, Fincal El Ocaso, we use Cropster. This is the most exact tool for reading the curve, it has many options like green coffee inventory and the ability to cup the samples with a score. Another benefit of this program is the possibility to save the roasting curve and replicate it. Cropster is an excellent program for its precision in the reading of the curve during the roasting process. It also has the capacity to identify the dehydration, change of color, first crack, and caramelization during the roast. We will talk about this more in depth in the next example.
Coffee roasting Example :
The idea is to roast Geisha variety coffee with the fermentation process of honey for 120 hours. Our machine is a national brand of 10 kilograms and works with gas. So, for this example we will roast 8 kilograms of coffee. First, we need to measure the humidity, which should be in the range of 10-12 percent. If our coffee is low in humidity we won´t be able to use a lot of heat during our roast and if it is high in humidity we will have to use more heat than normal.
The next step will be to measure the activity of water; this step is not necessarily mandatory. Now that we know our range of humidity we will know if the activity of water will be in the appropriate range between 0.65 and 0.66. This measurement is simply to keep in mind how much time our coffee has been in the warehouse and if there is embryo life inside the bean.
Lastly, in our measurements we need to keep in mind the density of coffee. The easiest way to calculate the density of the coffee is to weigh 50 grams of raw material and put that into a graduated cylinder. In order to get the density you divide the quantity of coffee in the graduated cylinder by 100. A density between 0.65 and 0.67 means that it is a coffee with a low density, so when it is time to roast we cannot use a lot of heat with this low density coffee. On the other hand, a coffee that has a density higher than 0.67 is considered a high density coffee and we will need to use more heat to roast.
Now that we know all the measurements of our raw material, we have to choose what temperature we will start our roasting process at. It is very important to keep in mind the quantity of coffee we are going to roast. In this case, I chose a temperature of 180 Celsius. This temperature is appropriate for the quantity of coffee we are going to roast because it is not too hot and not too cold according to the measurements we made. The more experience and practice you have will help show you the best temperature to start your roast. After this we will start our roast and this will be divided into four steps.
Step 1:
Dehydration. Starting from the moment that the curve begins, the internal temperature of the machine will start to fall until it finds a turning point. This point is between 90 and 120 Celsius depending on the type of machine. From this point on, the coffee will start a process of dehydration, evaporating water and lowering humidity continuously until it starts to change color. During this process of dehydration, we will smell something similar to dry grass or vegetables. If we make the dehydration process longer, we can achieve a sweeter coffee. And if we make it shorter, we will have a more acidic coffee.
Step 2:
Change in color. This is the moment during the roasting process where the Maillard reaction will begin. The majority of the physical and chemical changes occur during this reaction. The Chlorogenic Acid changes gradually forming volatile aromas, quinine and caffeic acids. The sucrose also changes forming volatile aromas and caramels giving the first color of roasted coffee. In this point we will be at a temperature between 140-160 Celsius.
Step 3:
First crack. The heat inside of the bean generates an explosion similar to that of popcorn. The first crack is the beginning of our internal development of the bean. It is the point where we should be the most concentrated because it is the lowest point of humidity and density during the roast. This makes the coffee roast very quickly during this step. The first crack helps to develop the roasting process of the internal part of the bean starting the caramelization process within. Our Cropster software during the entire roasting process, will be controlling each of the variables and marking a line in each of these steps controlling the time, temperature of the grain and the machine, and the rate of rise (the increase of temperature minute by minute). In the future in another post, we will examine the rate of rise in a deeper context.
Step 4:
Development. The development begins in the exact moment when our Cropster software marks the first crack. This will be the time when we will give the final touch to our coffee, choosing a low, medium or high roast. For this, our Cropster software will indicate for us the exact development in a percentage during this step. For our Geisha, we have decided to give a development of 18% one minute forty-five seconds after the first crack. We will give our Geisha a medium roast and this percentage of development will permit us to highlight floral notes, caramel, medium body, and a brilliant acidity. This will give us a medium roast to be used for filters or espresso. Lastly, to find our roasting point of our coffee we will take it out quickly and start the cooling process. This prevents the coffee from continuing to roast.
Finally, we will cup our coffee and we will give it a profile and score. This coffee is one of the coffees with the highest scoresf at the Finca El Ocaso. Thank you for reading, I hope you learned a lot about my passion and I look forward to learning more about coffee together in another post.
You can buy coffee at Finca El Ocaso ,the best coffee for me is passion 300 and natural process.Visit us!!
Santiago Patiño Cadena
Roast Master From FInca El Ocaso.
Regional Roaster Championship.
2nd Place National Roaster Championship.
