What affects coffee during roasting
Controlling variables during roasting process
Coffee roasting includes adjusting many variables to create your perfect roast profile. By changing factors including temperature, length of roast, and airflow, you can highlight sweetness, emphasize acidity, or create a well-balanced roast. also drum speed, you can affect the amount of time that coffee beans are exposed to direct heat.Now you can change all those variable, Should you roast a Colombian Nariño the same way you would an Ethiopian Sidamo? Probably not.Producing countries have different climates, soil types, altitudes, density, moisture, – and all that leads to very different coffees. The beans will react differently to heat, plus you will want to accentuate specific characteristics. In other words, you need to roast them differently.So before you create a profile and put your coffee in the roaster, you need as much information as possible about the beans. And today, I’m going to take you through some of the main origin-based variables to consider. At each stage of the coffee supply chain, the moisture content of a green bean must diminish – or the bean might become moldy, defective, and less valuable than before. Ensuring a bean dries correctly is essential in order to optimize its quality potential and minimize the chance of problems.Roasters, near the end of the supply chain, have two tasks when it comes to managing moisture content. On the one hand, they must maintain the lots they store onsite within a narrow moisture range that is acceptable to their quality standards.
On the other hand, and in the span of a few minutes, the roaster is responsible for driving the last remaining bits of moisture out of the bean via the application of intense heat and pressure. In these minutes, the coffee is exposed to the most energy it will experience at any point in the coffee supply chain and the roast is set up for either success or failure.It’s easy to see why roasters should care about the moisture content of their coffee. But how useful is a number supplied by an importer, and how can roasters integrate moisture content readings into their craft? I spoke with Fred Seeber of Shore Measuring Systems, a supplier of moisture content meters, about measuring and making sense of moisture content in green coffee.
There is no official standard for ideal moisture content in green coffee, although the ICO recommends 11% as a good target. However, it’s commonly accepted that 10-12% is a reasonable range. Anything less than 10% is likely to result in loss of cup quality, while humidity at higher levels begins to create a risk of mold growth. Yet a coffee’s humidity is not static. While the pre-export drying process drastically increases a bean’s stability, changes in moisture content are still possible. Environmental factors, such as being in a particularly humid or hot location, are a common cause of this. Before getting into the technical details of measuring moisture content, it’s worth digging a little deeper into why it’s worth measuring moisture content. Knowing this will help you establish protocols suited to your specific needs.
For roasters of a certain scale, it’s simple: you pay for coffee by weight; the more water in that coffee, the more you’ve paid for water which you’re going to burn off anyway. common situation roasters find themselves in: “So, [an importer] sends you a sample, and… it’s showing 11.5% moisture in that sample. Then when your container shows up, that’s 40,000 pounds, and all of the sudden you discover it could be 13% moisture. Well, you just got blanked for two percentage points of water of a commodity that’s four bucks a pound… that’s [a lot] of money.” For the smaller, quality-focused roaster, those kinds of calculations may or may not be relevant. But moisture content still plays an indirect role in a roaster’s costs, regardless of whether or not they’re buying a few containers or a few bags.
There is no direct link between a coffee’s quality and its moisture content. A 10% humidity coffee is not necessarily better or worse than a 12% coffee. However, over time, green coffee will gradually lose vibrance. This will eventually result in the dreaded “past crop” flavor, and this process is associated with the drying out of the coffee. Therefore, even for a small roaster, it’s important to keep track of moisture content. If you paid for an 85-point coffee at 12% moisture, by the time it reaches 10% moisture it may be more like an 83-point coffee. Yet, you still paid 85-point prices for it originally.
By comparing moisture content loss with quality degradation over time, you can make smart buying and consumption decisions with your green lots. And, when combined with water activity measurements, you can even predict the shelf life of your green coffee. Again, precision here is key: you want to track your coffee through a narrow range of percentage points over a long time frame. Lastly, you may think to yourself that you don’t need to measure moisture content yourself, since your importer supplies those numbers already. Fred cautions against this thinking. He points out that coffee is shipped on water and that ports can often be warm and humid, which will affect moisture readings. So, if you’re a roaster in a dry part of the United States but your importer is located in New Orleans or Houston, and is taking moisture readings from lots right as they arrive, those numbers might not be applicable to you by the time your coffee arrives at your facility. Elevation, or altitude, is of immense importance for coffee roasting – but what we’re really talking about is density. When coffee is grown at cooler temperatures (which, most of the time, means higher elevation), the cherries ripen slower and so develop more sugars. This leads to more complex sweetness, but also to harder, denser beans. When you have beans of different densities, they also react differently to the heat. Soft, low-density beans tend to have more air pockets inside them, which can slow down heat transference. To avoid scorching the outsides of the beans, you should use a lower initial charge temperature. We also recommends extending the length of the roast for these coffees. Knowing what altitude your coffee is grown at, how far it is from the equator, and the temperature on the farm will help you to anticipate the density. When roasting, it’s important to consider not just the structure of the bean, but also the flavor of it. And this can vary greatly. “We will never have an Ethiopian with the same type of acidity like that Kenya AA Kamwangi we once had,” Tom tells me, “and it will be very difficult to find a Colombia with the stone fruit, tea-like flavors of the Yirgacheffe coffees.”
you can expect well-balanced coffees from the Americas, with more chocolate and hazelnut notes appearing in Brazil. In East Africa, coffees tend to be clean, juicy, and fruity. Some regions lean more towards sweetness (like Burundi), while others are more acidic (like Kenya). Indonesia is often known for its heavy body and earthy tones. Yet there are so many flavor variations within one region, as a result of micro climates, terroir, varieties, production and processing methods, and more. Sulawesi, Indonesia is famous for its spice notes, while Bali has a more citric profile. A Panamanian Geisha will taste different from a Panamanian Bourbon. Brazil is so large, you can fit much of Europe in it – and it has a wide variety of profiles to match. And as Tom points out, some countries have multiple harvest seasons. it’s the roaster’s job to preserve what makes an origin special and “let the coffee speak”. Knowing the profile of the coffee origin will help you anticipate which flavors will be most prominent – and how you can emphasize them. roast graph data into two types of curves: control curves and reading curves. Control curves are variables that you directly control during the roast, such as the heat settings, airflow, and gas flow. Reading curves are temperature readings. Since the variables are constantly changing, they are recorded as line graphs.
But what reading curves do you need to know? the key ones are bean temperature, air/environment temperature, and rate of rise curves – although you can also measure bean color, air, and gas pressure for even greater insights. Denser, higher-altitude coffees are associated with greater acidity, and you’ll often hear this described in terms of fruit notes – mandarin, grapefruit, plum, blueberry, and so on. This is a highly prized trait, and if you’re roasting a coffee that has this quality, you may want to accentuate it. (Bear in mind, however, that while acidity can be good, underdeveloped and sour notes are not. There is a fine line.) the more acidity and fruitiness you will throw away. A faster Rate of Rise (RoR) is also recommended by many roasters for emphasizing acidity. On the other hand, if you want more sweetness – say you have a natural Bourbon from Burundi – then Willem Boot, CEO of Boot Coffee, recommends opting for a lower RoR. Sweet Maria’s also experimented with stretching out the drying phase of the roast, and found that it could highlight this quality. as for body, stretching out first crack could open up a more syrupy mouthfeel in a coffee. It’s important to remember that the qualities you want to highlight will all depend on the coffee itself, and its unique, overall profile. Roasting is a complex skill; there are no simple rules. These guidelines are just starting points for creating your roast profiles. Knowing the altitude, temperature, terroir, and origin profile is a great start to creating a roast profile for a coffee. “It’s about a commitment to get to know the origin and bring the best to the surface,”
But it’s only a start.
Bean temperature(the blue line)
The bean temperature curve will look a bit like a check mark; once it starts going up (something called the turning point – more on that to come!) it should always continue going up. If not, you risk stalling your coffee and developing bread-like, doughy flavours
ROR(other blue line which is vice vers)
The rate of rise curve is linked to bean temperature, but there’s a subtle difference: it measures the rate at which bean temperature changes. This will give you far earlier indications of temperature changes and, in turn, allow you more control over the roast. It has a very different shape to the bean temperature curve, rising sharply from zero shortly after the turning point.
Air temperature(RED line)
Air temperature is variable measures the environment inside the drum. It’s useful to know because much of the heat transfer in coffee roasting is via air. This line will follow a similar shape to the bean temperature curve.
Key Stages on Your Roast Graph
Now we know what the roast graph measures, you can start reading and interpreting these lines. To do so, you want to pay attention to several key points on the graph: charge temp, turning point, first crack, and end temp.
This is the temperature of your drum just before you add the coffee. By manipulating this, you can speed up or slow down the rate of rise and, in turn, choose how much acidity to accentuate. You should also pay attention to bean density and processing method when selecting this.
As you add the cold beans to the roaster, the heat inside the machine will dramatically fall before starting to rise again. The point at which it begins to rise is called turning point.
One of coffee roasting most famous moments is first crack. First crack signals that the beans are almost ready. As the beans expand and moisture evaporates, steam develops inside the beans. This steam then forms pressure that cracks the beans open.
First crack it’s a moment that has been given almost mythical status in coffee roasting – and it deserves it. A key stage in any roast, understanding it will give you insight into how flavors and aromas are developing.
As the name suggests, this is the temperature at the end of your roast.
By understanding what’s going on inside the roaster at these key points, you’ll be able to start evaluating the impact of them on your beans. For example, by manipulating charge temp you can speed up or slow down your roast. The duration of first crack can affect body. Roasting graphs may, at first, be challenging. There’s a lot of data to collect and understand. However, as you start to work with air temperature, rate of rise, first crack, and more, you will begin to gain real mastery over how your coffee beans develop during roasting. So don’t be intimidated by these charts – start recording those temperatures and see how it helps you as a roaster. As heat is applied to the coffee beans, they go through endothermic and exothermic reactions. Up until first crack, the beans absorb the heat (an endothermic reaction). The moisture dissipates and the color changes from green to yellow and then brown. The aroma will be cereal-like: think toast, popcorn, or grass. As for first crack, this is a brief exothermic reaction: the beans release heat (energy) in the form of that steam we mentioned above, along with carbon dioxide. The bean will have doubled in size and shed the majority of their silver skin, but oils won’t yet be present. After first crack, it switches back to an endothermic reaction until second crack, the final exothermic reaction (if you choose to roast your beans that far).