Volatility in coffee (not the market)
Many reactions occur in the roasting process, some of those reactions add to the flow or and body of coffee. Other reactions take a way character.
We think it’s interesting to consider all of the physical things that have to precisely occur for your cup of coffee to become what it is.
The basic workflow of roasting coffee is
Sorting
Roasting
Cooking
Packaging
The process that needs the most explanation is probably roasting, that’s where most of the magic happens (if you’ve started with a great high quality bean).
Did you know?
It takes only 18 minutes or so to roast about 25 lbs. of coffee to a light roast.
Of course the roast time depends on many factors like the kind of bean, the type of roast, the rate of rise (RoR) of the heat, etc. Knowing when to apply heat and when to lay off is the art of the magic of roasting.
When beans are roasting they go through several key scientific processes that ultimately effect the character of your cup:
The Maillard reaction! Yummy part that we love so much in any food method where browning occurs. When roasters experiment with roast profiles, it includes varying the length and intensity of Maillard reaction and recording its effects on profile.
The Strecker Degradation depends on the Maillard reaction (it’s highly scientific - think the formation of ketones and aldehydes) but it’s important because it produces the all important aroma and flavor compounds.
Caramelization of sugars occurs when amino acids react with reducing sugars at around 170°C/338°F, heat causes large, complex carbohydrates to break down into smaller sugar molecules that can be dissolved in water. This means that the perceived sweetness level of your finished brew increases.
Which brings us to volatile and non-volatile compounds.
Volatile compounds are organic chemicals that have a high vapor pressure at room temperature. When aroma-producing volatile compounds disperse, we experience that signature coffee smell.
These include:
Aldehydes, which add fruity, green aromas.
Furans, which contribute caramel odors
Pyrazines, which have an earthy scent.
Sulfur-containing compounds, including 2-furfurylthiol. Some of these have an aroma that is commonly described as “roasted coffee” but there are others that don’t smell as appealing in isolation. For example, methanethiol smells like rotten cabbage.
Guaiacol, which has smoky, spicy tones.
Non-volatile compounds are simply substances that are stable at room temperature. That is, they don’t vaporize. Some of these compounds are changed during roasting, whereas others remain stable through the process. Many non-volatile compounds contribute to flavor and profile.
Examples include caffeine, which is responsible for some bitter flavors. Caffeine is naturally occurring in coffee and remains unchanged by the roasting process. Other non-volatile compounds include sucrose, which provides sweetness, and lipids, which provide body and mouthfeel. The melanoidins that create color and body are also non-volatile compounds.
The Role of Acids
Acids play an important role in creating flavor and are sensitive to heat. Roasting can degrade some acids and create others.
For example, the citric and tartaric acids that produce fruity and sweet notes are broken down during roasting so a long or overly hot roast can hugely reduce the sweetness of the final profile.
This is particularly important when it comes to single-origin coffees. If you roast a coffee bean for too long you will diminish the compounds that define the character of the origin and that particular bean.
If you made it this far...
Coffee roasting includes a number of chemical transformations that contribute to the flavor, aroma, and body of your finished cup. Many of these reactions are sensitive to variations in temperature and length of exposure to heat. So a small change in roasting (or even brewing) technique can have a profound impact on a coffee’s profile.
