Coffee science reveals that many factors contribute to the flavor of coffee: the variety, the roast profile, the brewing recipe, and the processing method. However, when you break it down, the profile of a coffee ultimately comes down to one thing: chemical compounds.
Coffee science shows that the way we roast the coffee, the type of beans we choose, and the altitude at which they are grown all impact these components. Yet, to truly optimize the coffee profile, it is crucial to understand the science behind it. This is particularly true for roasters, as their work involves manipulating heat to control various chemical reactions.
Coffee science is the focus of my PhD studies, where I aim to predict the flavor, aroma, and quality of coffee through the analysis of its chemical components. Let me share with you the key points you should know about coffee science.
Taste: The Chemistry Behind It
Aroma, flavor, aftertaste, acidity, and body: all five attributes are responses to various chemical compounds. At the cupping table, we analyze them using our senses, but chemical reactions are also at play. We evaluate the aroma first, then the scent as we break the coffee crust, and finally, we taste it. Each stage reveals different molecules.
As a Q grader, I enjoy tasting coffee, but as a scientist, I focus on the chemical compounds and their interactions. In coffee science, numerous non-volatile compounds influence flavor and quality, ranging from carbohydrates to caffeine. Their quantities will vary based on the quality of the green coffee, but it’s important to note that the chemical composition of green beans differs significantly from that of roasted beans.
This leads us to volatile compounds, which are primarily generated through chemical transformations during the roasting process. In coffee science, these compounds are crucial for determining the quality of coffee.
Some Non-Volatile Compounds
When discussing non-volatile compounds, it’s essential to highlight alkaloids (caffeine and trigonelline), chlorogenic acids, carboxylic acids, carbohydrates and polysaccharides, lipids, proteins, melanoidins, and minerals. Caffeine, for instance, influences the perceived strength, bitterness, and body of brewed coffee. It is soluble in water. Another key alkaloid is trigonelline, which contributes to the aroma of roasted beans and freshly brewed coffee.
In coffee science, chlorogenic acids are particularly fascinating to me. While they may not taste great, my research on them has been extensive.
What you should know about chlorogenic acids is that they consist of trans-cinnamic acids (such as caffeic, ferulic, and p-coumaric acids) and quinic acid. Let me clarify: quinic acid is responsible for the bitterness and astringency in coffee.
During roasting, chlorogenic acids break down, leading to an increase in quinic acid, which is one reason why very dark roasts can taste bitter.
Now, let’s talk about organic acids, which relate to the desirable acidity in coffee. This attribute is crucial for quality and is often associated with sweetness. Here are some important points:
- Arabica coffee is more acidic than Robusta.
- Acid content decreases during roasting (11% for green beans but only 6% for roasted beans).
- Dark roasts generally have lower acid content and perceived acidity.
In coffee science, we can categorize types of acidity: some of the most “sensitive” acids in coffee include citric, malic, and chlorogenic acids. While some acids degrade during roasting, such as chlorogenic acids, others increase in concentration, like formic, acetic, and lactic acids. Understanding these dynamics is crucial in coffee science for achieving the perfect cup.
Carbohydrates and polysaccharides are important in coffee science. Some polysaccharides, such as arabinogalactans, mannans, and cellulose, play a crucial role in retaining volatile compounds in coffee, which contributes to its aroma. In terms of flavor, these molecules also affect the viscosity of the beverage. Additionally, smaller sugars like glucose and fructose enhance the perceived sweetness of coffee.
Lipids are another key component that contributes to the texture of brewed coffee. They are extracted from the beans and are responsible for creating the crema in espresso. Interestingly, the roasting process does not alter their content levels, but during roasting, oils migrate to the surface of the beans, helping to trap volatile compounds inside.
Finally, we have melanoidins, which are products of the Maillard reaction: interactions between amino acids and the carboxyl group of reducing sugars. These large molecules give coffee its brown color and enhance the texture of the brew. This means that the amino acid content in coffee is closely linked to its quality; the more amino acids present, the more reactions occur, leading to increased melanoidins.
It’s important to note that the brown color of coffee isn’t solely due to melanoidins; it also results from the caramelization of sugars. This brings us to volatile compounds, which are essential in coffee science for understanding flavor and aroma profiles. Overall, grasping these components is vital in coffee science to enhance the quality of the final cup.
What Are Volatile Compounds?
Now we come to the most exciting topic of all: volatiles in coffee. There are countless volatile compounds present in coffee, and as I mentioned earlier, they are essential determinants of coffee quality.
These volatile compounds are primarily formed through chemical transformations during the roasting process. However, this doesn’t mean that green beans are irrelevant to their formation. Volatile compounds can reveal the coffee variety, the processing techniques used by farmers, and even the geographical origins of the coffee.
It’s safe to say that there are over 1,000 volatile compounds in coffee after roasting. Nevertheless, only a small number of these contribute to the perceived aroma. Several researchers suggest that around 20 to 30 volatiles are significant in our beverage. When analyzing the aroma, we must consider that it is likely more related to the concentration of a single compound and its correlation with others, along with your “threshold,” rather than the entire set of 1,000 compounds. (The threshold refers to the minimum concentration of a chemical that the human nose can detect.)
Understanding these dynamics is crucial in coffee science, as it allows us to appreciate the complexity of flavors and aromas in our coffee. By studying these volatile compounds, coffee science helps us improve quality and enhance the overall coffee experience. Ultimately, the role of volatiles is a fascinating aspect of coffee science that continues to inspire research and exploration.
How Chemical Reactions Produce Volatile Compounds
Let’s take a closer look at the chemical reactions that lead to these volatile compounds. The primary reactions involved are the Maillard reactions (non-enzymatic browning). We’ve already discussed this in relation to melanoidins; however, these reactions also produce nitrogen and sulfur-containing heterocyclic compounds.
Another important reaction to consider is the degradation of phenolic acid. This involves the breakdown of chlorogenic acids (remember those from the non-volatile compounds section?) to form caffeic acid (or other trans-cinnamic acids), lactones, and quinic acids. These compounds contribute to the bitterness and astringency in coffee.
The Strecker degradation is yet another significant reaction. It primarily occurs during the development stage of coffee roasting and involves the decomposition of amino acids into aldehydes and ketones, which enhance the aroma.
To be honest, there are at least seven more reactions that occur during roasting that we could discuss, but that’s a topic for another article. In my view, the roasting phase is like a grand chemical party happening inside the beans. A lot is going on!
Understanding these processes is essential in coffee science, as they directly impact the flavor and aroma profiles we experience in our cup. By studying these chemical reactions, coffee science allows us to refine roasting techniques and improve the overall quality of coffee. The intricate chemistry involved is what makes coffee science so fascinating and vital to the coffee-making process.
Identifying Specific Components and Flavor Profiles
These volatile compounds include hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, esters, pyrazines, pyrroles, pyridines, furans, furanones, phenols, and others.
While all of these terms may sound scientific and somewhat intimidating, they can all be traced back to specific attributes of coffee.
Have you tried the aroma game Le Nez du Café? It features 36 aromas that you can use to train your sensory skills. One of my favorites is apricot (number 16), which has a fresh, fruity scent. Generally, floral and fruity aromas result from ketones and aldehydes. If you look up the characteristics of number 16 in the accompanying book for Le Nez du Café, you’ll find that this aroma is associated with benzaldehyde, an aldehyde. Magnificent!
Furan and furanone are typically what lead us to perceive roasted coffee and caramel notes. Pyrazines can be linked to nutty and roasted coffee flavors. Of course, the quantity and interactions of some other compounds can also create negative notes; for instance, guaiacol molecules (phenolic compounds) are responsible for phenolic and burnt notes.
Understanding these connections is crucial in coffee science, as it helps us identify and appreciate the complex flavor profiles present in coffee. By examining these volatile compounds, coffee science enhances our ability to discern various aroma characteristics, ultimately improving our overall coffee experience. The intricate relationships among these compounds are what make coffee science a fascinating field of study.
I apologize, dear readers, but the world I’ve begun to explore seems limitless. This article serves merely as an introduction to the wonders of coffee chemistry: there’s so much more to discover. Let’s dive into this topic, whether through a science book or simply by enjoying a cup of coffee.
While everything ultimately ties back to the deep and complex realm of coffee science, we can always savor these compounds in our cup.