The Coffee Aroma: Lost In The Modern Brew?

Coffee is a beloved beverage for many, with its rich aroma and flavour notes of chocolate, caramel, almonds, fruits, and flowers. However, some coffee enthusiasts have noticed a change in their favourite brew, with the once-potent aroma fading away, leaving them wondering: what happened to the aroma of coffee? This phenomenon may be attributed to various factors, including the quality of the coffee, the roasting and brewing processes, and the chemical compounds that create the unique fragrance of coffee.

The role of volatile compounds

The aroma of coffee is a result of a series of transformations from the seed to the cup. The aroma compounds are created during the roasting process, which involves the Maillard reaction, degradation, and decomposition of compounds in the coffee beans. These aroma compounds are volatile compounds, which are organic compounds that easily evaporate at room temperature and pressure.

Volatile compounds have to be airborne to be detected by the nose. Therefore, only compounds with high volatility will contribute to the aroma. The volatility of a compound depends on its size, with larger compounds like melanoidins, which contribute to coffee's colouration, having low volatility and thus not contributing to the aroma.

The aroma compounds are created through a variety of ways, but they are commonly produced as a consequence of the roasting process. The Maillard reaction, which occurs between proteins and sugars in the coffee beans, is a big contributor to the formation of aroma compounds. Additionally, the degradation and decomposition of other compounds in the coffee beans can also produce aroma compounds.

The roasting process can be visualised by following the formation of volatiles, which peak at different time points. For example, the compound tentatively assigned to formic acid peaks at a different time point than the compound tentatively assigned to methanol.

The aroma of coffee can be divided into two types: orthonasal and retronasal aroma. Orthonasal aroma refers to the smell of coffee before consumption, while retronasal aroma refers to the aroma released in the mouth when drinking coffee. Volatile organic compounds (VOCs) are released from the coffee and reach the olfactory epithelium, which contains the nerve endings that allow us to smell.

The composition of green coffee beans' VOCs is very different from that of roasted coffee beans. Green coffee beans do not contain any of the important coffee aroma compounds, which include furanones, phenols, and sulfur-containing compounds. However, similar groups of compounds can be observed in both green and roasted coffee beans.

The aroma of coffee is influenced by a variety of factors, including the variety of the bean, weather conditions, level of maturation, and processing choices. The aroma is also affected by the extraction method, with different molecules being extracted at different rates depending on their solubilities and polarities.

Overall, the unique aroma of coffee is a result of the complex interaction of various volatile compounds, which are formed during the roasting process and extracted during the brewing process.

How aroma is created and perceived

Coffee aroma is the fragrance of brewed ground coffee when infused with hot water. It is one of the primary qualities of coffee, denoting its flavour along with body, acidity, sweetness, bitterness, and aftertaste.

How Aroma is Created

When coffee beans are raw (in their green form), they have very little aroma. It is only during the roasting phase that the aroma develops due to the creation of various volatile compounds. The aroma precursors are various forms of carbohydrates, proteins, and acids. During the roasting process, they are transformed into volatile compounds. Different compounds create different sensory characteristics during roasting, and the level of roast can further impact how we perceive the aroma.

The complexity of aromas depends on the composition of chemical compounds in the green beans. These precursors of volatile compounds have different concentrations depending on several variables, including variety, weather conditions, level of maturation, and processing choices.

How Aroma is Perceived

Coffee aroma is perceived in two ways: nasally (through the nose) and retronasally. Retronasal perception occurs when the coffee is either in the mouth or has been swallowed, and aromatic volatile compounds drift up into the nasal passage.

When we smell coffee grounds, the molecules are freely interacting with our olfactory receptors. When the grounds are added to water, other molecules are extracted, and we have a different sensory experience.

It is estimated that more than 900 aromatic volatile compounds are produced during roasting, but only around 30 of them effectively contribute to the aromas and flavours we perceive. The compounds also need to be in balance for us to have a specific sensory experience.

The perception of the coffee's fragrance comes naturally by simply moving the cup toward the face. If you stop for a moment and smell the cup long and slowly, you will perceive more varied and complex notes.

Aroma and Flavour

Aroma and flavour are closely related but distinct. Flavour is the sense experienced by the tongue, while aroma is the smell. However, what we perceive as flavour is often actually aroma. When these combine with the aroma sensed by the receptors in the nose, we get flavour.

A coffee's aroma is also related to its flavour and acidity. For example, if a coffee is rich in flavour, the aroma will reflect that richness, and an acidic coffee will smell acidic.

Understanding how aroma is created and perceived can help us make more informed decisions on how to brew and recognise why various levels of extraction can taste and smell so different.

The importance of aroma to the tasting experience

The aroma of coffee is an essential part of the coffee experience. It is responsible for many of the flavour attributes not directly perceived by the tongue. With over 800 aromatic compounds in coffee, it has a huge impact on our perception of its flavour.

The science of aroma

Coffee aroma is created by the coffee's volatile vapours and gases, which are released from the brewed coffee and then inhaled through the nose, where they come into contact with the olfactory (nasal) membranes. These aromatic compounds are created through the chemical and biological reactions that occur during the roasting process. Green coffee beans have a minimal aroma, but when roasted, various volatile compounds are created, which give coffee its unique aroma.

Aroma and flavour

The terms aroma, taste and flavour are often used interchangeably, but they refer to different ways of experiencing coffee. Aroma is an odour sensed in the nose and at the back of the mouth. Taste is sensed by the tongue. Flavour is a holistic term that encompasses both taste and aroma.

Aroma and memory

The sense of smell is linked to memory and emotion. It is a powerful sense for evoking memories and emotions, and it is a form of language that has a deep connection with both. Smells are more easily associated with memories than visual or auditory signals, and they can trigger sensory sparks in our memory, creating expectation, which is a strong vehicle for emotions.

Aroma and freshness

Aroma also has a significant impact on the freshness of coffee. Roasted coffee beans become more porous, making it easier for the aromatic compounds to escape. If the coffee is not properly stored, it will quickly lose its aromatic compounds, becoming flat and flavourless.

Aroma and tasting

Aroma adds a lot to the sensory landscape of coffee, and it is important to learn to appreciate it apart from the other flavours. When tasting coffee, it is recommended to first give the coffee a good smell, then take a sip and swallow. The flavours that appear as you swallow are the aromas rising to your retronasal passage.

The impact of storage on aroma retention

The aroma of coffee is a complex interplay of chemical compounds, which are formed during the roasting process and extracted during the brewing process. The roasting process creates volatile compounds, which are responsible for the aroma of coffee. The Maillard reaction, which occurs between proteins and sugars in the coffee beans, is a significant contributor to the formation of these compounds. Additionally, the degradation and decomposition of other compounds in the coffee beans can also produce aroma compounds.

The storage of coffee beans can have a significant impact on aroma retention. It is important to note that the aroma of freshly roasted coffee is ephemeral, and appropriate packaging and storage are necessary to preserve its freshness. After a coffee package is opened, the protective atmosphere changes, accelerating the loss of freshness and the staling of the coffee. Different storage methods, such as using airtight canisters or closing the original package with tape, can affect the rate of freshness loss.

The water content of roasted coffee beans also plays a crucial role in aroma retention. Higher moisture content can lead to coarser particles upon grinding, and equilibration time prior to grinding is necessary to improve grinding results. During storage, the evolution of certain aroma compounds, such as hexanal and sulfides, is highly sensitive to water content. Additionally, moisture content can impact the stability of aroma compounds, with lower water content generally resulting in better aroma stability.

The level of roast can also influence aroma retention during storage. Lighter roast coffees tend to exhibit smaller changes due to storage conditions, while darker roast coffees may undergo more noticeable alterations. This is possibly due to differences in the overall volatile content, with darker roasts having higher levels of certain aroma compounds.

Overall, the impact of storage on coffee aroma retention is multifaceted and depends on various factors such as packaging, water content, level of roast, and storage conditions.

The chemical compounds behind the aroma of coffee

Coffee's aroma is a complex interplay of chemical compounds, with over 800 aromatic compounds identified. These compounds are created during the roasting process, with the most well-known being the Maillard reaction, which produces a range of products from the reaction between proteins and sugars in the coffee beans. The distinct aroma of coffee is due to volatile compounds, which easily evaporate at room temperature and pressure, allowing them to be detected by our noses.

Coffee beans contain a variety of constituents, with chlorogenic acid being the most prevalent in green, unroasted beans. When these beans are roasted, the heat breaks down these constituents, forming new compounds, including the distinctive aroma substances. The longer the beans are roasted, the more aroma compounds are produced, shaping the coffee's flavour profile.

The aroma compounds in coffee can be broadly classified into three categories: natural, nature-identical, and artificial. Natural aroma compounds originate from plant or animal sources, so the compounds in coffee beans are considered natural. These compounds are water-soluble, making hot water an effective method for extracting their flavour.

There are several families of compounds that contribute to the aroma of coffee. Sulfur-containing compounds, such as 2-furfurylthiol, have a roasted coffee aroma. Aldehydes add fruity, green aromas, while furans contribute caramel-like odours, and pyrazines have an earthy scent. Guaiacol and related phenolic compounds offer smoky, spicy tones, and pyrroles and thiophenes are also present in low concentrations.

The perception of coffee aroma is influenced by both the concentration of the compound and its odour threshold, with a small group of compounds with high concentration and low odour threshold likely making up the fragrance we know as coffee aroma. The interaction of these compounds also plays a role in the overall aroma, with some enhancing sweetness or other flavours.

The science behind coffee's aroma is complex, and researchers continue to explore the many chemical reactions and compounds that contribute to its distinctive fragrance.

Frequently asked questions