Comparative Study on the Espresso Extraction and Sensory Evaluation of Light vs. Medium Roasted Coffee

This study investigates the differential impact of coffee roast profiles – specifically, a lighter roast typically intended for filter brewing and a more developed medium roast designed for espresso preparation – on the sensory characteristics of coffee extracted using an espresso machine. Through a detailed analysis that includes an overview of the roasting methodologies and a comprehensive sensory analysis, this investigation presents blind tasting results from a panel of ten individuals—comprising both experienced coffee tasters and general coffee enthusiasts. The study further evaluates each roast profile’s performance in a milk-based beverage; a flat white, offering insights into the complex relationship between roast profile, extraction parameters, and sensory experience.

Introduction

The process of roasting coffee plays a pivotal role in defining the chemical composition and, consequently, the sensory characteristics of the final brew. Light roasts, often preferred for their high acidity and distinct flavour profiles in filter coffee, contrast with medium roasts, which are favoured for espresso due to their balanced acidity, enhanced sweetness, and prominent texture, achieved through a strategic roast development of more soluble compounds and sugar caramelisation. This study aims to dissect the sensory outcomes of using these divergent roast profiles in espresso extraction, a method renowned for its solubility efficiency.

Materials and Methods

Roasting Profiles

• Light Roast: Aimed at filter brewing, this profile employs a faster heat transfer methodology and concludes shortly after the first crack – preserving the beans’ intrinsic acidity and flavour nuances.
• Medium Roast: Optimised for espresso, this roast extends the development a little more beyond the first crack to promote lipid formation and sugar caramelisation, stopping well before the second crack to maintain a balance between body, sweetness, and acidity.

Sensory Analysis

Ten individuals (five coffee experts/professionals and five general consumers/coffee drinkers) conducted a structured sensory evaluation focusing on acidity, sweetness, texture/body, and overall flavour enjoyment, scoring each attribute on a scale of 0 to 6.

Brewing Parameters

In the preliminary phase of our study, the primary task was to determine an optimal extraction recipe that would best suit the distinct characteristics inherent to each roast profile. Recognising the inherent disparities between the light and medium roasts, it was clear that to unlock the full sensory potential of each, differential brewing adjustments would be indispensable. 

Crucially, while evaluating the extractability of the two roast profiles, it’s been proven  that the medium roast can achieve a yield ratio of 1:2.3 without sacrificing the harmony of flavour, sweetness, and body. On the other hand, the lighter roast exhibited its optimal sensory balance at a yield ratio of 1:1.8; exceeding this ratio while achieving enhanced flavour balance, resulted in an espresso that was perceived as overly thin/watery. This highlights the necessity of adapting extraction techniques to match the coffee’s roast profile, illustrating the intricate interplay between roast degree, extraction yield, and espresso quality.

However, to maintain the integrity and comparative essence of this study, and to facilitate a fair assessment, it was crucial to devise a unified extraction protocol applicable to both types of coffee. Thus, a standardised extraction methodology needs to be adopted, designed to highlight the distinct characteristics of each coffee while adhering to industry  benchmarks and brewing parameters.

Both coffees were assessed 12 days post-roast, employing a brewing recipe that took into consideration the more challenging parameters of the lighter roast. This included a 20g dose, a 38g yield, and a 28-second extraction time, performed at a steady 9 bars of pressure without preinfusion. The brewing water had a TDS measurement of 115 ppm, and the machine temperature was calibrated at 94°C.

Milk Beverage Preparation

Espresso shots from both roast profiles were utilised in preparing piccolo and flat white beverages, assessing dairy interaction through a standard milk-to-coffee ratio.

Disclaimer on Coffee Tasting Protocol

Each taster was concurrently presented with two cups, one light and one medium roast espresso, making scoring contingent on comparative rather than objective assessment.

Results

The table below displays detailed scores and comments from each of the 10 tasters on the sensory attributes, alongside more approachable consumer remarks and more technical expert comments.

Taster	Roast Profile	Acidity (0-6)	Sweetness (0-6)	Texture/Body (0-6)	Flavour Enjoyment (0-6)	General Comments
1 (Expert)	Light	5	2	2	3	“Marked citric acidity, with underwhelming body.”
1 (Expert)	Medium	3	5	5	5	“Exceptional balance, with a caramel-like sweetness.”
2 (Expert)	Light	4	3	2	4	“Pronounced acidity, lacking in sweetness and body.”
2 (Expert)	Medium	2	5	5	5	“Rich in flavour, with a perfect balance of sweetness.”
3 (Expert)	Light	5	2	1	3	“Bright acidity, but lacks body.”
3 (Expert)	Medium	3	4	4	4	“Well-rounded, with a pleasing texture.”
4 (Expert)	Light	4	2	2	3	“Dominant acidic notes, thin body.”
4 (Expert)	Medium	3	4	5	5	“Full-bodied, with a satisfying sweet finish.”
5 (Expert)	Light	5	3	1	4	“High acidity, minimal body.”
5 (Expert)	Medium	2	5	4	5	“Excellent sweetness and body, very enjoyable.”
6 (Consumer)	Light	3	2	3	2	“Tastes a bit sour, not really my preference.”
6 (Consumer)	Medium	3	4	4	4	“Smooth and sweet, much better than the light roast.”
7 (Consumer)	Light	4	1	2	2	“Quite sour, missed the mark for me.”
7 (Consumer)	Medium	3	4	4	4	“Loved this one, great sweetness and feels rich.”
8 (Consumer)	Light	3	2	2	3	“Sourish, not what I look for in a coffee.”
8 (Consumer)	Medium	2	5	5	4	“Yummy, the sweetness and body are on point.”
9 (Consumer)	Light	4	2	2	3	“Too sour for my liking, prefer the other one.”
9 (Consumer)	Medium	3	4	4	4	“This is good, nice balance and not too bitter.”
10 (Consumer)	Light	3	3	2	2	“Sour and a bit flat, not very exciting.”
10 (Consumer)	Medium	2	4	4	4	“Really enjoyable, a good balance of flavours.”

Overall Findings

The tests revealed a distinct preference for the medium roast profile across both expert tasters and general consumers, notably for its balance, enhanced sweetness, and fuller body. The light roast was consistently praised for its acidity but critiqued for lacking body and a more ‘obvious’ sweetness, critical attributes for an espresso experience. This preference highlights the importance of roast profile on sensory perception in espresso extraction, with a particular emphasis on the comparative, rather than objective, nature of the tasting protocol employed.

The aggregated data points to a nuanced understanding of how roast profiles influence sensory experiences, particularly in espresso preparation. The medium roast’s capacity to deliver a harmonious blend of sweetness, body, and flavour was clearly favoured, contrasting sharply with the light roast’s pronounced acidity, which, while appealing to some, was generally deemed too aggressive, especially when lacking in body and sweetness.

This preference highlights the importance of roast development in crafting espresso profiles that appeal to a broad audience. The medium roast’s performance underscores the value of a balanced approach to roasting, where lipid development and sugar caramelisation play pivotal roles in shaping the coffee’s sensory profile. The feedback from consumers, describing the light roast as “sour” or not to their taste, alongside the experts’ more detailed critique, provides a clear directive for roasters and baristas alike: balance and development are key to satisfying the diverse palates of espresso drinkers.

Considerations

While a couple of the experts showed a slight preference for the lighter roast, attributing their choice to its “exquisite acidity and sweetness,” the comparative data largely supports a broader preference for the medium roast, particularly noted for its balanced taste profile. The medium roast was consistently praised for its rich caramel sweetness, ideal texture/body, and overall flavour enjoyment, contrasting with the light roast’s criticism for excessive acidity and lack of body. Among consumers, the preference for the medium roast was even more pronounced, with feedback highlighting its enjoyable balance and approachability compared to the lighter roast’s challenging acidity.

The preferences exhibited by the panel suggest a nuanced appreciation for the complexity and balance that medium roasts bring to espresso, underlining the significance of developing roasting profiles that cater to the broader sensory expectations of both expert and everyday coffee drinkers.

Milk Beverage Evaluation Summary

Following the espresso tasting, both panels sampled both light and medium roast coffees as a flat white using the exact espresso recipe as the previous experiment. Here are their summarised observations:

Experts

• The medium roast was praised for its harmonious interaction with milk, enhancing the beverage’s overall sweetness and creating a velvety texture.
• Notably, one expert found the lighter roast surprisingly pleasant, citing a certain tangy quality that provided a refreshing contrast to the milk, albeit this was an anomaly.
• Overall, the medium roast was preferred for both milk beverages due to its balanced flavour profile, which was described as more rounded and complementary to the dairy components.

Consumers

• Consumers overwhelmingly preferred the medium roast in milk-based drinks, highlighting the enhanced sweetness and creamier texture as key factors.
• Several noted that the lighter roast resulted in a milk beverage that was perceived as less cohesive, with the coffee’s acidity clashing rather than melding with the milk.
• The feedback underlined a preference for the smooth and comforting taste of the medium roast, which was seen as more enjoyable and approachable in a milk context.

Discussion

The study’s results underscore the importance of roast profile in espresso extraction and its sensory impact, as espresso as well as being extended to milk-based beverages. The medium roast’s performance underscores the significance of achieving a balance between acidity, sweetness, and body – a balance that is not only preferred by experts within the specialty coffee community but more importantly by general coffee enthusiasts.. This broad preference for balanced flavour, seemingly also points to an elevated appreciation for specialty coffee among the general consumer base, highlighting a shift from the bitter-dominating commercial coffee arena and equally important – the need for the specialty coffee community to value and incorporate consumer feedback into their practices. 

The preference for medium roast profiles, particularly in the context of milk beverages, reiterates the importance of creating versatile coffee profiles that cater to both pure espresso shots and milk-based drinks. Acidity, while exciting and a hallmark of lighter roasts, presents trade-offs in espresso preparations, often resulting in a challenging balance when paired with milk. Moreover, the study noted that the reproducibility of espresso shots was more difficult with the lighter roast, likely due to its greater volatility and the finer tuning required to extract optimal flavour profiles. This variability underscores the barista’s role in consistently delivering high-quality coffee, with medium roasts offering a more forgiving and consistent basis for espresso extraction.

Understanding and addressing the trade-offs associated with acidity in lighter roasts, and acknowledging the technical challenges they pose in espresso preparation, are essential steps in fostering a more inclusive and diverse coffee culture that resonates with a wider audience.

Conclusion

This comparative study reveals a pronounced preference for medium roasts in espresso and milk-based coffee beverages, highlighting the critical role of balanced roast profiles in satisfying contemporary coffee palates. By embracing the feedback from both experts and general consumers, the specialty coffee community can enhance its offerings, ensuring that the coffee experience is enjoyable and accessible to all coffee enthusiasts. Further research and dialogue within the community will continue to refine these insights, driving innovation and excellence in coffee roasting and preparation.

Future Work

Future investigations could further explore the dynamics of roast profile preference across a broader spectrum of coffee preparations, including alternative brewing methods. Expanding the sensory analysis to include a wider range of tasters and diverse coffee origins could offer more nuanced insights into the complex relationship between roast profile, extraction technique, and sensory experience. Additionally, examining the impact of water quality and brewing parameters on the extraction of different roast profiles would provide valuable data to optimise the coffee brewing process further, tailoring it to meet the evolving tastes and preferences of the global coffee-drinking community.