The Sweet Science of Coffee Brewing – Insights from Drip Brew Studies
Coffee brewing is a fascinating process where science meets artistry, and every cup is a complex interplay of chemistry, timing, and technique. In a study by Batali et al. (2020), researchers investigated how coffee’s sensory and chemical properties change throughout the brewing process. Their findings not only reveal the nuances of drip brewing but also challenge traditional assumptions about sweetness in coffee. Here’s a closer look at what this study uncovered and what it means for your next cup.
Methods: Investigating Coffee Fractions
To understand how coffee evolves during brewing, the researchers used a drip-brewing method with consistent conditions:
Brewing Details: Coffee was brewed using a fixed coffee-to-water ratio and a medium grind size, with water at a controlled temperature of 93°C.
Fraction Collection: Samples of brewed coffee were collected every 30 seconds, resulting in multiple "fractions" of coffee from the same brewing session.
Analysis:
Sensory Evaluation: Trained sensory panels rated attributes like bitterness, sourness, astringency, sweetness, floral, fruity, and smoky notes.
Chemical Analysis: Levels of total dissolved solids (TDS) and monosaccharides (e.g., glucose and fructose) were measured in each fraction.
This detailed approach allowed researchers to correlate chemical properties with sensory perceptions across different brewing stages.
Results: Flavour Evolution in Drip-Brewed Coffee
Early Fractions: Intense and Robust
TDS: The initial fractions had the highest TDS values, meaning they were the strongest in terms of dissolved coffee compounds.
Sensory Attributes:
Dominated by bitterness, sourness, and astringency, consistent with the rapid extraction of water-soluble compounds like caffeine and chlorogenic acids.
Smoky and burnt flavours were most pronounced in these fractions, likely due to the rapid dissolution of darker roast compounds.
Middle Fractions: The Rise of Sweetness
As brewing progressed, the TDS levels began to decrease, yet sensory attributes shifted noticeably.
Sweetness emerged as a dominant attribute, alongside floral and fruity notes. This was surprising because chemical analysis revealed that monosaccharides (sugars) were present at levels far below sensory detection thresholds.
Hypothesis: The perceived sweetness was not driven by sugar content but rather by aromatic compounds and reduced levels of bitterness and sourness. This suggests that sweetness in coffee may be influenced by complex interactions between aroma and taste.
Later Fractions: Delicate and Floral
The final fractions had the lowest TDS values, resulting in lighter-bodied coffee.
Flavour Profile:
A notable increase in floral and honey-like notes, often associated with high-quality Arabica beans.
Sourness and astringency were minimal, leading to a smooth and pleasant taste.
The absence of overwhelming bitterness made these fractions ideal for highlighting delicate, nuanced flavours.
Discussion: Rethinking Coffee Sweetness
One of the most intriguing findings was the discovery that perceived sweetness was not linked to sugar content. In fact:
Chemical analysis showed that glucose and fructose levels were far below the sensory detection thresholds in all fractions.
Instead, sweetness was likely a result of:
Reduced bitterness and sourness in later fractions.
Volatile aroma compounds contributing to the perception of sweetness, floral notes, and fruity flavours.
This finding challenges traditional assumptions about sweetness in coffee and highlights the importance of aroma-taste interactions in shaping our sensory experiences.
Practical Insights for Coffee Enthusiasts
This study offers valuable lessons for home brewers and coffee professionals:
Experiment with Fractioning: By collecting and tasting different fractions of your brew, you can identify your preferred flavour profile—whether you enjoy bold and bitter notes or delicate floral nuances.
Blend Fractions for Customised Brews: Use earlier fractions for milk-based drinks where strong, robust flavours are needed, and later fractions for light, fruity black coffee.
Understand TDS: High TDS doesn’t always mean better flavour. Sometimes, lower TDS levels can reveal the subtle complexities of your coffee.
Conclusion: Crafting the Perfect Cup
The findings from this study underscore the dynamic nature of coffee brewing. Every stage of the brewing process contributes to the final cup, with early fractions offering bold strength and later fractions unveiling delicate sweetness and floral notes. By understanding how flavour evolves, coffee lovers can experiment with brewing techniques to create a cup that suits their preferences.
At Fission and Bloom, we celebrate the art and science of coffee brewing. Our speciality coffees, such as the Kelloo Ethiopian beans, are crafted to bring out the best in every cup. Try experimenting with brewing times and methods to uncover the unique flavours that make each coffee special. Visit our website to explore more brewing tips and discover the science behind your favourite coffee.
References:
Batali et al. Sensory and monosaccharide analysis of drip brew coffee fractions versus brewing time. Journal of the Science of Food and Agriculture. 2020:100;7;2953-62. https://scijournals.onlinelibrary.wiley.com/doi/abs/10.1002/jsfa.10323
