Among coffee enthusiasts and casual drinkers alike, the meticulous art of roasting has long enchanted and intrigued those seeking the perfect brew. A recent study sheds light on a critical aspect of coffee brewing, revealing how different levels of roast impact the caffeine content and porosity in Ethiopian coffee. This discovery not only adds depth to our understanding of coffee chemistry but also offers practical insights for both professional roasters and home brewers.
The study, conducted by researchers from Berry College and Drexel University, meticulously analyzed two types of Ethiopian coffee beans: naturally processed and washed. To explore the influence of roasting, the research team subjected these beans to five distinct levels of roast, ranging from light to dark. The investigation centered on how these varying roast levels affect the caffeine concentration and the porosity of the coffee seeds.
Porosity, a key factor in coffee brewing, essentially refers to the tiny spaces within the roasted coffee beans. These spaces influence how water interacts with the coffee grounds during brewing, which in turn affects the extraction yield and the concentration of caffeine in the brew. The researchers utilized scanning electron microscopy to measure changes in porosity across different roast levels.
One of the standout findings of the study was the direct correlation between the degree of roast and porosity. As the degree of roast increased, so did the porosity of the coffee beans. Specifically, porosity measurements ranged from 13.6% for unroasted green coffee to 45.8% for the darkest roast batch. This increase in porosity is crucial because it indicates more pathways for water to extract soluble compounds from the coffee grounds, potentially enhancing the flavor and caffeine extraction.
However, the study also noted a critical balance. While increasing porosity generally aids in extraction, too much roasting can lead to significant losses of extractable compounds, including caffeine. The researchers found that caffeine content initially rises with the degree of roast but then decreases significantly at higher roast levels. This is attributed to the volatilization and breakdown of caffeine at temperatures exceeding 400-420°F during the roasting process.
The practical implications of these findings are significant. For coffee enthusiasts who prize a high caffeine content, it might be beneficial to opt for a medium roast, which appears to strike the right balance between maximizing caffeine extraction and minimizing its degradation. The study found that caffeine levels reached a peak in roast batches with about 14-16% mass loss, corresponding to medium roast levels, before declining in darker roasts.
Moreover, the research highlights that darker roasts tend to have lower extraction yields for caffeine. This is attributed to the fact that while darker roasts increase porosity, they also lead to the breakdown of other soluble compounds, complicating the extraction dynamics. Essentially, the increased porosity might facilitate easier extraction, but the loss of compounds due to high roasting temperatures reduces the overall caffeine content available in the brew.
This study represents one of the first quantitative analyses to compare caffeine content, extraction yield, and porosity as a function of degree of roast in Ethiopian coffee. It underscores the complex interplay between roasting and brewing, and how consumer preferences can be tailored by understanding these dynamics.
Zachary R. Lindsey, the lead researcher, explains, “Understanding the relationship between roast degree and extraction behavior is key to optimizing coffee brewing. We aim to provide guidelines that help achieve desired caffeine levels and flavor profiles, whether you’re a barista, roaster, or homebrewer.”
Studies like this offer valuable insights that could influence roasting techniques and coffee preparation methods worldwide as the coffee industry continues to evolve. For now, coffee lovers can take away a nugget of wisdom: the roast level you choose does more than define flavor; it intricately shapes the caffeine profile and the very essence of your coffee experience.
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Reference
Lindsey, Z.R., Williams, J.R., Burgess, J.S. et al. Caffeine content in filter coffee brews as a function of degree of roast and extraction yield. Sci Rep 14, 29126 (2024). https://doi.org/10.1038/s41598-024-80385-3
