Grind Size and Processing: A Pour-Over's Perfect Match

Question: When selecting beans for a pour-over, how might the processing method affect the ideal grind size I should aim for?

The Foundation of Flavor: Processing Methods

When embarking on the journey of brewing pour-over coffee, the quest for the perfect cup often leads us to meticulously select beans based on origin, roast profile, and tasting notes. However, a critical, yet sometimes overlooked, factor influencing the final brew is the coffee bean’s processing method. This culinary step, occurring after harvesting and before roasting, profoundly impacts the bean’s internal structure, solubility, and ultimately, how it interacts with water during extraction [6]. Understanding these processing nuances is key to dialing in the ideal grind size for your pour-over, ensuring a balanced and flavorful cup.

Washed vs. Unwashed: A Grind-Size Divide

Coffee processing methods can be broadly categorized, with the washed (or wet) process and natural (or dry) process being two of the most prominent. In the washed process, the fruit pulp is removed before the beans are dried. This method tends to produce cleaner, brighter coffees, emphasizing the inherent acidity and delicate floral or fruity notes [4]. Because the mucilage is removed, washed beans often exhibit a less dense structure. For pour-over, this can translate to a need for a slightly finer grind. A finer grind increases the surface area in contact with the water, allowing for more efficient extraction of soluble compounds and preventing under-extraction, which can manifest as a sour or weak cup.

Conversely, the natural process involves drying the coffee cherry with the fruit intact. This method allows the bean to absorb sugars and other compounds from the fruit during the drying phase, often resulting in coffees with more pronounced sweetness, body, and fruity, sometimes wine-like, characteristics [5]. The retained fruit material can lead to denser beans, which may require a coarser grind. A coarser grind in this scenario helps to avoid over-extraction, preventing the brew from becoming bitter or cloying. The increased density of naturally processed beans can mean that water moves through them at a different rate, making grind size adjustment crucial for optimal flavor development.

Honey Processing and Fermentation: Intermediate Pathways

Beyond the stark contrast of washed and natural, honey processing (or pulped natural) occupies a middle ground. Here, some or all of the mucilage is left on the bean during drying. This method can yield coffees with a balance of sweetness, acidity, and body, often exhibiting complex fruit notes. The presence of residual mucilage can influence bean density differently than a fully washed bean, potentially leaning towards a grind size that is slightly finer than a fully natural but perhaps coarser than a typical washed coffee. The specifics can vary greatly depending on the exact amount of mucilage retained and drying conditions.

Furthermore, fermentation plays a role in some processing methods, with controlled aerobic and anaerobic treatments known to positively influence pH, acidity, and volatile compound concentrations [3]. These alterations in the bean’s chemical makeup can affect its solubility and extraction profile. While specific grind size recommendations tied to fermentation duration or pH levels are not extensively detailed, it’s understood that altered bean chemistry will necessitate recalibration of brewing parameters, including grind size, to achieve the desired sensory outcomes.

The Influence of Particle Size on Extraction

Regardless of the processing method, the principle remains that grind size dictates the surface area available for water to interact with the coffee grounds. A finer grind offers a larger surface area, leading to quicker extraction, while a coarser grind reduces surface area, slowing down extraction [7]. This relationship is fundamental to achieving a balanced pour-over. The goal is to find a grind size that allows for sufficient extraction of desirable flavor compounds without pulling out too many undesirable ones, which often happens with over-extraction. For denser beans resulting from certain processing methods, a coarser grind might be necessary to allow adequate water flow and extraction within the typical pour-over brewing time. Conversely, less dense beans may benefit from a finer grind to ensure sufficient extraction.

Conclusion: A Holistic Approach to Brewing

Ultimately, the processing method is a vital piece of the puzzle when selecting beans for your pour-over. While roast level and bean origin are paramount, the subtle yet significant changes induced by processing—whether through the removal of fruit, the retention of mucilage, or controlled fermentation—alter the bean’s physical and chemical properties. This necessitates an adjustment in grind size to achieve optimal extraction. By considering how a bean was processed, you can make more informed decisions about your grind setting, moving closer to that perfectly balanced and aromatic pour-over every time. Experimentation remains key, but understanding these underlying principles provides a robust framework for your brewing endeavors.

References

[1] — Ernesto Illy, Luciano Navarini — Neglected Food Bubbles: The Espresso Coffee Foam. — 2011-Sep — https://pubmed.ncbi.nlm.nih.gov/21892345/ [2] — Magdalena Zdanowicz, Marta Rokosa, Magdalena Pieczykolan, Adrian Krzysztof Antosik, Katarzyna Skórczewska — Biocomposites Based on Wheat Flour with Urea-Based Eutectic Plasticizer and Spent Coffee Grounds: Preparation, Physicochemical Characterization, and Study of Their Influence on Plant Growth. — 2024-Mar-06 — https://pubmed.ncbi.nlm.nih.gov/38473683/ [3] — Gustavo Galarza, Jorge G Figueroa — Volatile Compound Characterization of Coffee ( — 2022-Mar-21 — https://pubmed.ncbi.nlm.nih.gov/35335365/ [4] — Katarína Poláková, Alica Bobková, Alžbeta Demianová, Marek Bobko, Judita Lidiková, Lukáš Jurčaga, Ľubomír Belej, Andrea Mesárošová, Melina Korčok, Tomáš Tóth — Quality Attributes and Sensory Acceptance of Different Botanical Coffee Co-Products. — 2023-Jul-11 — https://pubmed.ncbi.nlm.nih.gov/37509767/ [5] — Rongsuo Hu, Fei Xu, Xiao Chen, Qinrui Kuang, Xingyuan Xiao, Wenjiang Dong — The Growing Altitude Influences the Flavor Precursors, Sensory Characteristics and Cupping Quality of the Pu’er Coffee Bean. — 2024-Nov-28 — https://pubmed.ncbi.nlm.nih.gov/39682914/ [6] — Erol Uman, Maxwell Colonna-Dashwood, Lesley Colonna-Dashwood, Matthew Perger, Christian Klatt, Stephen Leighton, Brian Miller, Keith T Butler, Brent C Melot, Rory W Speirs, Christopher H Hendon — The effect of bean origin and temperature on grinding roasted coffee. — 2016-Apr-18 — https://pubmed.ncbi.nlm.nih.gov/27086837/ [7] — Benedikt K L Schmieder, Verena B Pannusch, Lara Vannieuwenhuyse, Heiko Briesen, Mirjana Minceva — Influence of Flow Rate, Particle Size, and Temperature on Espresso Extraction Kinetics. — 2023-Jul-28 — https://pubmed.ncbi.nlm.nih.gov/37569140/