Unlocking Uniformity: Achieving Even Extraction in Your Chemex Brew

Question: How can I get a more even extraction when brewing with a Chemex?

The Foundation: Grind Size and Bed Preparation

The journey to an even Chemex extraction begins long before the hot water meets the grounds. A critical factor is the grind size. While specific recommendations can vary, the general consensus among brewing guides and research points towards a medium to medium-coarse grind for pour-over methods like the Chemex. Too fine a grind can lead to over-extraction, resulting in bitterness, and can also clog the filter, impeding water flow. Conversely, too coarse a grind will result in under-extraction, yielding a weak and sour cup. The presence of ‘fines’ – small coffee particles – can significantly impact extraction dynamics by altering the coffee bed’s permeability [6]. Therefore, using a quality burr grinder that produces a consistent particle size distribution is paramount. Beyond the grind, ensuring an even bed of coffee grounds within the filter is crucial. Gently shaking the dripper to level the grounds before brewing can help prevent channeling, a phenomenon where water finds preferential paths through the coffee bed, leading to uneven extraction.

The Crucial Bloom: Releasing Aromatics and Gases

The bloom is an essential first step in pour-over brewing, allowing the coffee to degas and prepare for optimal extraction. When hot water first encounters fresh coffee grounds, it triggers a release of carbon dioxide [2]. This release can create a frothy layer on top of the coffee bed. Allowing sufficient time for this bloom, typically 30-45 seconds, is vital. This initial wetting phase ensures that all grounds are saturated and ready to receive the subsequent water. Proper blooming facilitates a more uniform interaction between water and coffee particles, contributing to a more even extraction of soluble compounds [2, 5]. Without adequate blooming, pockets of coffee may remain hydrophobic, leading to under-extracted areas in the final brew.

Mastering the Pour: Technique and Consistency

The way water is introduced to the coffee grounds plays a significant role in achieving an even extraction. Pouring technique should aim for a controlled and consistent flow. Many experienced brewers advocate for a spiral pouring motion, starting from the center and working outwards, then returning to the center. This helps to saturate the grounds evenly and prevent the coffee bed from collapsing. Pouring too quickly can create turbulence and lead to channeling, while pouring too slowly might not provide enough agitation for optimal extraction. The water should be introduced in pulses rather than a continuous stream, especially during the initial stages after the bloom. Maintaining a consistent pour rate and volume throughout the brewing process is key to a balanced extraction [7]. The goal is to keep the coffee bed saturated without creating excessive agitation that could dislodge finer particles and negatively impact the extraction.

Beyond the Basics: Water Temperature and Ratios

While the preceding steps lay the groundwork, water temperature and the coffee-to-water ratio also contribute to the final cup’s quality. Research indicates that temperature is a critical factor in the extraction process [7]. For pour-over coffee, an optimal water temperature typically falls between 90°C and 96°C (195°F and 205°F). Temperatures too low can lead to under-extraction, while excessively high temperatures can scald the grounds and extract undesirable bitter compounds. Similarly, the coffee-to-water ratio, often expressed as grams of coffee to milliliters of water, directly influences the strength and extraction yield. While specific ratios are often a matter of personal preference, a common starting point for pour-over is around a 1:15 to 1:17 ratio. Experimentation within this range, combined with adjustments to grind size and pour rate, can help dial in the perfect extraction for your specific beans and brewing setup.

In conclusion, achieving an even extraction in a Chemex is a multifaceted endeavor that rewards careful attention to detail. By understanding the impact of grind size, the importance of the bloom, the precision required in pouring, and the influence of water temperature and ratios, enthusiasts can consistently brew a more balanced, aromatic, and flavorful cup of coffee.

References

[1] — 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/ [2] — Gustavo Galarza, Jorge G Figueroa — Volatile Compound Characterization of Coffee ( — 2022-Mar-21 — https://pubmed.ncbi.nlm.nih.gov/35335365/ [3] — Qiuming Li, Qingcai Hu, Xiaoxi Ou, Jihang He, Xinru Yu, Yunzhi Hao, Yucheng Zheng, Yun Sun — Insights into “Yin Rhyme”: Analysis of nonvolatile components in Tieguanyin oolong tea during the manufacturing process. — 2024-Oct-30 — https://pubmed.ncbi.nlm.nih.gov/39253009/ [4] — Rongsuo Hu, Fei Xu, Liyan Zhao, Wenjiang Dong, Xingyuan Xiao, Xiao Chen — Comparative Evaluation of Flavor and Sensory Quality of Coffee Pulp Wines. — 2024-Jun-27 — https://pubmed.ncbi.nlm.nih.gov/38999011/ [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] — Samo Smrke, André Eiermann, Chahan Yeretzian — The role of fines in espresso extraction dynamics. — 2024-Mar-07 — https://pubmed.ncbi.nlm.nih.gov/38453983/ [7] — Nur Hadiyani Zakaria, Kanyawee Whanmek, Sirinapa Thangsiri, Wimonphan Chathiran, Warangkana Srichamnong, Uthaiwan Suttisansanee, Chalat Santivarangkna — Optimization of Cold Brew Coffee Using Central Composite Design and Its Properties Compared with Hot Brew Coffee. — 2023-Jun-19 — https://pubmed.ncbi.nlm.nih.gov/37372624/ [8] — Shawn Gouws, Michael Muller — Valorization of products from grounded-coffee beans. — 2021-Oct-14 — https://pubmed.ncbi.nlm.nih.gov/34650157/