Decoding Bitterness: Troubleshooting Over-Extracted Coffee

Question: How can I identify and adjust for over-extraction when my coffee tastes too bitter or harsh?

The Culprits Behind Bitterness

A bitter or harsh taste in your coffee is frequently an indicator of over-extraction. This occurs when too many soluble compounds are dissolved from the coffee grounds into the water. While some bitterness is inherent to coffee and can even be desirable in certain contexts, excessive bitterness detracts from the nuanced flavors that coffee offers [4, 7]. This over-extraction can strip away the pleasant sweetness and delicate aromas, leaving a predominantly acrid profile.

Identifying the Signs and Adjusting Your Brew

Over-extraction is a common challenge, but thankfully, it’s often rectifiable through careful attention to brewing parameters. The primary way to combat over-extraction is by altering the grind size of your coffee beans. If your coffee tastes too bitter or harsh, a finer grind is likely the issue. A finer grind presents more surface area to the water, leading to faster and more extensive extraction. Therefore, the most straightforward adjustment is to coarsen your grind [4].

Beyond grind size, brew time plays a critical role. Longer contact between coffee grounds and water increases the likelihood of extracting undesirable bitter compounds. If you suspect over-extraction, try reducing your brew time. This is particularly relevant for methods like pour-over or immersion brewing. For espresso, the total dissolved solids and contact time are closely managed. While brew temperature has been shown to have a relatively minor impact on the sensory profile when brew strength and extraction are kept constant, excessively high temperatures can accelerate extraction and potentially contribute to bitterness [8]. Aiming for a water temperature in the range of 90-96°C (195-205°F) is generally recommended, but minor adjustments may be necessary based on your specific coffee and equipment [3].

The Role of Coffee Variety and Processing

While not directly an extraction parameter, the type of coffee bean and its processing can influence its inherent bitterness and its susceptibility to over-extraction. Different coffee species, such as Coffea arabica and Coffea canephora (robusta), have varying chemical compositions that affect flavor profiles and foam stability in espresso [1, 3]. For instance, Coffea arabica generally exhibits a more acidic profile compared to Coffea canephora, and its pH values can be lower [3]. Furthermore, the fermentation process during coffee processing can significantly impact volatile compounds and acidity, influencing the final taste. Aerobic and anaerobic fermentation treatments have been shown to positively affect pH and acidity, contrasting with the inhibitory effect of CO₂ treatments [2]. Understanding these intrinsic qualities can help you anticipate and manage potential bitterness issues.

Conclusion

Achieving a perfectly balanced cup of coffee is a journey of refinement. When bitterness or harshness clouds your palate, it’s a strong signal that your extraction has gone too far. By systematically adjusting your grind size towards coarser settings, reducing brew time, and ensuring your water temperature is within the optimal range, you can steer your brew away from over-extraction and unlock the complex, delightful flavors that your coffee has to offer. Experimentation is key, so don’t hesitate to make small, incremental changes to find your ideal extraction point.

References

[1] — Ernesto Illy, Luciano Navarini — Neglected Food Bubbles: The Espresso Coffee Foam. — 2011-Sep — https://pubmed.ncbi.nlm.nih.gov/21892345/ [2] — Gustavo Galarza, Jorge G Figueroa — Volatile Compound Characterization of Coffee ( — 2022-Mar-21 — https://pubmed.ncbi.nlm.nih.gov/35335365/ [3] — 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/ [4] — 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/ [5] — 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/ [6] — Adriana S Franca, Emiliana P Basílio, Laís M Resende, Camila A Fante, Leandro S Oliveira — Coffee Silverskin as a Potential Ingredient for Functional Foods: Recent Advances and a Case Study with Chocolate Cake. — 2024-Dec-05 — https://pubmed.ncbi.nlm.nih.gov/39683007/ [7] — Laurianne Paravisini, Ashley Soldavini, Julie Peterson, Christopher T Simons, Devin G Peterson — Impact of bitter tastant sub-qualities on retronasal coffee aroma perception. — 2019 — https://pubmed.ncbi.nlm.nih.gov/31581213/ [8] — Mackenzie E Batali, William D Ristenpart, Jean-Xavier Guinard — Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee. — 2020-Oct-05 — https://pubmed.ncbi.nlm.nih.gov/33020560/