Zurich University of Applied Sciences , Institute of Chemistry and Biotechnology, Coffee Excellence Center , Einsiedlerstrasse 31 , 8820 Wädenswil , Switzerland.
Suntory Beverage & Food Limited , Tokyo 104-0031 , Japan.
J Agric Food Chem. 2018 May 30;66(21):5293-5300. doi: 10.1021/acs.jafc.7b03310. Epub 2017 Nov 15.
During the roasting of coffee, thermally driven chemical reactions lead to the formation of gases, of which a large fraction is carbon dioxide (CO). Part of these gases is released during roasting while part is retained inside the porous structure of the roasted beans and is steadily released during storage or more abruptly during grinding and extraction. The release of CO during the various phases from roasting to consumption is linked to many important properties and characteristics of coffee. It is an indicator for freshness, plays an important role in shelf life and in packaging, impacts the extraction process, is involved in crema formation, and may affect the sensory profile in the cup. Indeed, and in view of the multiple roles it plays, CO is a much underappreciated and little examined molecule in coffee. Here, we introduce an accurate, quantitative, and time-resolved method to measure the release kinetics of gases from whole beans and ground coffee using a gravimetric approach. Samples were placed in a container with a fitted capillary to allow gases to escape. The time-resolved release of gases was measured via the weight loss of the container filled with coffee. Long-term stability was achieved using a customized design of a semimicro balance, including periodic and automatic zero value measurements and calibration procedures. The novel gravimetric methodology was applied to a range of coffee samples: (i) whole Arabica beans and (ii) ground Arabica and Robusta, roasted to different roast degrees and at different speeds (roast air temperatures). Modeling the degassing rates allowed structural and mechanistic interpretation of the degassing process.
在咖啡烘焙过程中，热驱动的化学反应导致气体的形成，其中很大一部分是二氧化碳（CO）。这些气体的一部分在烘焙过程中释放，而一部分则被保留在烘焙豆的多孔结构内部，并在储存过程中逐渐释放，或者在研磨和提取过程中更迅速地释放。从烘焙到消费的各个阶段，CO 的释放与咖啡的许多重要性质和特征有关。它是新鲜度的指标，在保质期和包装中起着重要作用，影响萃取过程，参与 crema 的形成，并可能影响杯中感官特征。事实上，鉴于其发挥的多种作用，CO 是咖啡中一种被严重低估和研究不足的分子。在这里，我们介绍了一种准确、定量且时间分辨的方法，使用重量法来测量整个咖啡豆和研磨咖啡中气体的释放动力学。将样品放置在带有适配毛细管的容器中，以使气体逸出。通过充满咖啡的容器的重量损失来测量气体的时间分辨释放。通过半微量天平的定制设计实现了长期稳定性，包括周期性和自动零点测量和校准程序。新的重量法被应用于一系列咖啡样品：（i）整粒阿拉比卡豆和（ii）研磨的阿拉比卡和罗布斯塔，以不同的烘焙程度和不同的速度（烘焙空气温度）烘焙。对脱气速率进行建模，允许对脱气过程进行结构和机制解释。
