Electrical current might be the key to a better cup of coffee
Electrical current might be the key to a better cup of coffee
电流或许是冲泡出一杯好咖啡的关键
University of Oregon chemist Christopher Hendon loves his coffee—so much so that studying all the factors that go into creating the perfect cuppa constitutes a significant area of research for him. His latest project: discovering a novel means of measuring the flavor profile of coffee simply by sending an electrical current through a sample beverage. The results appear in a new paper published in the journal Nature Communications.
俄勒冈大学的化学家克里斯托弗·亨登（Christopher Hendon）非常热爱咖啡，以至于研究冲泡出一杯完美咖啡的所有影响因素，已成为他重要的研究领域。他最新的项目是：发现一种测量咖啡风味特征的新方法，只需向咖啡样本中通入电流即可。研究结果发表在《自然-通讯》（Nature Communications）杂志上。
We’ve been following Hendon’s work for several years now. For instance, in 2020, Hendon’s lab helped devise a mathematical model for brewing the perfect cup of espresso, over and over, while minimizing waste. The flavors in espresso derive from roughly 2,000 different compounds that are extracted from the coffee grounds during brewing. So it can be challenging for baristas to reproduce the same perfect cup over and over again. That’s why Hendon and his colleagues built their model for a more easily measurable property known as the extraction yield (EY): the fraction of coffee that dissolves into the final beverage. That, in turn, depends on controlling water flow and pressure as the liquid percolates through the coffee grounds. The model is based on how lithium ions propagate through a battery’s electrodes, similar to how caffeine molecules dissolve from coffee grounds.
我们关注亨登的工作已经好几年了。例如，2020年，亨登的实验室协助建立了一个数学模型，旨在反复冲泡出完美的意式浓缩咖啡，同时最大限度地减少浪费。意式浓缩咖啡的风味源于冲泡过程中从咖啡粉中提取的约2000种不同化合物。因此，咖啡师想要反复重现同样完美的一杯咖啡极具挑战性。这就是为什么亨登和他的同事们建立了一个模型，用于测量一种更容易量化的属性——萃取率（EY），即溶解在最终饮品中的咖啡成分比例。这反过来又取决于在液体渗透咖啡粉时对水流和压力的控制。该模型基于锂离子在电池电极中的传播方式，这与咖啡因分子从咖啡粉中溶解的过程非常相似。
Three years later, Hendon’s team turned their attention to studying why the microscopic clumps form in the first place, particularly at very fine grind levels. The culprit is static electricity arising from the fracturing and friction between the beans during grinding. Hendon thought reducing that static would be a good way to eliminate those clumps. The technical term is triboelectricity, which arises from the accumulation of opposite electric charges on the surfaces of two different materials due to contact with each other. A similar charge build-up also occurs during volcanic eruptions. So Hendon collaborated with volcanologists Josef Dufek and Joshua Méndez Harper, who were regulars at the same local coffee house and had noted striking similarities between the science of coffee and plumes of volcanic ash, magma, and water.
三年后，亨登的团队将注意力转向研究微小结块形成的原因，特别是在极细研磨程度下。罪魁祸首是研磨过程中咖啡豆破碎和摩擦产生的静电。亨登认为，减少静电是消除这些结块的好方法。其专业术语是“摩擦起电”（triboelectricity），即两种不同材料因接触而在表面积累相反电荷的现象。火山喷发时也会出现类似的电荷积累。因此，亨登与火山学家约瑟夫·杜费克（Josef Dufek）和约书亚·门德斯·哈珀（Joshua Méndez Harper）展开了合作，他们是同一家当地咖啡馆的常客，并注意到了咖啡科学与火山灰、岩浆和水蒸气柱之间的惊人相似之处。
Their experiments confirmed that adding a single squirt of water to coffee beans before grinding can significantly reduce the static electric charge on the resulting grounds. This, in turn, reduces clumping during brewing, yielding less waste and the strong, consistent flow needed to produce a tasty cup of espresso. Good baristas already employ the water trick; it’s known as the Ross droplet technique. But this was the first time scientists had rigorously tested that well-known hack and measured the actual charge on different types of coffee.
他们的实验证实，在研磨前向咖啡豆喷洒少量水，可以显著降低研磨后咖啡粉上的静电荷。这反过来减少了冲泡过程中的结块，减少了浪费，并提供了冲泡美味意式浓缩咖啡所需的强劲且稳定的水流。优秀的咖啡师已经在运用这种喷水技巧，即所谓的“罗斯水滴法”（Ross droplet technique）。但这是科学家们首次对这一广为人知的技巧进行严谨测试，并测量了不同类型咖啡上的实际电荷。
New use for a common tool
常见工具的新用途
There are existing methods for collecting information on coffee’s chemical composition, most notably liquid or gas chromatography combined with mass spectrometry. But these kinds of analyses are expensive and time-consuming, and predictive results are limited. There are also electrochemical techniques for measuring the concentration of caffeine and other molecules, but these have not taken into account coffee strength—a property determined by all the variables that go into preparing a cup of coffee, such as coffee and water masses, grind settings, water temperature and pressure, roast color, and so forth. That’s the information likely to be most helpful to baristas.
目前已有收集咖啡化学成分信息的方法，最著名的是液相或气相色谱法结合质谱法。但这些分析方法既昂贵又耗时，且预测结果有限。此外，还有用于测量咖啡因和其他分子浓度的电化学技术，但这些技术并未考虑“咖啡浓度”——这一属性由冲泡咖啡时的所有变量决定，例如咖啡粉和水的质量、研磨设置、水温和压力、烘焙程度等。而这些信息对咖啡师来说最为有用。
The coffee industry typically uses a method for measuring the refractive index of coffee—i.e., how light bends as it travels through the liquid—to determine strength, but it doesn’t capture the contribution of roast color to the overall flavor profile. So for this latest study, Hendon decided to focus on roast color and beverage strength, the two variables most likely to affect the sensory profile of the final cuppa. His solution turned out to be quite simple. Hendon repurposed an electrochemical tool called a potentiostat, typically used to test battery and fuel cell performance. Hendon used the tool to measure how electricity interacted with the liquid. He found that this provided a better measurement of the flavor profile. He even tested it on four different samples of coffee beans and successfully identified the distinctive signature of a batch that had failed the roaster’s quality-control process.
咖啡行业通常使用测量咖啡折射率的方法（即光线穿过液体时的弯曲程度）来确定浓度，但这无法捕捉到烘焙程度对整体风味特征的影响。因此，在最新的研究中，亨登决定专注于烘焙程度和饮品浓度，这两个变量最有可能影响最终咖啡的感官特征。他的解决方案非常简单：亨登重新利用了一种名为“恒电位仪”（potentiostat）的电化学工具，该工具通常用于测试电池和燃料电池的性能。亨登利用该工具测量了电流与液体的相互作用方式。他发现，这能提供更好的风味特征测量结果。他甚至在四种不同的咖啡豆样本上进行了测试，并成功识别出了一批未通过烘焙商质量控制流程的咖啡豆的独特特征。
Granted, one’s taste in coffee is fairly subjective, so Hendon’s goal was not to achieve a “perfect” cup but to give baristas a simple tool to consistently reproduce flavor profiles more tailored to a given customer’s taste. “It’s an objective way to make a statement about what people like in a cup of coffee,” said Hendon. “The reason you have an enjoyable cup of coffee is almost certainly that you have selected a coffee of a particular roast color and extracted it to a desired strength. Until now, we haven’t been able to separate those variables. Now we can diagnose what gives rise to that delicious cup.”
诚然，个人对咖啡的口味偏好相当主观，因此亨登的目标并非冲泡出一杯“完美”的咖啡，而是为咖啡师提供一种简单的工具，以便持续重现更符合特定顾客口味的风味特征。“这是一种客观的方式，可以说明人们喜欢什么样的咖啡，”亨登说。“你之所以能喝到一杯令人愉悦的咖啡，几乎可以肯定是因为你选择了特定烘焙程度的咖啡，并将其萃取到了理想的浓度。在此之前，我们无法将这些变量分离开来。现在，我们可以诊断出是什么造就了那杯美味的咖啡。”