Department of Physics, Berry College, Rome, GA, USA.
Department of Chemistry, Drexel University, Philadelphia, PA, USA.
Sci Rep. 2024 Nov 25;14(1):29126. doi: 10.1038/s41598-024-80385-3.
The effect of degree of roast on resulting caffeine content in brewed coffee has been extensively researched, but conflicting methodologies and results have muddled development of a general conclusion. In this study, 30 unique combinations of green coffee variety, degree of roast, and brew time were investigated regarding extraction yield and caffeine content. An AeroPress brewer was used to prepare brew samples using a 15:1 mass ratio of brew water to ground coffee. Refractometry and HPLC were respectively used to measure extraction yield and caffeine content of brewed samples. Scanning electron microscopy was used to measure porosity of roasted seeds and showed increasing porosity with the degree of roast. Extraction yields generally decreased for roast batches with roasting mass losses greater than 12-14%, and caffeine concentrations in 10-min brews decreased for roast batches with drop temperatures greater than 400-420 F. Under identical brewing conditions, caffeine concentrations in brewed samples were generally lower for dark roasts than light and medium roasts. However, at identical extraction yields, dark roasts generally exhibited higher caffeine concentrations than lighter roasted coffees. It is likely that the volatilization or decomposition of soluble compounds and increased porosity due to roasting act as competing mechanisms that determine compound concentrations in resulting brews.
烘焙程度对冲泡咖啡中咖啡因含量的影响已经得到了广泛的研究，但由于方法学和结果的冲突，使得得出一般性结论变得复杂。在这项研究中，研究了 30 种独特的绿咖啡豆品种、烘焙程度和冲泡时间组合，以研究萃取率和咖啡因含量。使用 AeroPress 冲泡器以 15:1 的冲泡水与研磨咖啡的质量比制备冲泡样品。折射计和高效液相色谱法分别用于测量冲泡样品的萃取率和咖啡因含量。扫描电子显微镜用于测量烘焙种子的孔隙率，结果表明随着烘焙程度的增加孔隙率增加。对于烘焙质量损失大于 12-14%的批次，萃取率普遍降低，对于降温大于 400-420°F 的批次，10 分钟冲泡的咖啡因浓度降低。在相同的冲泡条件下，深色烘焙的咖啡因浓度通常低于浅色和中等烘焙。然而，在相同的萃取率下，深色烘焙通常比浅色烘焙的咖啡含有更高的咖啡因浓度。很可能是由于烘焙导致的可溶性化合物的挥发或分解以及增加的孔隙率作为竞争机制，决定了冲泡后饮料中化合物的浓度。
