When coffee lovers debate the optimal brewthe argument often focuses on the relationship between roasting strategies and caffeine levels. But after a recent round of lab tests, researchers believe they’ve identified the mix of factors that make up the perfect balance of cup flavor and spiciness — and die-hard dark roast fans may want to finish taking a sip before discovering the results.
“Over 20 years ago, I heard a barista claim that dark roasts contained more caffeine, but a decade later I was exposed to the contrasting idea that light roasts were the king of caffeine. Yet I found no convincing data,” Zachary Lindsey, assistant professor of physics at Berry College in Georgia, said in a statement.
Lindsey’s team recently analyzed the relationship between the chemical and physical properties of coffee beans across various roasting and brewing scenarios. While their trial focused only on natural, washed processed Ethiopian beans, the researchers examined five varieties of roasts for brew times of one, two, and ten minutes using a coffee machine with a water/coffee ratio of 15:1.
“When selecting an infusion method, the primary goal was to implement a procedure that could consistently produce infusions across a wide range of extraction yields by only varying the infusion time “Lindsey said.
The results, published in the journal Scientific reportsoffer a detailed look at 30 unique coffee combinations at the microscopic and chemical levels. Lindsey and colleagues used high-performance liquid chromatography (HPLC) to assess the molecular composition of soluble compounds like caffeine and chlorogenic acids. In this process, compounds in an infusion are separated based on their interactions with a standard material to measure concentration. Scanning electron microscopy (SEM) photographed whole and ground beans to allow observers to closely examine the porosity and size of the beans, better highlighting the physical impact of roasting on coffee.
For the third and final tool, the team turned to refractometry, the measurement of the bending of light, to learn brewing extraction yields. According to the study, attributes such as caffeine content are the result of complex relationships between how coffee is roasted and the ability of its organic compounds to dissolve in water.
As Lindsey explains: “During roasting, the volume and porosity of the coffee beans increases as the roast progresses, making it easier for compounds to enter or exit the system. »
For example, porosity, or the measure of empty space in a coffee grounds, increases due to longer grind times. This means that more of the inner surface of each coffee grounds is exposed to water. But when it comes to caffeine, light and medium roasts on average measured higher levels than darker variants across samples across the roast spectrum. Lindsey’s team explained that this is due to the amount of caffeine lost during the process. Darker roasts, however, maintained higher caffeine levels than lighter roasts when porosity and extraction yields were uniform across all varieties.
“Although the interaction between roast degree and caffeine content has been addressed more than 20 times in the literature, the prevailing theory is that caffeine remains stable during the roasting process,” says Lindsey. “However, we establish a clear relationship between the degree of roasting, caffeine content and extraction yield.”
Like most preferences, your ideal coffee brew is ultimately a matter of personal taste (or access to ultrasonic frequencies). But if your main goal at the end of the day is to get a much-needed energy boost, Lindsey suggests a medium roast blend for the highest amount of caffeine per cup.
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