Revisiting the Caffeine and Roast Level Debate

Revisiting the Caffeine and Roast Level Debate 

This time, with Science! 

A few years ago I weighed in on the Royal blog on caffeine in coffee, and its relationship to roast degree. I’m pleased to say that some very smart folks at Berry College and Drexel University have published a paper in Scientific Reports recently that sets the record straight, and I’m thrilled that Royal Coffee proudly contributed coffee to the research. 

Summary of Results 

Let’s cut to the chase. The study found that: 

1. If brewing conditions are identical (i.e., dose, water ratio, etc.), then lighter roasts have more caffeine in the resulting brew. 
2. If the extraction percentage of the brew is identical, then a coffee brewed with darker roasts has more caffeine. 

Why? 

The study posits that “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.” 

That is to say, it’s complicated. As I tell folks who ask me these days, if you’re looking to increase the caffeine level in a cup of coffee, there are more efficient ways to do so than by controlling for roast degree. Two easy suggestions might include either (a) using a higher dose of coffee, or (b) switching to Robusta. 

Study Methodology 

Prof. Zachary Lindsey, et al., used two green coffees from Ethiopia, supplied by Royal Coffee and chosen specifically for their different responses to heat in the roaster. 

The coffee was roasted on an Aillio Bullet to five different roast degrees. Roasts were degassed for ten days, ground and sieved (to control for grind particle size), and brewed using an Aeropress and mineralized water at a ratio of fifteen parts water to one part coffee to controlled brew times (one, two, and ten minutes in duration), and using a mechanized “brewer stack” to ensure consistent extraction methods. Extraction percentage was calculated with the aid of a VST refractometer, and caffeine (as well as chlorogenic acids or CGAs) were measured through liquid chromatography. Using this method, the study was able to use CGA concentrations as a proxy for roast degree (since CGAs degrade during roasting). 

Interesting Findings 

The study observed that “extraction yields were generally observed to decrease with increasing degree of roast,” which reinforces a long-held theory I’ve held, and some casual experimentation I’d run a number of years ago. 

Basically, there’s more extractable stuff in lighter roasts – more soluble material. However, darker roasts, the study found, are more porous, which they theorize affects both sublimation (caffeine burnoff during roasting) and extraction. 

They found suggestions in their research that “caffeine did indeed leave the coffee seeds during roasting… but… sublimation effects did not become significant until the bean probe temperature exceeded values of approximately 400–420F.” 

The conclusion the team came to is that while there’s less caffeine present in darker roasted beans, it represents a “greater fraction of the remaining extractable material,” and that “extraction yield seems to play a more impactful role on resulting caffeine content in brewed coffee than the degree of roast alone.” 

It’s exciting to see more and more of this kind of work taken seriously in academia; and it has been rewarding to contribute to its completion. We’re looking forward to more great work in coffee science!