Coffee – Difference in caffeine levels between light and bold coffee

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Over the last few years I had come to believe that the roasting process for bold coffees removed caffeine from the beans resulting in a lower caffeine content than compared to a light roasted coffee. I got this idea from Good Eats with Alton brown. Here's the clip where the master roaster makes this point.

However, yesterday's On Point w/ Tom Ashbrook had on a coffee expert that made the opposite claim. Also, comments the page have pointed to sources describing the inconsistency of caffeine levels: Caffeine content by roast level and Does dark roast coffee have less caffeine than light roast?

Searching around on .edu sites I find charts that seem to support the idea that bolder coffees contain more caffeine. The charts show smaller amounts of bold coffee (2-4oz) contain the same amount of caffeine as larger amounts of light roasted coffee (6oz). So, obviously, typical consumption amounts play a role in how much caffeine will be ingested.

Caffeine Charts

In the end, I'd like a definitive answer to this question: after roasting which bean contains more caffeine or is the difference negligible? And/or does the brewing method significantly alter the caffeine content?

Best Answer

I believe that the following study provides a definitive answer:

From the abstract:

High performance liquid chromatography (HPLC) was applied to the analysis of caffeine, trigonelline, nicotinic acid and sucrose in Arabica and Robusta coffee. Green and roasted coffee samples were used in this study and the degradation of sucrose and trigonelline, with the formation of nicotinic acid, was followed during roasting. Caffeine did not undergo significant degradation with only 5.4% being lost under severe roasting.

Roasting does in fact lower the caffeine content, so bolder coffees will have less caffeine if they come from the exact same bean. But even under the worst conditions, the impact of roasting is trivial compared to the impact of bean selection, brewing method, etc.

What does degrade is sucrose (sugar), which is why heavily-roasted beans tend to taste so bitter (or "bold").

Bottom line: Make your roasting decision based on flavour preference, not caffeine content. Because the effect on caffeine is so small, you really can't compare the caffeine content of light roasts vs. dark roasts categorically unless you have a controlled sample, which you don't unless you're working in a lab.

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