Chemistry in Your Coffee Cup

Reports abound about the health effects of coffee, depicting it as everything from a dangerous drug to an elixir of life, and a recent study adds further uncertainty to the mix. Scientists at the University of Glasgow have recently quantified what coffee aficionados have always insisted: not every espresso is created equal.

The researchers visited 20 shops in Glasgow’s west end, ordering a single espresso in each. They opted for take-away and brought their coffees back to the lab for analysis by high performance liquid chromatography, a technique for separating the individual components of a chemical mixture. With this approach, they measured levels of chlorogenic acids, a set of antioxidant compounds whose effects on us remain unclear, and caffeine.

The results showed huge variation in the chemical content of the coffees, with some containing up to six times more caffeine than others. Even taking into account differences in serving size, some still had three times more caffeine per unit volume. Notably, every single coffee analysed contained more than the 50mg of caffeine often cited as standard for a single espresso shot.

Why the variability? Multiple factors affect coffee’s chemical content, such as whether the beans come from arabica or robusta plants (arabica beans have less caffeine) and the extent of roasting, which breaks down caffeine. The grind’s fineness and the pressure and temperature settings on the espresso machine also affect the final result.

This variability means you could unwitting swallow more caffeine than you intend. Variations in sensitivity from one person to the next mean there is no daily allowance suitable for everyone, but the Glasgow researchers suggest that customers would benefit from information about the contents of their beverages.

On a practical note, supposing you find yourself thirsting for coffee in Glasgow, Beanscene and Starbucks will soothe you with just under 2mg of caffeine per millilitre of espresso (coming out to just 51mg for the smaller Starbucks shot and 77mg for Beanscene’s larger one). Costa Coffee and Heart Buchanan pack the biggest punches, each with more than 6mg of caffeine per millilitre.

Author - Catie Lichten

Update - Mark Lear - 2014

This study was recently published in the Royal Society of Chemistry's journal Food and Function in 2011