Cafe culture: how strong is your coffee?

Wake up and smell the coffee – it might give you more of a jolt than you think. Scientists at Glasgow University have analysed 20 cups of the black stuff from different coffee shops across the city – and discovered that some had six times the level of caffeine than others.

It’s widely assumed that an average espresso contains around 50mg of caffeine – and the Food Standards Agency has advised pregnant women not to consume more than 200mg a day – as an excess has been linked to an increased risk of miscarriage, or low birth weight. But if you assume that means you can glug back 4 espressos with gay abandon, be careful where you buy them.

Caffeined up

According to the researchers, the lowest level of caffeine was found in a Starbucks espresso – with 51mg. Four shops contained more than 200mg – with the highest level at an independent cafe, Patisserie Francoise. Cup sizes also varied, from 23ml to a much larger 70ml.

Alan Crozier, from Glasgow University’s School of Medicine, said the data was just a snap-shot – “but the range and scale of the results is sufficient to demonstrate that there is a problem, unlikely to be restricted to Glasgow.”

Artisan coffee companies say they tend to concentrate more on the flavour than the levels of caffeine in their brew – but there could be several explanations for the wide variation in commercial coffees.

Bean and gone

Agnes Potter, from the London roastery Allpress Espresso, told Channel 4 News that the naturally occuring caffeine in different plants was different, with much lower levels in Arabica coffee beans than the less refined tasting Robusta – often used in instant coffee or less specialist brews.

Caffeine is also water soluble, she said, so the longer the brew time, the more caffeine you end up with. A typical espresso takes around 22-28 seconds to make, whereas coffee sits in a cafetiere for up to four minutes, and takes between 2-3 minutes to go through a filter machine. And, she said, the grind size also makes a difference: a finer ground bean, with a larger surface area coming into contact with the water, produces a more highly-caffeinated brew.

No froth, no whip

Former world barista champion Gwilym Davies, from the cult coffee firm, Prufrock, told us that the increase in coffee prices has led to some companies using the cheaper Robusta beans to mix into their blend. Different processes also mean that some retailers may use just 7g of coffee in a typical espresso, whereas others use up to 22g. “It’s like different recipes.” he said. “What we call an espresso would be a double or triple espresso in some places”.

There’s also plenty of science to explain why caffeine levels vary naturally. Davies says it’s produced to protect the coffee plant against pests. So coffees grown on higher ground, which tend to be more prized and therefore more expensive, are lower in caffeine because there are far fewer pests in the environment.

Arabicas have a more refined flavour and tend to be used for speciality coffee. Agnes Potter, Allpress Espresso

But, he cautions, “we don’t want people to buy coffee based on the caffeine – we’d rather they chose it because of the flavour, not just the jolt.”

Daily grind

Whatever the wake-up qualities, for a nation famed as tea drinkers, Britons now spend an astonishing £730 million on coffee – with each person consuming an agerage of 500g a year.

Caffeine typically stays in the body for around five hours, but it can linger as long as thirty hours for those considered more susceptible.

But Alan Crozier says there’s no need for most people to reach for the decaff. “As long as you can tolerate caffeine and do not suffer adverse side effects, and are neither pregnant, young, or have liver disease, enjoy drinking your full-bodied coffee.”