Spend any time in tech circles in Berlin and you'll come across Club Mate (pronounced mah-ta, like stigmata).
It's a plant-based energy drink, kind of like a cola, but lighter. The taste is unusual and hard to describe.
But it's strangely addictive. Once they've tried it, people tend to become somewhat obsessed.
The drink is particularly popular among developers, who find its caffeine content helps them focus.
It certainly gives you a lift - after drinking my first bottle I could feel my heart pound, and I'm big coffee drinker with a high caffeine tolerance.
A half-litre bottle contains 100mg of caffeine, which is about twice as much as a can of Diet Coke, and slightly more than a 250ml can of Red Bull.
So it's potent, but probably better for you than a lot of fizzy drinks. It contains half as many calories as Coca Cola (38 kcal / 100 g), and half as much sugar (5g vs 10.6g).
Plus, it's a decent cocktail mixer. Add rum, sugar and lime, and you've got yourself a Tschunk, a delightfully German spin on the Caipirinha.
Club Mate is just one of many drinks derived from Yerba mate, a plant that grows in South America and has been consumed there as tea for thousands of years.
Though the drink has a cult following in America, it's pretty hard to find outside Germany.
So if you want to try it, you'll most likely have to order it yourself online.
Alternatively, move to Berlin.
UPDATE
According to Kristof Partyka, who distributes the drink via Club Mate UK, 100 venues in the UK stock Club Mate. He says demand is rising - sales in the UK increased 35% in 2015 - with a strong following among students in particular. "We notice that sales of Club-Mate grow strongly before and during exams," he tells BuzzFeed.