(CNN) The "world's strongest coffee" is now available in the US, but just one cup could spill you over the daily caffeine limit.

"If you want to stand out, you need to be the 'est' -- the biggest, smartest, strongest, or cheapest," said Black Insomnia founder Sean Kristafor. "So when we wanted to compete in coffee, as a caffeine product, we had to be the strongest, but obviously, we don't exceed the world guidelines."

Black Insomnia

As a coffee aficionado, Kristafor created the company after retiring from a corporate job. He found a top coffee roaster online and created Black Insomnia last June, first selling locally to cafes in Cape Town, South Africa.

Retailing at $19 a pound, the company's online business sold three tons more than the other local shops in August, he said. By October, they had customers in 22 countries. And by March, they were listed on Amazon in the US. Now, the company says it sells five to six tons of coffee a month.

With a sweet nutty taste, Black Insomnia's strength comes from the type of bean, robusta, and the way they are roasted. To prove their "world's strongest" title, Kristafor had his beans tested chemically against competitors.

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