(THE JAKARTA POST/ASIA NEWS NETWORK) - Sumatran coffee is said to be the most popular single-origin coffee at Starbucks.

In fact, the Sumatra blend is not only popular among Starbucks' customers. Mr Howard Schultz, founder of Starbucks, is also a fan of Sumatran coffee.

In a letter announcing his resignation, he wrote: "I write to you today enjoying a french press of my favourite coffee, aged Sumatra, and I am feeling so many emotions."

Here comes the question: What made the founder of the world's largest coffee chain fall in love with Sumatran coffee?

Mr Surip Mawardi, an agronomist at the Starbucks Farmer Support Center, told The Jakarta Post that Sumatran coffee has several specific characteristics, namely full-bodied, complex flavour and a long aftertaste, making it loved by many.

These characteristics are due to two factors: geographical conditions and people.

Mr Surip said Sumatra has fertile volcanic soil and high rainfall. Although Java has volcanic soil, its rainfall is considerably lower than in Sumatra.

With regards to the people, he said Sumatran farmers have a unique way of processing coffee. Known as semi-washed, the coffee is wet-hulled, resulting in a complex flavour.

"Coffee from other countries usually uses full-washed processing," he said, explaining why Sumatran coffee has a one of a kind flavour.