Researchers have genetically modified coffee seedlings to produce up to 70 per cent less caffeine.

The team says demand for decaffeinated coffee is growing worldwide. Caffeine can trigger palpitations, increase blood pressure and disrupt sleep in sensitive people.

Shinjiro Ogita and colleagues at the Nara Institute of Science and Technology in Japan used a tool called RNA interference to genetically engineer the one-year-old plants.

Coffee plant cells make caffeine in a three-step process. The technique silenced an enzyme for the second step.

"At present, coffee is decaffeinated industrially, but the process is expensive and the flavour of the product is poor – problems that could potentially be overcome by the genetic engineering of coffee plants," the researchers wrote in Thursday's issue of the journal Nature.

The taste verdict won't be in until the plants mature in three to four years. The commercial definition of decaffeinated coffee in the U.S. is 97 per cent less caffeine, but geneticists haven't yet attained that level.

The Japanese team used the robusta variety of coffee plant. Other researchers are trying genetic engineering techniques on the more commercial but slower growing arabica plant.