You may wonder how one chooses the right trees for removal. Here we touch upon the collaboration between laboratory work and field work. It is this collaboration that made the quinine culture so powerful. It enabled careful decision making in the field based on laboratory research and analysis. These methods have been perfected at the Tjinjiroean Plantation.

The trees are marked with orange paint, clearly visible on a brown bark. At the point of the mark the trees are measured twice a year. Above the mark a small hole is made in the bark of exactly 1cm². This little piece of bark is then analysed carefully to assess the exact quinine content. The content can then be compared between trees and the right trees can be chosen for harvesting.