Are you sure your sampling method is correct? Perhaps the pine needles have to be prepared in some way before brewing... i.e., drying the leaves, muddling them, or treating them chemically in some other way. Just by way of a completely unrelated example, native americans treated maize with lime (the mineral, not the fruit) to liberate the vitamin niacin, a process called nixtamalization
. It is still used commercially today to produce hominy and many corn-based products derived therefrom (tortillas, pozole, grits). As pine needles are (by design) quite tough, waxy, and resistant to water, perhaps if there is truth to these stories, the pine-needles were similarly treated to enhance the concentration of extractables in the brewed product. Just speculation.