How do I cure and test high curcumin turmeric to sell to oleoresin buyers?

To sell at a premium you need both good processing and proof of curcumin. After harvest, boil or steam the rhizomes until soft and the raw smell goes, then dry them fully in the sun over many days until they snap hard, then polish to remove the rough skin for a bright surface. Curing affects appearance and colour, but curcumin is mostly set by the variety and growing conditions, so do not expect curing alone to raise it much. Get a sample tested for curcumin at an accredited lab or through your buyer, because oleoresin and export buyers pay on the tested curcumin percentage. A clean, well dried, polished lot with a credible curcumin test report is what unlocks the premium price over the ordinary mandi rate.