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Recently many of your Have probably heard that turmeric powder has been found to be contaminated by lead. This is true, and has lead California to ban important turmeric which is not properly labeled with lead labels. While some people may say that this is just another protectionist gimmick to create a market for California Farmers. However, numerous tests, including tests by us, have shown that there is lead in turmeric powder, above safe levels. In fact much of the world's turmeric powder is contaminated with lead -- so much so that you should ask for lab reports before purchasing turmeric powder from a supplier.
However, most research on the subject cannot find a source of the lead. At roosterfarms, we did three tests where one turmeric was ground with a standard flour grinder, another turmeric was ground with a ceramic ball mill, and a third was ground with a kitchen aid grinder. The flour grinder showed lead levels above acceptable levels, while the kitchen aid grinder only contained lead below the acceptable levels for california. however, the ceramic ball mill grinder showed lead levels below the detectable limit. This anecdotal study leads us to believe that the lead in the world turmeric supply is not caused by contaiminated soil, but rather is due to the processing of turmeric. Naturally, some soils will contain lead, however most turmeric should not show high levels of lead, if they are grown in disparate regions of the world. The levels of lead are surprisingly similar despite the location where the turmeric is grown. Thus, it is unlikely that the soil is the source of turmeric lead poison.
The idea that the soil was the source of the originated after lead was found in turmeric which was grown in Bangladesh after heavy rains. Lead chromate was detected in turmeric, and immediately people were saying that lead chromate was added to the powder for coloring. Interestingly, the other contaiminated turmeric are all in powder form and not in the fresh form. However, if we examine the evidence further, it seems that the heavy rains which caused the turmeric to look pale, was actually lowering the pH of the flood planes, which tend to have calciferous high pH soil. Incidentally, this is also the soil where turmeric was being grown. Turmeric is a color indicator, and gets lighter or darker depending on the pH. Thus, the rains lowered the pH of the soil resulting in a paler crop. While the curcumin levels are likely the same, the association of yellow with health lead some processors to add lead chromate into their spices.
However, most lead contamination comes from the grinding process. By using a ball mill instead of a flour mill, we are using ceramic to grind the turmeric, rather than grinding the turmeric against metal. Most metals have lead adulteration in it, and since lead is the softest of the metals, it will leach into the turmeric powder first.