How is turmeric powder adulterated?
There are two common ways to do so:
Adding fillers, which may or may not have any nutritional value or may actually end up harming you in long term. Some common fillers are saw dust, rice flour, starch, etc.
Use of Color dyes to give the traditional turmeric color to added fillers. The use of metanil yellow colour and lead chromate are most common. The use of color is common in countries like India. Thus is unfortunate as India is largest producer, consumer and exporter of turmeric in the world. This is known to negatively impact nervous system of body and may cause cancer according to some experts.
But fortunately there are some ways to find the difference. Let’s discuss them.
How to identify genuine turmeric powder
My mother can differentiate between an adulterated one and genuine by looking, smelling, rubbing, tasting, etc. But it is hard to describe that process as it is based on experience and not exact science. It confuses me a lot 
But there are some other more scientific ways to do tests too. Here they are
Turmeric artificial color test
Here is the test for artificial colors in turmeric.
Test 1: For Metanil Yellow
Take one teaspoon of turmeric powder in a test tube / glass flask. Then add few drops of concentrated Hydrocholric acid (HCL) in it.
If pink color appears instantly but then disappears after adding some water turmer
does not have the artificial 
color. But if the color remains, it has artificial color — metanil yellow.
Note: a few people over internet have mentioned that one can also use lemon instead of HCL, but I cannot confirm that.
Test 2: For Lead Chromate
This one is a bit difficult than the first one. Take sample of turmeric. Ash the sample. Collect the ash in a flask / test tube and add 1:7 Sulphuric acid to it.
Mix the sample and then filter it into another beaker / flask (basically the ash will remain in the filter while liquid will come down).
Next add a few drops (1 or 2) of 0.1% dipenylcarbazide into the solution. If it turns pink it has Lead chromate.
Turmeric chalk powder test
Take small amount of turmeric. Add it into a test tube / glass flask. Add some water.
Then add a few drops of concentrated HCL to it. If you witness effervescence then there is chalk powder present in turmeric.
This test is also applicable for testing turmeric for yellow soapstone.
Microscope test for starch in turmeric powder
Starch of rice, maize, wheat etc. are also added to turmeric powder.
Under a microscope Turmeric looks like big, yellow and angular particles. While the added starch particles are small and colorless.
Water test for chalk powder in turmeric
This is easiest of all test and can be done quickly to find if there is chalk powder added to your turmeric. Here it is:
Take some warm water in a clear glass and then drop 1 teaspoon of turmeric powder on its surface. Just put it and let it do its job – do not stir.
Soon you will see chunks of turmeric powder settling at the bottom of the glass. Then lots of sediments settling too, making the water cloudy.
Check after 20 min, if you see sediment at bottom but the water is clear yellow (not cloudy). Then there is no chalk powder in the turmeric.
If the water looks cloudy (means you cannot see through the glass clearly), then there maybe chalk added to the powder.
I do not have HCL nor Sulphuric Acid – what should I do?
While one can do the chalk test but it is the artificial colors present one should be more worried about. How do you check them as rarely people will have access to  HCl or Sulphuric acid.
This is a good question. As even I do not have these chemicals to test my turmeric. But there are a few things we can still do:
If you buy in bulk
Ask your supplier to get these tests done for you, if possible in front of you and from a random sample.
Even if you cannot get it done in front of you, I am sure just asking for a test report will ensure they give good quality stuff to you. As the report can be used as an evidence against them in court of law if adulteration is found later.
If you buy in small quantities
Go for brands which are independently certified for quality. I am saying this as every brand says they are the best. But having an independent certification of quality helps.
Some such certifications are:
- Safe Quality Food (SQF)
- Hazards and Critical Control Points (HACCP) – issued by WHO
- Good Manufacturing Practices (GMP)
- International Organization for Standardization (ISO) 9001:2000
- Orthodox Union (OU) Kosher
- International organic certifications such as: USDA, EU, and NSOP (India)
Do these tests apply for supplements?
I am not sure as supplements may contain additional ingredients  and thus they may interfere with the above mentioned tests.
But most of the quality certifications mentioned above should still be valid. So you should consider that method to chose a good quality supplement.
In the end..
Turmeric is miracle of nature but we have to be really careful to ensure we are taking its pure form and not adulterated. Such products can do more harm than good. So be vigilant.
