Here is an infamous example of adulteration of spices.
In 2005 an effort by some unscrupulous spice producers in India to cheapen their processed spices led to the largest food product recall in the world.
These producers were adulterating their red chilli powders by bulking them up with stems, mouldy pods, seeds and ghost pods (light coloured pods where the pigments have not developed). The problem was that by doing this, the chilli powders they produced no longer had a typical red colour. The answer they came up with was to add a collection of dyes generally referred to as Sudan Red (Sudan 1, 11, 111 and 1V). The results were chilli powders with a more authentic colour. Sudan Red dyes are commonly used in India to dye leather and fabric. The European Food Safety Authority considers Sudan Red to be genotoxic and carcinogenic; that’s why it is banned.
The reason these unethical producers went to all this trouble is because they ended up with faux red chilli powders that they could sell for less than cost of corresponding whole red chillies. In other words, it was much more profitable than producing an authentic product.
Fortunately they came unstuck. One of the producers used an excess of Sudan I, which is yellow in colour. In an effort to correct that colour, he then had to add more of the redder Sudan dyes. This ended up making the final red chilli powder look very unnatural which in turn led to the identification of the problem.
The contaminated red chilli powders were recalled and further supplies of them were cut off. However, the problem was hugely exacerbated by the use of red chilli powder as an ingredient in Worcestershire Sauce. In February 2005 it was discovered that the red chilli powders contaminated by Sudan Red had been used in the production of Worcestershire Sauce. Worcestershire Sauce is itself used as an ingredient in dozens other food products, not least ready meals. The recall of Worcestershire Sauce and other products in which it was used is the largest in history.