You buy the same supplement twice. The first bottle tastes fine. The second tastes different — sharper, sweeter, or faintly metallic. Nothing on the label has changed, and the brand insists the formula is identical. In most cases the brand is telling the truth, and the taste changed anyway. Natural products vary, and supplements are made from natural products.

The main reason is the raw material. Herbal extracts, fish oils, fruit powders and botanical ingredients are grown, harvested and processed in different places at different times of year. A turmeric root harvested after a wet season contains a different balance of compounds from one harvested after a dry season. A fish oil pressed from a winter catch tastes different from one pressed in summer.…