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Vipaka is the Ayurvedic concept of the post-digestive transformation of a substance. It is the change that occurs after the action of digestive fire, which determines the substance’s later effects on the dosha, tissues and excreta. Charaka recognises three vipaka, madhura (sweet), amla (sour) and katu (pungent), which generally follow taste but with important exceptions, such as ginger, which is pungent in taste but sweet in vipaka. It has been difficult to study because it is inferred from outcomes. This review proposes that gut microbial biotransformation of phytoconstituents provides a framework for making vipaka testable. Gut microbes metabolise a wide range of plant compounds, including glycosides, polyphenols and alkaloids, into metabolites that may be more or less active than the parent compounds. The ellagitannins abundant in Triphala, for example, are converted by gut bacteria into urolithins. The capacity to produce them varies between people, and an analysis of urolithin metabotypes found that it depends mainly on age. In fermentation studies with human faeces, Triphala, liquorice and slippery elm each produced distinct microbial communities and increased short-chain fatty acid producers. In a colon simulation model, Triphala increased Akkermansia muciniphila, reduced Bifidobacterium and altered microbial metabolites. These findings parallel classical descriptions of vipaka in three ways: transformation after digestion, dependence on the individual’s digestive capacity, and effects that differ from those predicted by taste. We formulate specific hypotheses and propose study designs to test whether classical vipaka predicts microbial metabolite profiles and their physiological effects.