The researchers looked into the microbial communities inherent in Pu-erh tea, a special blend originating from Yunnan, China. The fresh leaves of the tea plant, Camellia sinensis, undergo two types of fermentation- the traditional raw fermentation and the faster, ripened variant. Using high-throughput rDNA-amplicon sequencing, a method to identify and quantify various bacteria and fungi present, they examined both the leaves and both types of Pu-erh tea. The study also explored possible mycotoxins in the tea profiles through quantitative liquid chromatography-tandem mass spectrometry, a technique used to detect and quantify various substances.

Despite observing significant alterations in the fungal and bacterial compositions due to both fermentation processes, the researchers found the aging process to produce noteworthy changes in raw Pu-erh but not in the ripened type. They identified 390 fungal operational taxonomic units (OTUs) and 629 bacterial OTUs in the leaves and teas. Interestingly, despite the difference in the speed and nature of the fermentation processes, ripened and well-aged raw Pu-erh teas exhibited similar microbial communities alien from those observed in young, raw Ph-erh tea. They also found 25 toxic metabolites, primarily of fungal origin, with the most common being patulin and asperglaucide. These facts lend credibility to the Chinese custom of discarding the first preparation of the Pu-erh tea and using the damp tea for subsequent brewing.