The Difference Between Fermentation in Tea and Fermented Foods

Black tea and oolong tea are often categorized as "fermented teas," but the extent to which they undergo fermentation raises questions about whether they truly qualify as fermented foods. In this article, I endeavour to offer a thorough exploration of the distinctions between tea and traditional fermented foods, shedding light on the nuances of their processing methods and biochemical transformations.

Common Fermented Foods

When we talk about fermented foods, we're referring to foods where microorganisms play a pivotal role in the production process. Representative examples of fermented foods include alcoholic beverages, miso, soy sauce, cheese, natto, yogurt, and more. During the production of fermented foods, microorganisms consume food components, multiply, and simultaneously transform these components into distinct organic compounds through enzymes derived from microorganisms. Essentially, the term "fermentation" in the context of fermented foods signifies the enzymatic conversion of the food's components facilitated by enzymes derived from microorganisms.

The Fermentation Process in Tea

Tea is often broadly categorized as a fermented food, but when it comes to teas like black tea and oolong tea, there is no involvement of microorganisms in the "fermentation" process. This sets the fermentation process of tea apart from that of other fermented foods. In the case of tea fermentation, the polyphenols and other components present in the tea leaves are transformed by the naturally occurring enzymes in the tea leaves. Initially, these enzymes and polyphenols are stored separately within the cells. However, through the process of rolling or kneading, the cells are damaged, allowing the enzymes and polyphenols to mix and initiate a reaction. In tea, fermentation primarily involves enzymatic reactions facilitated by the plant's own enzymes and components, such as polyphenols. This distinctive process distinguishes tea fermentation from the fermentation processes observed in other fermented foods. In summary, the fermentation process observed in typical fermented foods involves enzymatic reactions facilitated by microorganisms. However, in the case of tea, fermentation entails a transformation of components through the inherent enzymatic reactions present within the tea itself. While the Chinese character "酵" in fermentation signifies enzymes, and tea indeed utilizes enzymes in its processing, it deviates significantly from what is conventionally considered fermented foods due to the absence of microbial involvement.

Other Foods Utilizing Enzymatic Reactions Similar to Tea

Numerous other types of enzymatic reactions, akin to those observed in tea, can be found in various foods. For instance, the formation of pungent components and the generation of aroma in garlic and onions also follow a similar mechanism. The characteristic smell of plants in the Allium family, such as onions, arises when the cells are disrupted through cutting, facilitating the mixing of enzymes and substrates. Grating wasabi triggers a enzymatic reaction that results in the formation of spiciness, akin to the fermentation process observed in black tea. Within the cells of wasabi, an enzyme called myrosinase coexists with a component called sinigrin glucoside. When grated, the cells rupture, allowing these two substances to combine and produce the pungent compound allyl isothiocyanate. Interestingly, wasabi itself has a sweet and mildly bitter taste. Similarly, the transformation of green peppercorns into black pepper shares a related process, as does the browning of apples or bananas when cut, all involving enzymatic reactions. The enzymatic reactions observed in these foods mirror those found in the fermentation process of tea. However, neither plants from the Allium family, such as onions, nor wasabi are categorized as fermented foods. Hence, referring to tea as a fermented food is rather exceptional within the scope of food classification.

Exceptional Tea Made Through Microbial Fermentation

Certain teas, such as Pu-erh and some dark teas, undergo fermentation involving microorganisms, similar to typical fermented foods. For instance, Pu-erh ripe tea is produced through the fermentation of microorganisms such as bacteria, yeast, and mold. Unlike the traditional fermentation process of tea leaves, the raw material, Pu-erh raw tea, undergoes a heating process during production, which deactivates the enzymes. Consequently, the distinct flavor of ripe tea is primarily created by microorganisms and their enzymes, rather than those derived from the tea leaves themselves.