Dark tea is one of China's six major tea categories, with a history of over 400 years. It is unique to China and serves as an essential daily beverage for domestic ethnic minorities. Dark tea products are diverse and come in various shapes, divided into compressed tea and loose tea categories. Compressed tea includes Fu brick, Hei brick, Qing brick, Kang brick, Jinjian, and Fangbao, while loose tea includes Tianjian, Gongjian, Shengjian, and Liupao tea. Dark tea is now primarily represented by Hunan Anhua dark tea, with Hunan dark tea mainly supplied to border regions.

"Pile fermentation" is both a distinctive process that differentiates dark tea from other tea categories and a crucial process in forming dark tea's quality. The enzyme activity during pile fermentation involves the simple reactivation of endogenous enzymes from fresh leaves. It is believed that the essence of dark tea pile fermentation is the oxidation and condensation of polyphenolic compounds under the action of residual enzymes. Corresponding to the "fermentation" of black tea, some people in the past referred to dark tea pile fermentation as "post-fermentation" for this reason. Enzymes are special proteins with catalytic ability, produced by living cells in organisms. Enzymes are essential substances for metabolism in living organisms. Without enzymes, there would be no metabolism and no life.

The chemical nature of enzymes is protein, which reactivates as temperature increases and proteins denature. Enzymes themselves are divided into two types: simple proteins and conjugated proteins. Enzymes whose structure consists solely of simple proteins have activity determined by the protein structure; these are called simple enzymes, such as amylase and protease among hydrolases. Another type of enzyme contains both protein and non-protein components in its structure, and enzyme activity only occurs when these two parts combine; these are called conjugated enzymes. Most oxidases belong to conjugated enzymes.

Enzymes discovered during the dark tea pile fermentation process include polyphenol oxidase, peroxidase, cellulase, pectinase, and protease. These enzymes are quite abundant during the post-fermentation process. Their exact quantities cannot currently be calculated.

This determines the multi-enzyme quality of dark tea. Recent research has confirmed that the multiple enzymes in dark tea can enhance the binding capacity of insulin receptors, a function not present in current medications.

Dark tea can digest meat, break down fats, and regulate three metabolic processes (sugar metabolism, fat metabolism, water metabolism). This is one reason why ethnic minorities in border regions who primarily consume meat rarely suffer from diabetes and prostate diseases. Mongolian medicine's belief that dark tea nourishes the kidneys is also quite reasonable.

Similar to traditional Chinese medicine chenpi, dark tea improves with age. During storage, it produces hundreds of precious enzymes that can benefit the kidneys and reduce turbidity, having positive effects on nephritis and diabetic nephropathy. Nano dark tea further enhances dark tea's inherent properties. Particularly for middle-aged and elderly people, nano dark tea can penetrate the prostate barrier, reaching deep areas of the prostate that medications cannot access, thus producing remarkable effects.

Dark tea is now becoming a popular tea variety among tea enthusiasts in various regions.