What is “Wet Piling” (Wo Dui)?

Traditional sheng pu erh tea can take years to age, before it developed this smooth and sweet flavour that tea lovers longed for. Yet, this wasn’t at all an issue in the early days. Men and horses transported the cakes by foot along the ancient tea horse road to neighbouring countries. Such journey’s where long, allowing the teas to properly age while they were on the way to their destination. In addition, the tea houses in Hong Kong and Guangdong stored lots of pu erh so that they could age many years before they were served to customers.

However, as transportation improved and demand increased, slowly it was obvious that there was a scarcity of properly aged pu erh. Mankind, therefore invented the ‘wet piling’ or ‘wet storage’ method.

Wet piling, in China known as ‘wo dui’ (渥堆). It’s a fermentation process used for the production of shou pu erh. It was first developed in 1972 by Kunming Tea Factory. This technique manipulates conditions to accelerate the pu erh aging process by prolonged bacterial and fungal fermentation under a controlled warm humid environment.

Sheng & Shou Pu Erh

To understand this method, we first need to understand the differences between a traditional sheng (raw) pu erh and shou (ripe) pu erh.

A traditional sheng pu erh was picked, roasted, sun dried, and at last steamed for compression into round discs. The problem is that afterwards it needs at least 3-5 years of aging until the taste transforms from astringent to smooth, and from bitter to sweet.

The development of the wet storage process was intended to shorten this aging period. Because of this brilliant invention, the long fermentation period was shortened to just 45 days. With the discovery of the wet storage method, leaves are now first post-fermentation before they are compressed into cakes, resulting in: shou pu erh.

Initially, ‘wo dui’ was ment to imitate the flavour and colour of an aged sheng pu-erh. However, due to the significant different taste profile, its more often regarded as a new style of pu erh.

How Does Wet Piling Work?

To apply the wet piling method, one first needs ‘mao cha’ which literally is ‘unfinished tea’. This mao cha is the result of picking, pan firing, rolling and sun-drying leaves. As said before, Mao cha is then compressed into sheng pu erh cakes, or wet stored to create shou pu erh. We discuss the wet storage steps below.

The process of wet piling involves piling, wetting, and turning the tea leaves which is similar to composting:

• Piling: pile the mao cha leaves to certain height. This usually around 70 cm, but individual tea masters have their own preferences.
• Wetting/dampening: wet the piles of mao cha with water, and cover them with a linen cloth. This step allows the mao cha to stay in a warm and humid environment in order to accelerate the fermentation.
• Turning: wait until the piles of tea ferment to certain degree, spread it out and let them air.

Depending on the different degrees of wet piling, mao cha can turn from green to yellow, maroon, or brownish black colour. You can tell the wet piling degree from the colour of the liquor – the darker the liquor gets, the higher the wet piling degree is, and vice versa.