Is Pu'er a Moldy Tea?
Hearing for the first time that pu'er is "fermented" and "aged," combined with ripe tea's dark color and distinctive aroma, many people think of mold. This misconception is very common, but once you lay out how pu'er is made, it's clear that it and mold are two different things.
Is Pu'er Made by Letting It Go Moldy?
No. Pu'er comes in raw and ripe:
- Raw tea (sheng): Fresh leaves are pan-fired to stop oxidation (shaqing), rolled, and sun-dried into shaiqing maocha (sun-dried rough tea), then steamed, pressed into shape, and dried. There's no step in the process that makes the tea moldy.
- Ripe tea (shou): Shaiqing maocha goes through wodui, meaning it's piled up to ferment in an environment with controlled temperature and humidity, then dried, sorted, and pressed or made into loose tea.
China's national standard for pu'er, GB/T 22111, describes ripe tea as tea that has undergone post-fermentation, and every step of the process is a clearly defined procedure.
Is Pile Fermentation the Same as Mold?
There are indeed microbes at work in the pile, including molds, and that's worth saying plainly. Researchers analyzing pile samples have found that Aspergillus niger dominates the early stage, while Bacillus, yeasts, and other microbes take over later. The pile temperature is often between 50–65°C (122–149°F), and it requires regular turning and spraying with water to control. During this process, tea polyphenols gradually decrease while theabrownins gradually increase, so the liquor becomes deep red and the taste turns mellow.
This is similar in principle to brewing soy sauce, miso, and Shaoxing wine with koji molds: under controlled conditions, specific microbes carry out specific transformations.
Mold is something completely different: tea absorbs moisture in storage, allowing molds that shouldn't be there to grow from the environment. The smell is damp and pungent, and mycelium or mold spots appear on the surface of the tea.
| Pile fermentation (wodui) | Mold | |
|---|---|---|
| Where it happens | The tea factory's fermentation room | A damp storage environment |
| Controlled? | Temperature, humidity, and turning schedule are controlled | Uncontrolled |
| Result | Deep red liquor, aged aroma, mellow taste | Moldy smell, mycelium, spots |
| Drinkable? | The finished ripe tea is drinkable | Don't drink it |
Details on wodui are in Wodui: How Ripe Pu'er Is Made and The Microbes in the Wodui Pile.
Is Raw Tea Fermented?
Raw tea doesn't go through wodui when it's made, so freshly made raw tea is closer in nature to sun-dried green tea. It transforms slowly in storage: tea polyphenols gradually decrease, pigments increase, and the aroma moves from floral and honeyed toward aged and woody notes. The tea world often calls this change over time "post-fermentation" or "natural aging" as well.
As for whether this transformation is driven mainly by oxidation, microbes, or enzymes, research and opinion in academia still differ; you can read The Chemistry of Aging Raw Tea. What is certain is that aging raw tea requires a dry, clean environment; moisture pushes it toward mold rather than making it better.
Why Do So Many People Think Pu'er Is Moldy Tea?
- The word "fermentation": Many people hear fermentation and think of mold, but fermentation broadly refers to transformations involving microbes or enzymes; yogurt, bread, and soy sauce are all fermented foods.
- Ripe tea's dark color and pile aroma: New ripe tea's straw-like, damp-earth smell is easily mistaken for mold.
- Impressions of wet-stored aged tea: In the past, some aged teas were stored in humid environments and carried a strong storage taste, giving "old pu'er" a bad reputation. Storage is explained in Dry Storage and Wet Storage.
- White specks on tea cakes: The fine downy hairs on young raw tea and the white frost on citrus peel look like mold but aren't.
How to Check That Your Tea Is Good
- Smell: Ripe tea should smell aged, of jujube, wood, or glutinous rice; new ripe tea may carry a little pile aroma. If there's a pungent, damp, moldy smell, don't drink it.
- Look: The surface should be dry, with no clumps of mycelium or colored spots.
- Brew: The liquor should be clear and bright and taste clean, with no sour, moldy, or stuffy off-flavors.
When you can't tell, the best choice is not to drink it. More methods are in How to Identify Mold.
Keep It Dry in Storage
Tea leaves don't go moldy "on their own"; mold is almost always the result of moisture. Taiwan's climate is humid, so when storing tea, keep it dry, ventilated, out of light, and free of odors, with relative humidity below 70%, and your pu'er can transform as it should. The method is in How to Store Pu'er at Home.
FAQ
Is pu'er made by letting it go moldy? No. Raw tea is sun-dried and then pressed; ripe tea is fermented by specific microbes in a wodui pile with controlled temperature and humidity, which is different from mold growing on damp tea.
Is pile fermentation the same as mold? No. Wodui is controlled, carried out by Aspergillus niger, yeasts, Bacillus, and others in turn; mold is uncontrolled growth caused by damp storage.
Is raw tea fermented? Raw tea doesn't go through wodui when made; it transforms slowly in storage, which the tea world often calls post-fermentation or natural aging.
Why do so many people think pu'er is moldy tea? Associations with the word "fermentation," ripe tea's dark color and pile aroma, impressions of wet-stored aged tea, and downy hairs on tea cakes being mistaken for mold.