Heartfelt thanks go to Steev Odell, a tea MC-extraordinaire and pu-erh expert, for his vision and the insightful comments he provided. MC Steev has been working with the West China Tea Company to make rare and high-quality varieties of pu-erh known to more people.
Little known to the majority of Western people, pu-erh (also written as pu’er or puer) is a favorite among many tea enthusiasts. Technically, pu-erh is a type of post-fermentation teas, which are produced by allowing tea leaves to ferment before drying. A jewel in the tea crown, it is highly valued by connoisseurs.
Traditionally, making of pu-erh required at least 10 years of fermentation (and the more the better), but since the 1970s means of accelerated fermentation have been developed. These methods of production make pu-erh more affordable for most consumers, who can now drink it with more abandon. Some concerns regarding quality and even safety of modernly produced pu-erh are often unfounded (see more on safety below). The pu-erh produced by modern methods is called “advanced-aged” or “ripe,” while the traditionally aged pu-erh is called “raw.” When the traditionally aged pu-erh is old enough to be drinkable in that dark and earthy sense, it is considered “Mature Raw pu-erh.” However, the terms “raw” and “ripe” are often confused and may be misleading.
To learn some fascinating facts about pu-erh processing and chemistry, just continue reading, or jump straight to Health benefits of pu-erh.
The Fermentation Process
Note: The numbers below link to scientific study abstracts in PubMed.
Fermentation of pu-erh involves multiple microorganisms: bacteria (17880152), including some species that have been found only in pu-erh (18974954, 19406782, 23591759); fungi, such as Aspergillus spp., Penicillium spp. and yeast (18455823, 23957415).
The presence of Aspergillus spp. molds in pu-erh has been the main reason for safety concerns, since these very fungi are known for the production of aflatoxins well-known for their carcinogenicity. However, although Aspergillus spp. were found in a recent study to be the major fungi species present in pu-erh, the researchers did not detect any aflatoxins in 36 pu-erh samples analyzed (23973844)! Another study showed that tea extracts are able to inhibit aflatoxin production by Aspergillus spp.; pu-erh extract, in particular, completely abolished the expression of genes involved in aflatoxin production (23530850). According to a different study yet, the majority of fungi in pu-erh were represented by yeast, not molds (23553377). Furthermore, differences have been found in the bacterial communities between modern, advanced-aged pu-erhs vs. the traditionally aged, “raw” pu-erhs (23957415).
Pu-erh, unlike green tea, has low amounts of catechins (the chemicals normally associated with the health-promoting properties of green tea), since their quantities are reduced by the process of fermentation (12643643, 18968631). A different class of compounds, called theabrownins, is more probably associated with the beneficial qualities of pu-erh. One study describes these compounds as composed of residues of molecules of multiple chemical classes: alkaloids, phenols, nitrogen-containing compounds, hydrocarbons, ketones, furan, alcohol, fatty acids, esters, and amines (23270831). These are unique substances, present in pu-erh in very high amounts (10-14%) (21656777). Due to their complexity and high molecular weight, theabrownins are difficult for scientists to study using normal analytical techniques. Most of the tea catechins, however, are also still present in pu-erh (23187287). In addition, the fermentation process remarkably elevates the levels of gallic acid (18968631, 21793506).
Interestingly, one of the metabolites produced by Streptomyces spp. – geosmin – is known for its earthy odor and flavor, the typical characteristics of pu-erh. Other noteworthy chemicals to be found in pu-erh include lovastatin (used in modern medicine to lower cholesterol levels); however, this should not be a cause for either excitement or concern, as the lovastatin amounts in the tea are quite low: 20-228 nanograms (10-9 g) per gram of dry leaves (23587710), which translates to about 0.07% of a typical pharmaceutical dose per a typical serving of tea. Very low quantities of GABA have been found in pu-erh (17880152); these are also unlikely to contribute to the effect of the tea. Pu-erh produced by modern methods (advanced-aged, or “ripe,” pu-erh) was found to contain more caffeine than traditionally aged, i.e. “raw,” pu-erh (21793506).
Are there any safety concerns with drinking Pu-erh?
In short, no. Although pu-erh is produced by fermentation by multiple microorganisms, including Aspergillus spp., no aflatoxins have been detected in pu-erh (23973844; also see The Fermentation Process). Even at a very high dose, pu-erh was found to be safe in rats (20028013). Similarly, in another study (21134434), the no-observed-adverse-effects level (NOAEL) of pu-erh extracts was found to be 5,000 mg/kg/day in rats, which is equivalent to more than 60 g/day for a normal-weight (76 kg, or approximately 160 lbs) human being. Fluorine levels were found to be low in brick pu-erh tea from Yunnan province, and comparing the numbers against the recommended daily allowance (RDA) makes it safe to drink at 30 g/person/day (9862647). The low levels of fluorine were attributed to the special kind of leaves used in pu-erh.
Health Benefits of Pu-erh
Pu-erh, being quite safe, as shown above, has remarkable effects on the body. The most important of these, perhaps, are its ability to reduce body weight (in overweight subjects) and lower blood lipids and glucose, making it quite a wonderful agent for treating metabolic syndrome. Pu-erh has been used for centuries for its healing properties, corroborated now by modern science. More details on the scientific studies are below.
Pu-erh was shown to reduce body mass index and waist circumference in overweight subjects (21745623), and the effects were visible even three months after discontinuation of pu-erh treatment. The effects of pu-erh on metabolism lead to increased levels of excretion of 5-hydroxytryptophan (serotonin), inositol, and 4-methoxyphenylacetic acid, along with reduced excretion of 3-chlorotyrosine and creatinine (19320437).
Effects on Blood Lipids and Glycemia
Pu-erh decreased fasting and postprandial glucose, serum total cholesterol, triglycerides, low density lipoprotein, apolipoprotein B-100, serum C-reactive protein, tumor necrosis factor-α, and interleukin-6 – the markers of metabolic syndrome – while increasing the levels of interleukin-10 (an anti-inflammatory molecule) and antioxidant blood enzymes (21725873). Similar results on blood lipids and antioxidant blood enzymes were obtained in rats (15656692, 19348878, 19459711) as well as specifically in rats fed a high-fructose diet (22127373). The effects on body weight and blood triglycerides were higher in pu-erh treated rats than in rats given black or green tea (15656692). These effects are associated with the theabrownins, the compounds unique for pu-erh (20722930), and are at least partially related to the suppression of fatty acid synthase (FAS), the key enzyme of fat formation in the body (16925113). In addition, pu-erh extracts showed marked hypoglycemic activity in diabetic mice (23211442).
Potential Anti-Cancer Effects
Various pu-erh extracts used in research studies were able to inhibit the growth of human gastric cancer cells (11302190, 21673927), liver cancer cells (19459711), monoblastic (11302190) and promyelocytic (12643643) leukemia cells, and various mouse cancer cells (22174618), while not affecting normal gastric cells (21673927). Although this is wonderful news, the precise effects of pu-erh on cancer remain unknown until clinical studies are done.
Effects on Oral/Periodontal Bacteria
Pu-erh was shown to prevent the binding of bacteria to human gingival fibroblasts (23578062).
Pu-erh decreased the levels of oxidative molecules in women (16194025), and the oxidative effect of DNA-damaging substances. In other studies, pu-erh was also shown to prevent oxidative damage of DNA (22079314, 12643643) and to protect human cells from hydrogen peroxide toxicity (17032009). In comparing the traditionally made, raw pu-erh with the ripe pu-erh, researchers found that the levels of gallic acid (an antioxidant compound) are higher in raw pu-erh, while levels of catechins (antioxidant molecules found in tea, e.g., green tea) are higher in the modern, advanced-aged pu-erh (21793506). However, other scientists showed that the antioxidant activity of pu-erh is not related to the levels of the typical antioxidant molecules found in green tea such as catechins and gallic acid (17032009). These effects are probably due to theabrownins, the compounds unique to pu-erh (see Pu-erh Chemistry).
Considering all these benefits of pu-erh, outlined above, confirmed by modern science, it may become clear that it is of great help for several major diseases affecting human population today. So, do yourselves a favor, pour some pu-erh! 🙂
(And drink other teas, which have their own health benefits.)