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Empirical Formulas for Storage of Puerh Tea
from Experience to Quantitative Assessment

After fermentation, Puerh tea should be stored in an ideal exterior environment allow the microorganisms in the tea to convert polyphenols and amino acids into aromatic and refreshing compounds. After removal of the unpleasant taste in a well-ventilated place, two decisive environmental factors are temperature and moisture.

Under natural circumstances, it takes as long as decades to transform sun-dried raw tea material into sweet, smooth, and soft aged tea with little bitter or astringent taste. This is a long time to wait for both tea sellers and tea consumers. Thus, people have explored a series of solutions to accelerate the process by turning the raw tea material to ripe tea, or traditionally by storing the raw tea cakes in humid warehouses, as was done in Hong Kong.

According to my experience in Puerh tea storage and post-fermentation, a formula for quantitative storage can be inferred: H•T=CONVP.

Here, H stands for humidity, T for temperature, and CONVP for the constant convertible intensity. When the natural conditions and conversion goal in a place have been determined, the relationship between H and T can be expressed with a simple hyperbola. Like the reciprocal relationship in photography, the formula does not apply to places far away from the indoor temperature and ambient humidity that may cause loss of the reciprocal law.

The formula is intended for two purposes: 1 providing a basis for quantitative assessment of the natural conditions for storage of Puerh tea; 2. quantitative reference far manual adjustment of storage parameters in different environments.

According to Mr. Chen Ganbang, Puerh tea can be classified into three major categories: natural storage, dry storage, and wet storage.

Any location used for storage of Puerh tea should be selected by analyzing and assessing local storage conditions. Proper scientific adjustment should be performed when necessary to reach a solution for optimum storage. Therefore, comparison should be made based on assessment of local natural storage conditions.

Theoretical analysis and actual taste of traditional Hong Kong storage Puerh tea

Before Puerh tea became popular in the 1990s, Hong Kong was the only region to store Puerh tea intentionally and skillfully on a large-scale in a traditional way. Through wet storage, Hong Kong people could remove the bitter and astringent flavor in the large leaf sun-dried tea from Yunnan. In particular, Puerh tea acquired a soft, smooth, and pleasant taste after a long period of storage. The history of Puerh tea storage in Hong Kong provides researchers of the tea variety with key samples and experience in post fermentation with outstanding achievement.

Compared with the handful of stored samples from other regions, in a gradually learned way of storage, the method of Puerh tea storage used in Hong Kong may be less popular today, but local natural storage conditions should be analyzed and assessed. The climate there is warm and summer-like year round, and humid due to the maritime climate, with an annual average temperature of 22.8 C, relative humidity of 78%, and an annual average conversion intensity parameter of 17.78. In July, the temperature averages 28.8 C, the relative humidity 80%, and the conversion intensity parameter 23.04. At the maximum, these three measurements are 37.°C, 95%, and 35.5 respectively.

Based on my years of experience in storing and drinking Puerh in Hong Kong, tea storage by man-induced intervention for 1-2 years appears better than that naturally stored. The raw tea cake s appears darker with some hoarfrost when the surface is observed with a high power magnifier, and it smells of a slight aged (mildew) flavor. In contrast, Puerh tea stored naturally in Hong Kong has no surface hoarfrost, feels like it is solidified or carbonized when put under a high power magnifier, and smells of little flavor. After brewing the tea by yixing teapot, the tea liquor appears dark amber. For the adequately long matured tea, it is obviously carbonized, cotton-like soft, and gaseous. General-ly, tea significantly aged in Hong Kong is of an impressive flavor in the mouth, full of a special Hong Kong mellow taste. In terms used for evaluation of emeralds, it resembles a special pea green base or variety. When you drink such aged tea, you may think that aged Puerh tea must have this mellow taste, and even reject tea aged elsewhere as it may not have the same base or may not be mellow enough.

Storage conditions and tea flavor in Malaysia

The tea sample I tasted was sent from Kuala Lumpur, which reaches a maximum temperature of 36 C and highest relative humidity of 97%, and in May, the highest conversion parameter is 32. The annual average temperature is 27.50 C and the annual average humidity 82%. The monthly average low temperature is 22 C in January, February, July, September, and December, while the monthly average high temperature is 33 C in February, March (58%, for the lowest humidity), April, May (66%, for the highest humidity), and June. The highest average monthly conversion intensity parameter is 21.78 in May.

Natural conditions, customs, and storage of Puerh in Yunnan - theoretical analysis and actual taste

Although Yunnan is the birthplace of Puerh tea, Yunnan people have not traditionally consumed aged tea until the recent surge in popularity of Puerh. With increasing understanding that Puerh grows more fragrant as it ages, many tea drinking friends have come to regret having thrown away so much stored Puerh tea in the past.

For this, there are two major reasons. First, Yunnan abounds in plant varieties with diverse fresh vegetables and fruits in season. Local people are thus accustomed to eating various fresh foods except some preserved foodstuffs used as special flavorings. For example, wild mushrooms are generally sun-dried before being eaten in the north of China, while in Yunnan dried mushrooms can hardly be found in the market. Likewise, when sun-dried tea is found from a forgotten corner and is brewed into an amber soup, it is usually thrown away rather than taken as a drink for continuous consumption.

Another reason is that when local people's favorite drink was sun-dried tea, they tended to select some freshly picked green tea with little bitter or astringent taste, such as tea from Yiwu in Xishuangbanna, where I once invited an old tea farmer with 30 to 40 years of tea drinking experience to taste old Puerh. His surprised expression indicated that the local people had no custom of drinking aged tea.

Because people in Yunnan were not accustomed to drinking aged tea, they naturally did not store Puerh tea on a large scale. However, as Yunnan is the birthplace of Puerh tea, some raw or ripe tea might have been left behind in some forgotten corner, which, after being collected and drank, helped the Puerh tea stored across the province became known to the outside.

Yunnan province features a vertical climatic distribution. The lowest elevation is 76.4 meters at Hekou County in southern Honghe prefecture and the highest is 6740 meters above sea level at Kawagebo summit of Meili Snow Mountain. Within such a range, the outcome of Puerh tea storage, in the low river valleys or the higher hills, basins, or mountaintops, would be completely different. Starting a few years ago, in order to speed up the post fermentation of Puerh tea, tea sellers began to commercially store Puerh tea in Yuan-jiang County, the second lowest place in the province. This tea is characterized by a musty flavor similar to that of Guangdong tea, bright red liquor, little bottom aroma, and aftertaste somewhat inferior to tea stored in Hong Kong. Tea stored at higher elevations, on the other hand, changes more slowly and retains fuller aroma as it ages.

Regarding the natural conditions in the provincial capital of Kunming, it lies at 1880 meters above sea level, at a annual average temperature of 14.6°C, relative humidity of 74%, and an annual average conversion intensity parameter of 10.80. In July, the average temperature is 19.7°C, with a relative humidity of 77%, and a conversion intensity parameter of 14.17. The highest temperature of the year reaches 30.3°C, with the highest relative humidity of 83%, and the conversion intensity parameter of 25.15. When it rains in the summer, the temperature in Kunming drops suddenly to resemble winter. As a result, the conversion intensity parameter tends to be much lower than the highest value.

Puerh tea naturally stored in Kunming is generally characterized by a tight taste in the mouth; tea liquor with all three types of aroma, that is, of the surface, the center and the bottom; thick full tea smell; rich layering of tastes; and differentiable composition. When assessed using terms describing emeralds, the tea resembles a glass base that shows fully its colors and the aromas. However, without adequate storage time, it will turn into the cotton-like quality. When traditionally stored and allowed to develop gradually, the tea ages to become very desirable top grade tea.

The tea production area in Xishuangbanna is 477 - 2429 meters above sea level, at an annual average temperature 21°C, relative humidity of 85%, and annual average conversion intensity parameter of 18.10. In July, local average temperature reaches 30.5°C, at a relative humidity of 77% and a conversion intensity parameter of 14.17. The highest temperature of the year is 38°C and the highest relative humidity is 86% with a conversion intensity parameter of 32.68.

Yuanjiang County, at a lowest elevation of 327 meters, is the second lowest place in Yunnan province next to Hekou County. On the basis of annual averages, the temperature, the relative humidity and the conversion intensity are 23.8°C, 71%, and 16.90 respectively. The highest monthly average temperature (in June) is 28.8°C ,at the highest average relative humidity of 85%, the monthly average conversion intensity is 24.48, and the maximum temperature is 42.5°C.


First of all, the highest conversion intensity is similar in Hong Kong and Kuala Lumpur. But why doesn't tea stored in Kuala Lumpur have the same base storage taste as that stored in Hong Kong? According to our survey and analysis, it is because Hong Kong has a longer climate for maximum conversion intensity than that in Kuala Lumpur. This accounts for the long rainy season contributing substantially to the base storage flavor. Therefore, the maximum conversion intensity has a vital affect on retention of aroma and effective composition.

Secondly, another coincidence is that the monthly average maximum conversion intensity in Kunming turned out to approximate that in Hong Kong, Kuala Lumpur, and Yuanjiang, which indicates that, although the monthly average conversion intensity affects the conversion speed to a great extent, it is not decisive to retain the aroma and composition. Our understanding is that, when the conversion intensity for storage exceeds or is a little lower than that of Kunming, almost optimum aroma and compositions can be preserved and the taste richness can be also maximized.

Thirdly, the simple annually and monthly variance can be analyzed as follows:
Sy= (convph2- convpy2)l/2/ convph
Sm=(convph2- convpm2)l/2/ convph

Here: "convph" stands for maximum conversion intensity, ' convpy" for annual average conversion intensity, and "convpm" for monthly average conversion intensity. The calculation results are the annual average relative variance and monthly average relative variance, to indicate the rise and fall of climatic factors to conversion intensity in a certain scope. The relative variances in Xishuangbanna river valley, Hong Kong, Kuala Lumpur and Kunming increase progressively. Correspondingly, the climate in the Xishuangbanna river valley features tropical rain forest with continuous dampness; Hong Kong, relatively humid and warm insular climate; Kuala Lumpur, peninsula maritime climate; Kunming, plateau climate with sharp temperature difference in the morning and the afternoon and sudden winter-like cold whenever it rains. Consequently, the enhancement of conversion intensity rise and fall in a certain range is helpful for activation of Puerh tea storage, improved taste level, and richness of aroma.

Finally, by means of high-speed photography, we can examine and compare for the first time brewed Puerh tea stored in Hong Kong and Yunnan, as the end of this article.