Category Archives: Weather

Humidity

There has been some stuff online in the last few months about Puer storage and humidity/temperature, so I thought it would be interesting to explore the issue a little. See the links at the bottom for reference.

The long dry spell here broke finally with a decent downpour. Prior to that, relative humidity (RH) had got as low as the fourties along with temperatures in the low thirties, which is exceptionally dry for Xishuangbanna.

Aini village long ba men - protective gate. Nan Nuo Shan

Since then, in the last couple of weeks, the temperature has seen highs of 35°C and a low of just above 24°C. The relative humidity has been as high as 84% and as low as 44%. The highs and lows of temperature and humidity don’t of course necessarily coincide in that way; within the broader context of seasonal fluctuations, typically (here at least) humidity tends to drop as daily temperatures rise. Sitting in the shop now, at around mid-day, it is 30°C and 68% humidity.

These short term fluctuations have little impact on the ageing process of Puer tea. More long term, seasonal conditions are what is important.

You only need to tout your temperature/humidity guage around a little to realise a few things:

The first thing that is clear is that making assumptions based on generic weather record figures – assuming they somehow reflect the temperature and humidity inside one’s house, shop, or whatever – is of little value. It gives no more than a broad idea of what might be happening.

In Jinghong, where I can live with all my windows and doors open maybe 360 days of the year, there is a difference in both temperature and humidity between the inside of my apartment and the balcony (outside in the shade), and there is a further difference in a room where I have a little tea stored, to which the door is shut most of the time.

Anyone living in a climate where they are not afforded the luxury of the near ‘al’fresco’ experience that we are here, would be wise not to assume that what happens to the weather outside the house reflects too closely what happens inside.

There is also a significant difference in Jinghong between the ground floor and say the 5th or 6th: Most people in Jinghong will tell you that the ideal storage for tea is between the 2nd and 4th floors. The ground floor may be too damp, the higher floors tend to be dry.

Secondly, as MarshalN has said, it’s of questionable use to consider relative humidity without talking about the thing that it’s relative to. i.e. temperature.

Absolute humidity is the expression in g/m3 of the maximum mass of vapourised water (moisture) that a given mass of air can hold at a given temperature. RH is an expression, in percent (%), of the ratio of actual humidity to the absolute humidity.

Some dim recollection of schoolboy chemistry tells me that the more heat a volume of air contains, the more energy it has, so the faster the molecules are moving around. i.e. they are less likely to condense out and the air can consequently hold more water.

To make a couple of comparisons:

Air with a temperature of 30°C and an RH value of 70% – fairly typical for Jinghong – contains more than two times more moisture (21.36g/m3) than air at 15°C 70% RH – fairly typical of northern Europe – with an actual humidity of 9g/m3. What this means is that with the example given here, a cake of Puer tea in Jinghong would be exposed to twice as much moisture as one in say, the south of England.

Pushing the humidity without increasing temperature is not going to resolve this difference. You need both to achieve a decent Puer ageing environment.

Another example might be to compare Jinghong with say, Nan Nuo Shan, where temperatures are a good 5 to 10 degrees lower, but humidity – there is often mist in the mornings – can be high. So tea that is stored by tea farmers in sacks in their houses can often end up with a musty smell and not infrequently, obvious mould if kept there for extended periods.

nan nuo shan long ba men detail

It seems like dew point is perhaps a more useful measurement of humidty:

Dew point is the temperature to which air would have to drop, for a given absolute humidity, for moisture to condense out – as rain, mist etc.

The dew point in our first example with 30°C and an RH value of 70% would be 24°C and for the second, 9°C. Both are quite feasible, but assume that the amount of moisture in the air would remain constant as the temperature dropped. This is perhaps not likley, but even so, dew point gives a better indication of how ‘wet’ it is than RH does. i.e. how close to the dew point air temperature is.

What this suggests is that on a day in say northern Europe, during which the RH is 70%, if the temperature fell from 15 to 9°C, water would condense out of the air and on to or into something – like your Puer tea.

long ba men - protective village gate nan nuo shan

The fact that that doesn’t happen (hopefully) is because your home is likely not as cold, or humid, as it is outside.

The other thing that is important, is written on every Puer cake wrapper, but few people seem to talk about is airflow. This does not mean a draught. But there is a big difference between 30°C and 80%RH with a little air circulation, and the same temperature and RH with no air circulation.

Half Dipper

MarshalN

Mcintosh Tea

The Road to Gua Feng Zhai

I must have chosen some of the hottest, driest days of the year to take a ride on my newly acquired bike around the Six Famous Tea Mountains. It was Water Spalshing Festival or 泼水节 ‘Po Shui Jie’, Dai New Year Festival – ‘Songkran’ in Thai – which takes place around Xishuangbanna between the 13th to 15th of April.

I spent a night in Mahei before heading up to Gua Feng Zhai.The road runs alongside the San Jia River, crossing over it a couple of times. Sometimes soaring above it, then dropping back down to run alongside again for a while. One is never out of earshot of the river.

A view of the village before dropping down into Gua Feng Zhai. It is currently a little dishevelled as they have been improving the roads in the village and work has not yet been completed. The village is on the Meng Nai River which joins the San Jia He further down the valley. Meng Nai is the Yao name for Gua Feng Zhai.

There are three main tea growing areas with ancient tea trees worked by people fom Gua Feng Zhai; Bai Sha He, Cha Wang Shu and Cha Ping. Due to inherited land use and land allocation, there are many people, other than Gua Feng Zhai villagers who have trees in Cha Wang Shu. There are people in Yiwu who have land in Cha Wang Shu.

The Bai Sha He tea field below is typical of the type of ancient tea tree fields in the Gua Feng Zhai area, but they are all a good 8-10 kilometres from the village. In the immediate vicinty of the village there are only bushes/xiao shu. In this picture the trees are fairly sparse and land around them has been previously cleared. The trees are surrounded by forest. The simple low frame structures in the foreground are used to place bamboo drying trays 簸箕 (boji) on to dry tea.

gua feng zhai tea gardens

Many of the trees have a substantial base, which gives a better idea of their age but, because in the past they were cut back, they mostly have a number of more slender trunks rather than one main trunk. They still grow to significant sizes and can be 4-5 metres tall.

ancient tea tree in Gua Feng Zhai tea field

With all of these tea fields, because they are significant distances from the village, the common practice is to process the tea in the field and then carry the loose maocha out.

Here is a photo looking across from Bai Cha Yuan towards Cha Wang Shu (the mountain to the right). From here it is is a further 2 hour walk to Cha Wang Shu. It is a little more accessible from the other, Gua Feng Zhai, side of the mountain as it can be accessed by motorbike.

Below is a photo of a simple processing facility in Cha Wang Shu. This is where we made tea this spring.

Cha WAng Shu processing facility

Here is one of the bigger trees in Cha Wang Shu. Again, the tree had been previously cut back and then subsequently left untended.

gua-feng-zhai-cha-wang-shu. Ancient tea tree

The scenery around Gua Feng Zhai is among some of the most pristine in the Six Famous Tea Mountains area, not least because of it’s remoteness. Typical tea fields here are at altitudes of 1,600-700 metres.

a view on the road from mahei to gua feng zhai

Making Rain

China’s rain making programme is well documented. Substantial amounts are spent annually on rainmaking technology and its implementation. But Xishuangbanna is mostly still as dry as a bone. A couple of nights ago there was a quite sudden clap of thunder, and it rained briefly, which it seems was ‘man made’, but whatever the potential risks of such endeavors, the effect was quite desultory.

The first flush of tea has finished and pretty much everybody is waiting to see what happens next. By this time last year, despite a dry start to the spring, we had had substantial amounts of rain, but this year, in Jinghong there has been not a drop.

I was up in Hekai for a few days last week, and there it rained a little every night, but Nan Nuo Shan has only seen a little of that. The general consensus is that this year’s tea’s flavour is a little better than last year, but often with a little more astringency. In some teas, the bitterness is more pronounced. We’ll have to wait for another week or so to see what the second flush of tea produces.

 

See here for some more reading on Chinese weather making