16 March, 2012

Humidity and Temperature

I've had some data concerning humidity and temperature lying around for some time, and have yet to write them up; a recent article by His Grace, the Duke of N prompted me to do so - these latter are always a great pleasure to read.

Some months ago, I accumulated weekly mean humidity and temperature data in a comparison of my local climate and that of Guangzhou, on the south end of the Chinese Mainland.  I remember recently drinking some of Keng's delicious Singaporean-style shengpu, followed by a sample of something provided by my friend KC of Hong Kong, which caused me to wonder about the quantitative differences between the climates in my city, and in more traditional Oriental storage locations.


Humidity


It probably should not have surprised me to learn that our damp little island has an amusingly high level of humidity.  Lin Yutang, one of my favourite authors, attributes the "soft skin" of the English to this dampness.  It is interesting to note in the above comparison, however, that our annual cycle appears to be in antiphase to that of Guangzhou: our humidity is at its highest in winter; the Chinese city's humidity peaks in summer (tropical).   Of note is that the minimum Oxford humidity is around the maximum of the Guangzhou data.  

The concern about humidity is that central heating can dry the air.  I have attempted to mitigate this risk by not directly heating our tea-room; the air inside is instead maintained at the humidity of the exterior climate.

However, bringing tea back to England never really worried me in terms of humidity; my primary concern was due to the temperature.




Oxford, and indeed England, is not famous for its high temperatures - we are a dark, northern-European kingdom, after all. The time-series above compares weekly mean temperatures for the same two cities, where we can see that there is a mean-shift of around 20 degrees Fahrenheit between the two.  The mean temperature in Oxford is around 15 degrees Celcius, reaching some 20-to-25 degrees Celcius in the summer (although they have peaking at 34!), and descending to around 5 degrees Celcius in the winter.

The temperatures in my tea-room are maintained at a mean of around 20 degrees Celcius by the intrinsic heat of the structure of the house.  This was, for a long term, my greatest concern, given that the humidity aspect was fine (and actually somewhat excessive).


Tearoom


Ultimately, the true arbitors are the cakes themselves.  Long-term readers of this humble blog may recall various re-tasting exercises (which are enumerated in my Musings page, listed under "English Storage, I, II, ... V").  The evidence from our collection, and from that of teachums (inc. Nada) suggests that England's particular combination of excessive humidity and cooler temperatures results in some fairly decent aging.  However, it is aging of a particularly curious sort.

At one end of the aging spectrum, we have "South China" (the geographical region, which I take to include Singapore, Taiwan, and Malaysia,), which results in the familiar form of "traditional storage", in which we taste classical aging profiles.  Some of my favourite cakes are in this genre.

At the other end of the spectrum, we have Kunming- and Beijing-style storage, where humidity and temperatures are lower, and which result in the "dry" cakes that are becoming more prevalent.

Our English storage is a peculiar midpoint in this spectrum, due to the excess humidity, but low temperatures.  The cakes are not aging rapidly and darkly, as do South-Chinese cakes, and yet they are aging rather well. 

I cannot say how this environment, and the conclusions that we tentatively draw from the evidence acquired to date, can be extrapolated to other places.  I wouldn't like to make any claims about storage elsewhere in Europe, or in the US, for example.


Tearoom


However, I will offer the now quite reasonable body of evidence that the combination of humidity and temperature, as shown in the graphs above, and which represents the conditions of storage in England, has resulted in some very pleasant outcomes in the last seven years.

His Grace, the Duke of N wrote that "temperature is the most important aspect", and it is here that I would like to offer a countervailing opinion.

While temperature is clearly important, the high humidity in England appears to be the deciding factor that keeps our cakes alive.  Although we have lower temperatures here, the cakes are a fascinating combination of "traditional" and "dry" - they are slow to age, and yet they are moist, succulent, and flavoursome.  In a recent round of re-tastes (notes of which are dispersed throughout my various articles), I have found many pleasures in our older cakes, aged here in England.

I speculate that the lower temperatures may merely reduce the duration of the "aging season" each year, which occurs during the summer.  It could therefore be that our English cakes spend longer "asleep" each year than their Oriental counterparts, because our colder season (during which the cakes slumber) is longer.

However, our evidence suggests that Lin Yutang's tongue-in-cheek statement concerning the beneficial effect of the humidity on English skin may also extend to the preservation and development of flavour in our pu'ercha.  It is a development much slower than that of cakes in South China, undoubtedly, but it is a long way from the "dry" profiles of Kunming and Beijing storage.

We'll see in another decade, I suppose, but the interim evidence is encouraging. 

I consider our own experiences to be just one data-point in a much larger picture, as pu'ercha becomes distributed throughout the world.

35 comments:

NorberT said...

a bit off question, but do you know how much tea do you have in your collection?

Hobbes said...

Dear Norbert,

I do indeed - rather precisely! Perhaps unsurprisingly for an engineer, I keep detailed records. :)

(621 cakes/bricks/etc. and counting, monetary value undisclosable but sobering!)


Toodlepip,

Hobbes

MarshalN said...

Interesting observations. Two things to think about, if I may:

1) I think your usage of "traditional" storage here is not what I would call traditional storage. Traditional storage entails enhanced temperature (in excess of 30C) and very high humidity in a closed environment. Such a storage environment encourages the proliferation of mold and other goodies that changes the tea fundamentally. Natural home storage in places like South China are what I would like to call "Natural" storage and do not produce the same taste profile.

2) I think temperature does play an important role in that the absolute amount of water in air changes at different temperature even if relative humidity holds constant. In other words, 70% humidity in the UK and Guangzhou are not the same if one's measured at 10C and the other at 25C. The amount of water in the air at 70% relative humidity at 25C is going to be much higher than that present at 10C. Heating said air to 20C artificially does not, I believe, increase the amount of water present in the air, and will in fact drop the relative humidity even lower because the air's capacity for water increases, and thus encourages evaporation from all possible sources. In such a case, your cakes will actually dry out even faster. I could be wrong, but that's my understanding of how to read relative humidity anyway.

As a result, England's climate pattern of low temperature mixed with high relative humidity may be less beneficial than it first appears, because the amount of water in the air in such a condition is actually not very high. Being indoors and heated (even if the room itself is not directly heated, it's much warmer than outdoors) the amount of water in the air must be fairly low.

All this, of course, is moot if your first series of data is measured in absolute humidity, but I somehow don't believe that's the case here.

Anonymous said...

Dear Mr Hobbes

I would say, without echoing what MarshalN has already explained, that data of outdoor relative humidity isn't that relevant when considering storage of pu erh in any residential houses; in Guangzhou because of air-cons and in Oxford and the rest of northern Europe because of heating and insulation.

The only way to get correct data, if that is your aim, is to buy a hygrometer (five pounds or less at any hardware store).

Although if you are satisfied with the direction in which your tea is moving then perhaps you have nothing to worry about...

Best wishes
Johan

Kate said...

I'm always worried about how bings will do in Canada. I live in Toronto, which is quite humid, but fluctuates between somewhat cold (-10 in the winter) and surprisingly hot (30s in the summer). I have a feeling these swings aren't too great for the tea.

Worse is probably taking tea back to Calgary - it's basically like putting them in a deep, dry freeze. Avg humidity is never over 40% there, and it's very cold for most of the year.

Maybe I should just move to Vancouver and be done with it.

Hobbes said...

I think the most salient part of my article is that which indicates that the combination of noticeably damp air (one can feel it on the breath!) and middling temperatures (peaking in summertime) are resulting in good aging of cakes.

I think good aging of cakes is the take-home message here. ;)


Toodlepip,

Hobbes

Hobbes said...

P.s. My tongue is my humidity measurement device - the air is damp here in the tearoom. :)

Anonymous said...

I live in an old conk shack on an island in the Florida Keys.I have neither air-conditioning or heating.The stone pressed cakes are loosening and fracturing along the edges.Surprisingly the hard pressed bricks seem to be maturing at the same rate as the cakes.In the summers I rotate the tea to avoid white spot mold.In time this climate mellows puerh giving it a subtle aroma.

NorberT said...

My brother lives in England and he said that sometime if you don't use some device to decrease the humidity in the room the "puerh" will grow on the walls, hehe.

Btw, your collection is huge. I think your future generations will be grateful for them :).

Patrick said...

Dear Hobbes,

I'm rather jealous of your massive pu'er collection, although as a college student I suppose I have many years left to collect.

I believe your take home message is a valuable one, and frankly if you are enjoying the way your cakes have aged and taste thus far then all is well. My climate, while similar in temperature, is a bit drier so only time will tell!

I agree with MarshallN, relative humidity will vary on the airs total saturation which does vary by temperature and vapor pressure. However, I believe a more potent effect that temperature will have on your cakes is more a factor of reaction rates. Storage temperatures will often fall within the Q10 range (at least within your household) so microbial, enzymatic, and any other reaction rates will be doubling with each 10C (between 10-38C.) So the difference of reaction rates within cakes during the summer in Guangzhou could be more than twice than the amount in the UK.

But hey we can't all have traditional storage so lets enjoy what we have and savor those occasional gifts of traditionally aged pu'er!

-Pat

Hobbes said...

Dear Pat,

Thanks very much for the data; its interesting that my findings agree: reactions are slower (the tea is aging more slowly than friends' tea in HK or Singapore), but it is aging well - probably due to the dampness in the air.

This was the thinking behind my conclusion that it might not temperature that is the most important factor (up to a point). After all, England does not have tropical temperatures, but we do seem to have a lot of nice tea on our hands. :)


Toodlepip,

Hobbes

Hobbes said...

Dear Nobert,

I haven't heard of a device for decreasing humidity!

I'm currently sat in our tea-room, and can feel the moisture in the air, on the back of my nose. My precious, precious, humidity... :)


Toodlepip,

Hobbes

nada said...

>I haven't heard of a device for decreasing humidity!

They're called dehumidifiers my friend. You'll commonly find them in humming away in damp basements and similar locations.

nada said...

P.s. Thanks for the interesting article. Gives hope for the rest of us storing puerh on our damp, cold little island

Centranthus said...

Very informative post, Mr. Hobbes, thankyou. Here in the old South, the humidity can reach frightening proportions - and it makes me worry how I will be able to store pu-erh should I ever get into that sort of thing. I guess I'd build a cabinet, and leave it go during the summer, and possibly run my humidifier in the winter - which I typically do anyway to promote easier breathing. *shrugs* one will see....

Your collection is stunning. Is it like Pokemon, then? Gotta collect them all....

=) Jess

ZiCheng said...

Hi Hobbes,

This blog post was fun to read, as many of your posts are.

Kate,

My small collection of Pu-erh is stored in my parent's house near Toronto, and in the four years they have sat there, they have definitely aged. My parents disdain to use air-conditioners and heat the house as little as possible, so temperature and humidity swings throughout the year.

Hobbes said...

I hasten to add that my collection (while tiny compared with real "collectors") is a mixed and varied thing, with plenty of dodgy cakes bought when I didn't know better. My advice: take it slowly!


Toodlepip,

Hobbes

MarshalN said...

I think your collection is what's normally called "stamp collection" on Chinese blogs - one (or a few) of everything.

Hobbes said...

Most of my collection is made up of tongs, in fact, so I have 7 of most things. :)

Hobbes said...

A quick check on the spreadsheet: approx. 50% in tong format!

aluoben said...

My pain is that in Poland, Cracow to be specific, we have really dry climate in the winter (and in summer).

MarshalN said...

Hobbes: If my math is correct, then it means you have about 300 stamps? :)

Hobbes said...

Your process of inference would be valid if the assumption on which it based (that one buys only tongs or single cakes) is correct. :)

I need to produce some histograms, I think... There's nowt that can't be solved with graphs. I'll fire up Matlab!


Toodlepip,

Hobbes

MarshalN said...

Stamps can be square shaped!

Hobbes said...

Haha :)

I meant, your conclusion would be valid if one only bought cakes in quantities of 1 or 7! I buy plenty of 3s, 4s, and 5s, if I don't feel brave enough to commit to a tong...


Toodlepip,

Hobbes

MarshalN said...

Ah, I see what you mean. Well, from the vantage point of collectors whose basic purchase unit is jian, even tongs are stamps :)

Hobbes said...

By the time you're buying jian, I think we can stop using the term "collector" and start using the term "investor". :)

You have really got to have confidence in a cake, as a private buyer, to be buying jian, I would imagine.

The thought of fitting even a single jian into my house causes me problems... it'd have to go in the attic or a shed!


Toodlepip,

Hobbes

Hobbes said...

Perhaps I could start using jian as tables...

MarshalN said...

That's what some tea stores do, practically speaking. Two jian of tea, plus a wooden top and you're set.

Incidentally, big factories now only make 6 tong jians, instead of the traditional 12, no doubt to stimulate liquidity in tea trading.

zhi zheng said...

A little after the fact, but I would concur with Marshal N. The relative humidity is inextricably bound to temperature as the temperature of the air (along with atmospheric pressure)determines how much water it can hold and therefor, most critically I think, the dewpoint.

See here for further reading: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html

Hobbes said...

Dear Zhizheng,

Thanks for the additional comment; I don't think anyone is claiming that relative humidity operates in any manner other than that which our textbooks teach us.

Rather, our discussion focusses on the proposition that temperature (in my limited experience) dictates the speed of the reaction (given some sufficient level of humidity), while it is the humidity itself that determines if a cake lives or dies. I refer you to the article, and to our discussion above, for further details.


All the best,

Hobbes

zhi zheng said...

Well, maybe my logic is skewed, but my thought was this:

A typical October day in Oxford might have highs and lows of say 58 and 45°F. If the relative humidity at the higher temperature was 80%, then the dewpoint would be a bit over 51°F, which could mean that (depending on the stability of your 'mean' room temperature) there is the possibility of reaching the dewpoint and moisture condensing out of the air as the temperature drops.

I'm assuming that other factors are constant, which is a big 'if', but my thought is that in a temperate climate this is a bigger potential concern than temperature alone which, as you have noted, will affect the rate of ageing, but should not be damaging.

Of course, if your experience is that the ageing is successful, then it's all academic anyway.

Hobbes said...

They do taste rather good. :)

Thanks again for the comments.


Toodlepip,

Hobbes

Nick Dilks said...

hey, thanks so much for this. This is so useful! heading back to the UK soon, and wondering what to do with my precious pu-erh. I don't think I'll have the luxury of a room exclusively for my tea, so will have to think about this little conundrum some more but your musings on temp and humidity were really helpful. I also like the idea of just letting the tea age in the British way! (rather than worrying if it is as good as other parts of the world). Would love to share some tea with you some day. Maybe I'll bring a cake or two over for you to try :-)

Hobbes said...

Dear Nick,

Keeping it away from the central heating system is the trick, I think, because otherwise the humidity is affected. Perhaps a nice, out-of-the-way storeroom or similar?

Good luck!


Toodlepip,

Hobbes