being finer points or optional additional considerations. Just mapping out scoping related to all the
factors is a substantial project. It’s also relevant to consider what the goal is, why to age pu’er, if the
idea is to enable transition due to aging or just to maintain positive aspects of a tea.
Personal preference for characteristics that tie to different storage conditions is also an important
consideration, related to the subject of enabling fermentation due to aging. It’s at least conceivable that
if someone prefers young (relatively new) sheng pu'er then storing teas in a cooler and relatively drier
environment could be preferable, since these conditions would suppress the transitions related to aging
and fermenting sheng. Most of the following content deals more with setting up conditions that enable
a fermentation process.
To some extent framing is required before starting in on some basics, and at the later point of actual
application of related practices specific goals and expectations come into play.
(photo: aged 2007 version of a "factory tea," a standard mass-produced version)
Airflow / air contact: this gets less attention than humidity but it is still a factor. Some few sources
advocate storing teas sealed inside ziplock bags, or isolated in some other equivalent fashion, but that is
an unconventional preference (covered in a related September 1, 2016 “Tea in the Ancient World” blog
reference). Cakes are typically only stored in a wrapper paper, or that and a relatively air-permeable
outer container, like in the original tong wrappers or in cardboard boxes.
Beyond optimum solution discussions for practical reasons people might want to isolate teas more than
is conventional (eg. if sheng and shu are stored together). In general teas aren’t usually completely
sealed because the bacteria and fungus biomes causing fermentation would need some access to
oxygen, but per experiments on isolated experimental conditions in a second related research-themed
article (on the topic of storage inside mylar envelops) that requirement seems to be limited. In a
humidity controlled environment more zone-oriented sealing or separation at the next level up would
be required, eg. inside a “pumidor” or storage container isolated from outside air contact to maintain a
particular humidity level.
The term “pumidor” is an informal reference to a humidor designed for pu’er storage. It is not specific
related to form of designed enclosure (eg. a repurposed refrigerator versus a designed for purpose
sealed glass cabinet). Cigar storage humidors are often made of aromatic wood components, since
some degree of flavor addition to cigars can be seen as positive, but this approach wouldn’t work for tea
storage, since the idea is to isolate the tea from any external scents.
Temperature: this factor isn’t as commonly addressed as humidity and air contact inputs and won’t be
here. Presumably teas could get too hot or too cold and that would affect micro-organism biome and
fermentation results. A recurring theme in storage discussions is that conditions comfortable for people
are suitable, and that generally applies in this case, that the tea (sheng, for the most part) shouldn’t get
too hot or too cold. A reference on temperature variation conditions cited in a second article on this
theme covers experimentation results in varying temperature. Those results seem to imply that the
upper temperature range isn’t critical, that teas can age well at 40 C (over 100 F), and may age faster
and more positively stored in a hotter environment.
External scents: there isn’t much to add beyond a requirement to isolate teas from external scents
storage in cardboard boxes within a controlled room environment may enable enough separation. Per
some accounts isolation from cardboard is also important (to prevent the teas from tasting like
cardboard), but it is a common and directly contradictory position that cardboard boxes are neutral
enough that they impart no scent or flavor to teas. Storing teas in a basement or a cave could bring up a
different range of background scent issues.
Timing factors related to non-ideal storage: if the idea is to buy sheng and drink it over the next few
months, to what extent does it matter if the tea goes bone-dry? There doesn’t seem to be a clear
answer to this question. Hearsay accounts suggest that sheng can change flavor related to this sort of
exposure, that aspects can fade over a short term, and that re-hydrating a tea can help it brew more
positively, even though infusion in hot water saturates the tea at that step either way. Common sense
suggests that only the fermentation process would cease, but common sense only goes so far in
identifying actual outcomes related to tea storage and preparation. Aromatic compounds in the teas
could be removed under some conditions, in addition to moisture, so temperature may circle back in as
a factor, in addition to humidity being a concern. As with temperature this subject scope will largely be
set aside here.
Avoiding too much humidity / mold: this is a main concern, in the opposite range of avoiding a tea
drying out due to low-humidity storage conditions. Too much humidity can impart a musty smell to
stored teas, and along with inadequate air contact and related to storage temperature mold growth can
potentially occur. Per typical online discussions some types of external mold can safely be removed
from tea (brushed off) and other types cannot safely be removed. It’s best to avoid facing that type of
concern altogether. Tea should never become wet related to storage moisture contact, which can occur
through contact with a less than ideal process to add humidity, or due to changes in temperature
causing condensation. Tea stored in high humidity level might mold (eg. at or above 75% RH), but wet
tea will definitely mold, even at relatively cooler temperatures.
Means to control humidity: the most common storage environment solution discussed in Western tea
circles (in the US and Europe) relates to use of humidity control packs, with Boveda as the most often
mentioned brand. An alternative that might not work for everyone is to simply control humidity in a
personal living space, within a range comfortable to people and favorable to tea storage. Another
solution for controlling humidity in an enclosed space (eg. use of a “pumidor” or other solutions) will be
reviewed at greater length in a second article based on surveying references on this topic.
Ideal sheng storage humidity range to support aging / fermentation
It's important to keep in mind that storage related to long-term aging and simply maintaining a tea to
retain positive condition over a shorter time are different but overlapping subjects.
Most of the discussion here is more oriented towards more ideal long-term storage conditions that
support fermentation (aging) transition in sheng, but this also relates to touching on the other concern,
how to maintain tea over a shorter term in suitable conditions to prevent negative changes to tea
character and aspects.
This isn’t well-defined, but starting a discussion of aging environments requires committing to some
numbers at some point. Or not; it’s possible to never go there, to never specify an ideal in terms of
relative percentage range, but it stays on the safe side of not passing on error at the cost of diluting the
value of content and input. This will embrace the other form of error; committing to more optimum
ranges that not everyone would agree with.
It works to draw on a number of separate sources to help establish and define ideal humidity range:
discussion / hearsay input (personal accounts), expert and research derived input, and the natural
climate in areas regarded as good sources of ideals for wetter or dryer humidity aging environments
(Hong Kong and Malaysia on the wet side, Kunming on the drier range).
Related to the first point, which hearsay? Surveying tea blogs, tea text references, and vendor input
(various forms of expert sources) makes for a substantial project. Input of these types should be taken
with a grain of salt, and to some extent everyone reviewing this subject at the next level of detail should
take up some degree of background reading to cover that same ground. That’s not just to collect up a
personal take on ideal humidity range (only one factor related to pu’er storage environment conditions);
the input passed on along with that detail would serve as useful background related to the other points
mentioned previously, and probably other scope.
One person’s take, this article author’s: roughly a 70 percent relative humidity level environment
represents wet storage (or more humid storage; “wet storage” is used to mean different things). It is
possible to store teas in carefully controlled environments at higher levels of humidity, and this is used
to support rapid aging of teas in some cases, but this raises a risk of negative transitions as well (eg.
mold growth or developing musty character). Attempts to replicate more humid tropical natural storage
would typically not extend beyond use of an 80% RH level environment, with some input suggesting that
this level could be too high to control effectively.
50 to 60 percent is a central range for “dry storage,” conditions under which tea will ferment (naturally
transition with age), but slower than in more moist environments. Given natural variance in humidity
and changes in perspective the 60-70% range may represent an ideal middle ground for storage, or
could be seen as either of the other ranges, especially as drier down towards 60 and wetter nearer to
Around or especially above 70 % RH risk of mold and negative effects from humidity increases, a factor
that varies along with temperature as an input. A tea could taste musty from such contact, depending
on how airflow and temperature issues also factored in. Below 50% RH a pu’er (sheng or shu) would dry
out, natural fermentation (bacteria and fungus activity) would slow down, and at humidity levels
significantly below that such biome activity would all but cease.
(graphic: psychrometric chart showing a rough version of ideal sheng storage "window" in blue)
A reference-source based second article to follow will include other input similar to this specified set of
conditions, but perhaps not identical to it, since that input draws on a number of different reference
sources. Preference for storage conditions could also relate to preference for outcomes in changes in
stored teas, so there wouldn’t necessarily be a uniformly accepted optimum humidity range. Some
references suggest that storing teas in a more humid environment for a reasonably long term (eg. a
number of years) and then returning them to a more moderate humidity level environment for a second
long period of time might be optimum.
Airflow / air contact, temperature, and humidity level act as a group related to concerns. Risk of tea
molding on the wetter side of that storage range is offset by tea having more contact with open air, but
too much air contact could also be problematic. Impact of tea being held on the dryer side may not
correspond as directly to air contact as an input, that is air flow or contact may be less of a concern if
maintaining a high humidity environment isn’t a goal, but this combination of factors isn’t well-defined.
A larger problem seems to relate to how adding humidity could potentially cause wetter conditions in
some parts of the storage, posing a more significant risk.
Adjusting / adding humidity
Discussion of how to lower humidity to bring it a more ideal level rarely ever comes up; few natural
environments are so damp that it would be a factor. Of course there could be exceptions. Air holds
different amounts of humidity at different temperatures so changes in temperature pose a risk for
drastic shifts in relative humidity level, or even worse, for condensation to occur, for liquid moisture to
occur. This is a worst case related to mold risk.
Most typically the question of how to add humidity within a controlled environment comes up. An
obvious but somewhat problematic solution is to maintain a suitable indoor environment throughout a
larger area, to keep humidity level in a home or room within a certain range through use of a humidifier
and monitoring equipment. More commonly storage container or enclosure solutions are discussed,
because these types of solutions enable close control of a limited space, regardless of other shifts in an
indoor or natural environment.
Boveda humidity control packs are often referenced (with background on that product range at
https://bovedainc.com/), and of course there would be other comparable products available and other
solutions that would replicate the same function. One section in a companion second-part article here
covers how to make an equivalent version of these control packs at home.
In a simplest form a sealed plastic storage box using such packs along with a simple form of a meter
would provide a small, low cost-controlled environment. If the goal was medium-term storage (over a
period of months) this environment wouldn’t need to maintain humidity level at any particular level (eg.
at 65% RH) since the point wouldn’t be to support optimum fermentation, only to stop teas from drying
out. Any humidity level at or above 50% RH would support this purpose, that is, any storage conditions
that aren’t too dry.
The ideal setting (humidity target range) and specific configuration for that or other solution alternatives
falls beyond the scope of this simple topic summary. It is debated if using an old refrigerator provides a
good functional equivalent, and some suggest so, with others reject such a context due to plastics used
in refrigerator interiors. Of course foods stored in a typical refrigerator can pick up odd smells, so one
line of reasoning accepts that the same environment may not be ideal related to the same concern and
To move onto the next step of concerns, to consider optimum humidity range, temperature, and air
contact issues in more detail, and to consider specific storage area solutions, requires consulting
external references. A related separate follow-up article takes this step, consulting sources that pass on
specific input based on individual subject expertise, personal experience, or experimentation results.
Article by John Bickel