Recently I tried a tea recommended by a friend which I found
to be very sour, to the point where I didn’t want to continue drinking it. I’m
not a stranger to sour tea. But of course I feel bad when I think a tea is sour
because I know the reasons why. The question is whether the tea is a loss or
still has hope of further transformation. I’d like to recommend reading as much
as you can about fermentation in general, along with puerh fermentation
articles when you come across them. Using a very informative book published
last year, Modernization of Traditional Food Processes and Products, (A.
McElhatton and M. El Idrissi, eds. Springer, 2016), I will attempt to apply the fermentation concepts described in this book, and explain sourness in a more approachable manner in the
context of puerh storage. Hopefully then I can pick out a cause for what I
taste in my friend’s tea.
Sour flavors in puerh tea are due to acids which are
secretions, or by-products, of bacteria and enzymes. In any fermentation
process of vegetable matter, acid formations are normal and an important stage
toward getting the finished product you want. A mild sourness is indicative of
a desirable stage in slow-aging sheng puerh. Acid formations provide a
favorable environment for growth of fungi like Aspergillus niger and Penicillum,
but also provide an unfavorable environment for putrefactive bacteria so that
the product does not spoil or rot.
Fermentation, to put it simply, is a three-stage process of
bacteria->to acid-> to yeast in which all three are in enough of a
balance that the correct bacteria and yeast will grow at each stage. Gallic
acid, among others, is the primary compound responsible for a mild sour flavor
when puerh is aging well. Aspergillus fungi such as niger, foetidus and
Penicillum also produce a mild gluconic acid as the result of fermenting
glucose sugars. In the middle of fermentation, a mild sourness is normal.
However, other acid products are produced during
fermentation as well. When acids get overly abundant, beneficial bacteria and
fungi cannot continue to develop and the next stage of fermentation cannot
progress. Either the tea doesn’t make it to the stages responsible for breaking
down bitterness and developing flavor, or the tea ferments too fast and breaks
down before the good yeasts get a chance to add flavor. So, we can end up with
tea that has too many acids and didn’t properly progress to the next microbial
stage. Let’s take a look at some of the possibilities for overabundance of
acids.
Too High Heat and Humidity
Several organisms can grow out of balance when tea is stored
or fermented in too hot conditions. The enzyme Rhyzopus is active at temps of
32-40C and is important in breaking down the starchy cell walls and pectin in
the tea. This will allow for an effective release of tea juices into an
infusion, and add fragrance. So this enzyme Rhyzopus is important in
fermentation of puerh tea. Rhyzopus secretes fumaric acid, lactic acid and
succinic acid. While breaking down the cell walls of the tea leaf is the
desired function, an overabundance of Rhyzopus will break open the structure of
the tea completely. In a high-heat situation with too much Rhyzopus, your tea
cake will develop mushy, melded spots because the leaves are breaking down into
wet globs.
Too-wet tea that arrived moldy. The globbing of the leaves is evident near the neifei |
Too Cold and Dry
Lactic acid is an important part of fermentation because it
creates positive conditions for beneficial yeasts like Aspergillus niger.
Aspergillus niger is a carbon source of food for Saccharomyces yeasts which are
responsible for transforming the bitterness in tea into sweet and mellow
flavors. As long as the acid environment is under control, in late-stage
fermentation the Saccaronmyces yeasts will get their opportunity to convert the
bitterness in the tea into nuanced flavors. This is because Rhyzopus has done
its job to break open the cell walls and make the plants juices available to
this yeast. But when a tea is too cold and dry at the start, Rhyzopus may not
sufficiently grow to break down the cells of the tea. Fermentation cannot
progress and the tea appears green and young.
Both Rhyzopus and Saccharomyces need sufficient heat and
humidity to grow. A too-dry and too-cool environment means the tea is stuck in
a state where the earlier yeasts and bacteria produced the correct acids, but
fermentation stopped there. If kept in this state for too long Aspergillus and
Rhyzopus will die out, and their waste carbon products needed for Sacchronmyces
food are no longer available. Thus the Sacchromyces yeasts will never get their
chance to develop those lovely flavors from the bitter plant juices. In
addition, our friends Sacchromyces are responsible for clarifying the juices
from cloudy to clear. The tea will remain bitter and acid sour, and the brew
will be cloudy. Fragrance too is gone.
This is what produces the familiar “dry storage sour,” but
unlike the too-high heat situation, if the tea is not cold and dry for too long, then heat and humidity can be applied to correct the stuck tea and get fermentation
moving again. When puerh collectors complain about “too dry and cold”
conditions in the west, they are referring to the possibility that western
collectors cannot provide enough heat and humidity. Thus their tea will remain
sour and dry until it passes a point of no return when all the microbes are
killed off. The tea tastes flat in addition to dry and sour.
Charred Leaves in Chaqing
Another cause of dry storage sour is char produced by the
wok in processing the maocha. Burnt smoky tea is an addition to the puerh cake
that is not intrinsic to it. The tea is altered by the addition of burnt
carbon. Heat and humidity can speed up the usage of this carbon by yeasts, but
the fragrance and flavor produced by the char may overpower the subtle flavors
produced by Saccahromyces. In my experience, char is the most common cause of bad
flavor in puerh tea because it’s an addition to the tea that will not go away
by the normal slow fermentation process. It requires a correction of high heat
and humidity for the perfect amount of time, and the perfect time is rarely achieved.
Puerh collectors are accustomed to accepting this
processing flaw as “ordinary” when in fact it is not. “Retired smoke” is not caused by improper fermentation, but a condition imposed on the tea leaf during the
wok process of chaqing used to stop the oxidation of the tea leaves prior to pressing. Another cause for smokiness is when chaqing is performed in a closed, smoky room such that the
odors from wood burning permeate the leaves. I feel sad when I taste this, because a fine leaf may
never get a chance to be what it is meant to be. Poor leaf, well, nothing lost
and nothing gained. Yet many collectors are so accustomed to char or smoky flavors that it is
accepted as a normal condition. Indeed, many people have learned to like it. Once in awhile I like it too, even though I think it is a flaw.
My favorite Manzhuan tea developed some flavor from char. Breaking up the cake into a clay jar for a few months corrected the problem, and I no longer taste it. |
Glad to know my parameters coincide with what you know. Gives me hope for the future.
ReplyDeleteThank you. you are awesome. This information is very well presented. Cheers from a long time reader.
ReplyDeleteVery useful information, thank you.
ReplyDeleteJenn K.
how long do you think is the point of no return for cold-dry? a month? 6 months? I'm at 20% humidity right now and my humidifier is on the way
ReplyDeleteDepends on the condition of the tea to start, but otherwise the tea just will lose aroma first and go dormant, would take a couple of years to kill it
Delete