Monday, July 31, 2006

Geraldo on oxidation in aging pu'er

[[from an email to corax. posted by permission.]]

I've read dogma_i's post on "Container materials for tea storage" several times now, and I admire the rather full treatment of the subject in one wrapper, so to speak. Besides having much to impart, it also rekindles an idea I've had floating in my head for a little over a year now.

First, some background: I live in the center of the nation's biggest tree fruit ag region. Growers try to stretch their harvest period by planting at various altitudes, but still the harvest period for each fruit (cherries, apricots, plums, peaches, nectarines, and apples) is rather short, and that is not good for fruit prices. Therefore, quite a bit of research has been carried out in controlled atmosphere (CA) storage. In my little town are mammoth CA warehouses. Big corporations and cooperatives store fruit -- especially apples -- in giant vaults from which normal air has been flushed, and in its place they've pumped in what I'm guessing is nitrogen and other gasses. At the same time they lower the temperature to just above freezing. This has the effect of prolonging the fruit's shelf-life. What they do not want in their CA warehouses is oxygen: it makes the fruit age.

More background: About twenty-one percent of our atmosphere is comprised of oxygen. What is accelerated decay to warehoused produce may be life itself to the ailing human body: Hyperbaric oxygen therapy places patients in an environment of pure oxygen under several times the normal atmospheric pressure, pressure much like conditions encountered by divers and by deep-sea explorers in bathyspheres and bathyscaphes. Indeed, some hospitals employ these very undersea vessels in their therapy units. Although the vessels are securely bolted to the floor and not lowered under water, therapists actually refer to the hyperbaric oxygen sessions as "dives."

More background still: Besides those victims of the "bends" who make use of a hyperbaric environment for alleviation of their painful condition, patients suffering from a variety of health problems -- including diabetes, carbon-dioxide poisoning, and radiation damage -- find that hyperbaric oxygen therapy is often conducive to healing damaged tissue that might otherwise not heal, by allowing oxygenated blood to travel to damaged areas. The increased atmospheric pressure of the hyperbaric chamber, as I understand the process, breaks the oxygen into smaller particles, allowing the richer blood to travel to -- and help to regenerate -- damaged capillaries. Eight summers ago I myself underwent extensive hyperbaric oxygen treatment at Seattle's Virginia Mason medical center. The equipment at Virginia Mason is quite complex, much of it operated by Navy SEALs and doctors outside of the bathysphere and medical staff within the bathysphere. Each day I spent about two hours in a pressurized chamber, breathing pure, pressurized oxygen, in an attempt to stimulate the regeneration of capillaries in my jaw. The treatment, I'm happy to report, was a success.

Now to tea: To my knowledge, the aging of pu'er entails several factors, including temperature, humidity, fermentation, enzyme activity, and oxidation. I haven't a clue as to which of these plays the biggest role. But I do know this: If I were a pu'er-collecting medical doctor working in the Virginia Mason Hyperbaric Department, I would absolutely run an experiment to explore the effect of hyperbaric oxygen on changes in pu'er. I'd use four beeng chas -- same production, same vintage. I'd flake up two of them. I'd keep one compressed beeng cha and one flaked beeng cha in the hyperbaric oxygen chamber and the other flaked and compressed beeng chas in a "normal" aging environment. At the end of some pre-determined treatment period (a month?), I'd compare the hyperbaric beeng chas with the non-hyperbaric beeng chas. (Sadly, I cannot undertake that experiment.)

Regarding the finer points of science and technology, I don't know very much at all. However, some readers of CHA DAO may. It occurs to me that one need not have at his or her command a big, hospital-style bathysphere with crews of medical and technical specialists to monitor it. A hyperbaric chamber need not have room to seat five patients and three PA's. A tank no bigger than a stovetop pressure cooker would suffice. I know that hyperbaric oxygen delivered for short periods over a span of weeks is more salubrious for most medical purposes (excepting bends) than one long, hyperbaric oxygen session.

The procedure for subjecting pu'er to hyperbaric oxygen might be somewhat complex. As an ex-homebrewer of the most ardent sort, I initially considered the simple step of placing some pu'er in a small soda canister or beer keg and pressurizing it with oxygen obtained at a welding-supply store. But then I recalled that my own time as a hyperbaric oxygen patient was not that straightforward. In each hyperbaric session, the chamber was pressurized to the equivalent of eighty feet below sea-level, and then we breathed pure and pressurized oxygen supplied in a steady flow via oxygen hoods that we wore over our heads. I suppose, therefore, that oxygen flow is an important part of hyperbaric oxygen treatment, and I cannot conceive of a method whereby a home-based researcher could recreate those conditions on a small scale without a very big investment in time, energy, and money. A device whereby oxygen can be held pressurized in a tank is rather easy to visualize, but a pressurized device with flowing oxygen inside it is somewhat more challenging to one, like me, with few technical and scientific skills. I'm certain, however, that somebody with more expertise and creativity can invent an elegant and parsimonious apparatus and procedure.

I'm not asserting categorically that hyperbaric oxygen will radically speed up the aging of pu'er, but wouldn't it be really, really cool if it did?


Keith said...

Hey Gerry--

I read your post with interest. While not in my specialty, I know more about hyperbaric therapy than I do about pu'er aging. And I thought you might be interested in a medical perspective.

Before discussing the hyperbaric therapy, I should note that it is a controversial treatment, and has detractors in the medical community.

Hyperbaric treatment is theoretically useful in increasing oxygen delivery in hypoxic tissues. Take the classic example of the diabetic foot ulcer. Diabetics are prone to developing small artery atherosclerosis, causing impaired blood flow to their feet and other organs. Because of this (and because of diabetic neuropathy) they are prone to developing nonhealing ulcers. As infection from the nonhealing wound spreads, amputation is often necessary.

The ulcers can't heal because they are hypoperfused and thus hypoxic. The best treatment is improve blood flow. This can sometimes be done with medical, perucutaneous, and surgical treatments. However, in advanced cases restoring blood flow is often not possible.

Enter the concept of hyperbaric therapy. If you can't improve blood flow, perhaps you can increase blood oxygen concentration, and deliver a reasonable amount of oxygen even with decreased flow. Note that this solution does not improve delivery of other nutrients nor improve removal of toxic metabolic products.

It turns out the hemoglobin is well saturated with oxygen under normal conditions. If you breathe 100% oxygen you load up your hemoglobin with only slightly more oxygen. However, a small amount of oxygen directly dissolves in the blood. This is a minute amount under normal conditions. But if you increase the atmospheric pressure dramatically, a significant amount of oxygen gets dissolved in the blood. This is the theory of hyperbaric therapy: high pressure oxygen to supersaturate the blood, to provide hypoperfused tissues with oxygen.

While necessary for life, oxygen is not benign. Oxygen metabolism is the primary free radical generator that damages DNA and other tissues. It is thought to be a primary cause of the aging process. In fact, breathing high concentrations of oxygen is toxic and cannot be done safely for extended periods of time.

Like humans, pu'er also ages through oxidation. But unlike an ischemic wound it does not depend on a trickle of blood for its oxygen. Increasing pressure may increase the rate of pu'er oxidation. But I suspect that other factors, such as temperature, light, and biological activity may play much more important roles. Oxygen must be present for oxidation. But I don't think greater oxygen concentration would be an efficient way to speed oxidation. Any biochemists reading this please feel free to correct me :)


Geraldo said...

Keith--If you happen to see this, thank you sincerely for the insights and opinions. How cool to receive a free medical opinion! :-) Seriously, your expertise is much appreciated (and admired). All the best, Gerry

~ Phyll said...

While I lean in agreement with KPM's comment: "...I suspect that other factors, such as temperature, light, and biological activity may play much more important roles," yours is an interesting hypothesis! In wine, O2 also plays an important role in the aging process. I've read many articles on wine experiments, and they all seem to point that rapid aging through increased oxigenation rate does not bode as well for the wine as slow aging in the cellar. In long term cellaring, O2 seeps ever so slowly through the pores of the cork stopper. In addition, temperature and lack of vibration as well as light are also important factors.

I can't say I know much about what actually takes place during pu-erh aging process. But wine and tea, esp. pu-erh, are both agricultural products that can share similar traits.

Please correct me if I'm wrong.



Sean said...

Get article Gerry, and a very interesting proposal! Reading it acually brought a few questions to mind.

Has anybody out there conducted a study on what ages pu-erh and how it occurs? I know that many people cite slow microbial and oxidative processes, but has this actually be empirically shown to be the factors at hand? Has the progressive steps of aging and causes of it been documented? Is this backed with good data? IMHO, the lack of this knowledge sadly leaves us with only 2 ways of getting the rich, pungent, and silky experience that well aged pu-erh provides: (a) blindly guessing at cruddy aging methods, or (b) having to wait several decades.

In many ways, people have been trying to develop effective accelerated aging methods (AAM) for pu-erh for many years. Just look at cooked pu-erh and "wet-storage", or even the flaking-pu-erh-bing-into-a-jar method. However, these technique are only half-attempts at a good AAM , and often give dissapointing, mediocre, or in somes cases, even dangerous results (for example, mold toxins).

I just think that a scientific study is probably the best start to begin formulation of an AAM that gives good results. If this were done, perhaps then we can begin to accurately emulate and "properly" accelerate the conditions for pu-erh aging. Thus bringing great inexpensive aged pu-erh to all man-kind.

That's enough of my mindless blabbering. Again, thanks for the post.