by Eric Brand

Bob’s recent blog post on the increased extraction efficiency of pressure cooking was a fascinating read for me. The post was commenting on an article written by Mazin Al-Khafagi, which showed significant gains in potency when herbs are extracted in a pressurized extraction machine instead of a stovetop decoction. The article also drew attention to the value in decocting the medicinals together, another rich topic for research and discussion.

Follow up:

This article primarily refers to a specialized extractor that is commonly used in clinics in China and Korea; these machines are essentially automated pressure cookers with temperature and pressure controls, typically coupled with a packaging machine that dispenses the decoction in single dose pouches. Bob commented on the measurable increase in potency achieved by pressure cooking, and remarked that commercial extract producers use similar pressure-cooking technology, albeit with a higher degree of control and sophistication than the “home models” commonly used in individual Chinese and Korean clinics and hospitals. I read this blog post with interest because I have a “home model” Korean extraction machine like the one Mazin uses, and while I have long noticed that the extracts produced by it are quite potent, I’d never had the opportunity to see it presented in a clear and quantified way before.

Specialized Pressure Cookers for Home or Clinic Use

Pressure-based stainless steel extraction machines are a major trend in the field of Chinese medicine. Originally developed in Korea, these extractors quickly spread to mainland China; at present they are the most prominent delivery method for herbal medicine in both China and Korea when convenience is desired. The machines are heavy duty, typically made of stainless steel (though ceramic and glass models also exist); they vary in capacity and are generally capable of cooking 3 to 30 packs of raw herbs per batch. These extraction machines are usable at home or in a small clinic, and hospitals and pharmacies often have a small room with a half dozen or more machines cooking at any given time.

Extraction machines completely dominate the herbal medicine landscape in Korea, and have become integrated into many mainland Chinese pharmacies and hospitals as well. By contrast, granule powders have become the most popular form of convenient, professional-strength herbal medicine in Taiwan and Japan. Interestingly, the varying prominence of these two delivery systems (granules vs. pressure-cooked decoctions) has stimulated the development of herbal medicine in different directions in these areas.

In mainland China, granules have arrived to the domestic market relatively late, and most hospitals only stock granules as single herb extracts. However, the majority of Chinese hospitals, clinics, and large pharmacies have pressure-cooking extraction machines that boil the custom raw herb prescriptions for patients upon request. These machines can be controlled to cook at a specific temperature, and they form a pressurized, contained system that allows for a very efficient extract. The machine generally has a press to remove the potent liquid from the dregs, and the presence of pressure allows the water to reach a higher boiling temperature to facilitate extraction.

Generally, this is an excellent system. Prescriptions can be customized from raw herbs, and the traditional decoction process can be replicated with significantly less labor. Patients receive their decoction in single-dose, durable, heat-resistant plastic pouches that can be easily transported, re-heated, and consumed as needed. A simple method of achieving a vacuum seal allows the pouches to have a decent shelf life without refrigeration, so patients on long-term therapy can prepare several weeks worth of medication at one time. As Bob and Mazin have noted, the pressurized cooking system allows for an extract that surpasses the traditional home decoction in terms of potency and efficiency, and the process reduces the human error of home decoctions in addition to providing convenience.

The efficacy of these home extraction machines has been well-demonstrated, as literally millions of doses have been taken by patients in mainland China and Korea using this method. Personally, I have been very satisfied with my extraction machine, and I know that Mazin also reports good results from his. However, despite their ease of use and efficient extraction capacity, the home extractors do suffer from a few limitations that are not shared by the commercial machines used to make granule extracts (such as Blue Poppy’s products).

Commercial vs. Home Equipment

I strongly agree with Bob’s post regarding the increased potency of pressure-cooked extracts over stovetop decoctions, and I also agree that decocting the medicinals together is very important. In addition, it should also be noted that larger commercial producers (such as the factories that produce concentrated extracts for Blue Poppy) are able to optimize this process far beyond the simple pressurized extractors commonly used in clinics in China and Korea.

For example, home extraction machines pose a challenge with retention of essential oils, whereas commercial operations typically have a more sophisticated method of capturing the oils and reintroducing them into the final product. While a few of the most expensive home extractors do have an added unit to capture essential oils, most of the home extractors do not. Instead, the oils can be captured by allowing the decoction to slowly cool without opening the pressure valve, but allowing the decoction to cool instead of packaging it immediately can potentially affect the shelf life and hygiene of the decoction. Furthermore, the pressure created in the extractor is usually used to effortlessly move the liquid from the extractor to the packaging machine after the decoction is finished. During this transfer to the packaging machine, steam is lost and some of the essential oils may dissipate. For this reason, home extraction machines ideally require one to cook delicate aromatic medicinals separately on the stove, and the short stovetop decoction is added to the packaging machine at the end. This takes extra effort and is often skipped, so home extractors often lose some essential oil in comparison to commercial operations that use a combination of pressure cooking and essential oil capture.

Temperature is another variable that should be optimized and controlled when making extracts. When water is heated under pressure, its boiling point can rise beyond 100 degrees Celsius (212 F). This increase in temperature may offer benefits such as increased solubility of active compounds; however, it does introduce an unknown variable into the equation, as historically the decoctions used were only able to extract whatever constituents came out at the natural boiling temperature of water.

The temperature of the water can be controlled in both small extractors and large-scale commercial pressure cookers. However, in a small extractor, the transfer of the decoction from the pressure cooking machine to the packaging machine is best achieved under a significant amount of pressure. This ideal pressure is typically achieved by bringing the water temperature up to 120 C (248 F) before packaging the decoction. The high temperature and pressure creates a very hygienic and potent extract, but the uniform use of high temperature extraction for all medicinals is common when using small extractors. By contrast, large commercial producers can research the optimal cooking temperature of individual medicinals; the extraction temperature can be better controlled for each individual product, and usually the liquid leaves the sealed pressure cooking container with simple gravity rather than by releasing pressure, so high temperatures and high pressure are not required (the receiving container is usually below the cooking container in a factory, whereas the packaging machine of a home unit is usually above the cooking machine, so it is requires pressure to push the liquid uphill).

Cooking duration is also relatively poorly controlled in a home extractor when compared to the commercial process. For example, when cooking rhubarb (da huang), a short cooking time will produce a potent purgative effect, while a prolonged cooking time will reduce its purgative effect. The short cooking can be achieved by the factory by using an abbreviated cooking time, but the home extractor requires the “add at the end” (hou xia) medicinals to be cooked separately on the stove and added in at the end. The medicinals cooked in a home extractor are all generally cooked for a similar duration of time, because it takes about 30-40 minutes of cooking at peak temperature to build the ideal pressure required to move the liquid into the packaging machine.

Additionally, measurement is somewhat more precise when using commercial extracts instead of small extractors. Small extractors can control the amount of decoction dispensed per pouch, and it is generally quite easy to make the doses per pouch appropriate for each patient. While not lacking in clinical efficacy or ease of use, the home extractors are not able to achieve quite the same mathematical precision that one can achieve when using a precisely measured and openly labeled commercial extract, such as Blue Poppy’s encapsulated products. This degree of precision may not be necessary in clinic, but it is advantageous for easy calculations (or legal cases).

Unfortunately, the litigious nature of American society has hampered the market penetration of home extraction machines here. Most practitioners are unclear exactly how the law classifies an extract for a patient that is cooked in the practitioner’s clinic. Does it fall under a food preparation license? Is it a dietary supplement, a tea? Does it need to be GMP? Clearly there is virtually no enforcement, no massive push by the FDA to crack down on small-scale licensed practitioners cooking up formulas for patients. Yet despite the lack of lawsuits (Marilyn Allen once told me that she’d never heard of a single case of problems with people using extractors), many practitioners remain reticent to cook their own formulas in their office. The labor of cooking the herbs and cleaning the machines, coupled with the gray area of licenses and liability has caused this huge global TCM trend of home extractors to go largely untapped here in the US. Instead, US practitioners tend to favor granule powders or extracts that can be taken off the shelf and given directly to patients in a sealed bottle with full GMP compliance.

Despite these limiting factors of home extractors in comparison with large commercial approaches, they are clearly an excellent delivery system. The home extractors currently dominating the Chinese and Korean TCM landscape are one of the most prominent herbal medicine developments in our time, offering practitioners their own mini-factory, an intermediary choice between stovetop technology and full-scale industrial technology. Their popularity in Asia has apparently reached a critical mass, and I suspect that we will see many comparison studies such as the one Mazin has cited in the future. Seeing the quantifiable improvement in extraction efficiency achieved by cooking medicinals under pressure gives one an appreciation for the sophistication and science of the herbal medicine industry. As pressure cooking is only one aspect of advanced extract production, I suspect that in coming years we will see many more scientific reports that deepen our appreciation for the amazing developments in this modern age of herbal medicine.