Fire of Metal: Dan Dou Chi 淡豆豉

味酸皆屬金，五味[子]為之主，枳實為木，豉為火，芍藥為土，薯蕷為水。

All sour belongs to metal, for it is governed by Wuweizi; Zhishi is wood, [Dan Dou ]Chi is fire, Shaoyao is earth, and Shuyu [Shanyao] is water.

Dandouchi (淡豆豉) is fermented black soybean (Semen Sojae Preparata). It is not the most commonly prescribed herb in classical herbalism (although it does feature prominently in several of Zhang Zhongjing’s formulas, which we will explore shortly) - to the point that it does not have an entry in the Shen Nong Ben Cao Jing.

One of the earliest mentions of dandouchi in a Chinese materia medica is the Ming Yi Bie Lu (名醫別錄), an herbal text attributed to the Daoist alchemist Tao Hongjing. Recall that Tao is also the purported author of the Fu Xing Jue Wu Zang Yong Yao Fa Yao (輔行訣臟腑用藥法要), the previously lost manuscript that contains the only passages we have of the Tang Ye Jing.

Here is what the Ming Yi Bie Lu has to say about Dandouchi:

豉: 味苦，寒，無毒。主傷寒，頭痛，寒熱，瘴氣，惡毒，煩躁，滿悶，虛勞，喘吸，兩腳疼冷，又殺六畜胎子諸毒。

[Dan Dou] Chi: Its flavor is bitter, [and its qi is] cold and nontoxic. It governs cold damage, headache, [alternating] cold and heat, malarial qi, evil toxins, vexation agitation, stifling fullness, taxation fatigue, panting on inhalation [and] cold pain of both feet; moreover, it kills all various toxins in the six domestic animals, fetuses and children.

Dan Dou Chi, c/o Sea of Chi

We can see from Tao’s understanding that dandouchi is a very versatile herb.

However, there is a seeming discrepancy here: the Tang Ye Jing classes dandouchi as a Metal, and therefore Sour herb, and yet the Ming Yi Bie Lu describes it as being bitter and cold. Modern materia medicas such as Bensky tend to agree with this the Ming Yi Bie Lu's classification, but also emphasize its acrid flavor. 

So how do we make sense of the way the Tang Ye Jing’s classifies dandouchi?

Let’s consider what it means for dandouchi to be considered the Fire of Metal. Going back to our exploration of zhishi as the Wood of Metal, we said that zhishi’s properties can be understood as carrying the action of Metal into the domain of Wood - specifically, through its activity of strongly descending the Gallbladder and breaking knotted qi.

In a similar fashion, then, we must understand Dandouchi’s action as involving the relationship between Metal and Fire. And we know that this involves the Controlling Cycle, as Fire Controls Metal.

Examining Zhang Zhongjing’s formulas with Dandouchi will help make this more concrete. Most of formulas that contain Dandouchi can be found in Line 76 of the Shang Han Lun:

發汗後，水藥不得入口為逆，若更發汗，必吐下不止。發汗吐下後，虛煩不得眠；若劇者，必反覆顛倒，心中懊憹，梔子豉湯主之。若少氣者，梔子甘草豉湯主之。若嘔者 梔子生薑豉湯主之。

After sweating is promoted, if water and medicine are unable to be ingested due to counterflow [but] again sweating is promoted, there will be incessant vomiting and diarrhea. After the promotion of sweating and the use of vomiting or purging, there is empty vexation with inability to sleep; if the condition is severe, with tossing and turning and anguish in the heart, Zhizi Chi Tang governs it. If there is shortage of qi, Zhizi Gancao Chi Tang governs it. If there is nausea, Zhizi Shenjiang Chi Tang governs it.

There’s quite a bit to unpack in this line, and extensive debate in the commentaries over what is meant precisely by many of the terms in this line, such as ’empty vexation’ (xu fan 虛煩). The general consensus though is that xu fan describes a presentation of formless*, stagnant heat in the chest. Improper usage of purgatives, vomiting, or excessive sweating pushes the pathogenic factor further into the body where it becomes trapped in the upper burner. The vexation and anguish described the line are all signs of heat.

Although the line mentions the Heart specifically, in this context the term xin zhong 心中 can be understood as a reference to the chest cavity and not just the Heart organ. Insofar as the chest cavity also houses the Lungs, we can say that this area belongs to Metal as well as Fire. Nausea, vomiting, and shortage of qi (which in this context may simply mean shortage of breath) are also pathologies that all belong to the the Lung (the Metal Organ) and the Stomach (which belongs to Yangming Dry Metal). 

The same pathology described by Line 76 can also arise in Yangming disease; see Lines 221 and 228, which also describe a situation of formless heat in the chest, and for which Zhizi Chi Tang is also indicated. And because Yangming is associated with Dry Metal and its pathology involves heat, we can say that these formulas are working with the effects of Fire and Metal.

To summarize, the clinical situation described by Line 76 is one of heat (Fire) trapped in the chest (which belongs to Metal) – and a key herb to treat this pathology is dandouchi, which opens and vents the Lung, allowing the heat an exit. Dandouchi's cold nature helps to soothe vexation, and this cool temperature resonates with the cool qi of Autumn, which likewise belongs to Metal. Based on this analysis, we can say that the main action of Dandouchi is to protect Metal from being damaged by Fire by venting heat from the chest. It is classified as the Fire of Metal, because it functions to remove Fire from Metal.

Dandouchi features prominently in a number of post-classical formulas where it performs the same function as it does in Zhizi Chi Tang and its modifications. The most famous of these is the formula Yin Qiao San (銀翹散), which is indicated in the Wen Bing Tiao Bian (温病條辨) for Taiyin Wind Warmth (太陰風溫), a pattern that manifests with signs of heat damaging Metal, such as sore throat. It is also frequently added to the pediatric formula Xie Bai San (瀉白散), devised by the Song Dynasty physician Qian Yi to drain stagnant heat from the Lungs.

Although it is beyond the scope of this article series to delve deeply into these post-classical formulas, we can see how their usage of dandouchi follows the same principles as Zhang Zhongjing’s formulas and how in turn one can derive these properties of the herb from the Tang Ye Jing.