Since the time of the ancient text, Su Wen (206 BCE–220 CE), and quite possibly longer, Chinese Medical theory has held the belief that substances with Bitter flavors influence the Heart. The tongue’s connection to the Heart was first mentioned in Chapter 5 of the Su Wen, which states that the “Heart governs the tongue” 心主舌 Xīn Zhǔ Shé. In Chapter 23 of the Su Wen it is stated that, “Bitter (flavor) enters the Heart” 苦入心 Kǔ Rù Xīn.
Interestingly enough, modern researchers in Queensland Australia demonstrated that the heart has Bitter taste receptors verifying this ancient theory. Furthermore, they have also demonstrated that Bitter drains fire by showing that the bitter taste slows down the contractile strength of the Heart. This is particularly interesting since Chinese Medicine often uses Bitter medicinals like Huang Lian, Ku Shen, or Da Huang, which are all said to enter the Heart and drain Fire. It’s exciting to see modern research verifying what Chinese Medicine has been saying for thousands of years!
Perhaps more research should be done on the other four flavors mentioned in Chapter 23 of the Su Wen, which states: “Sour enters the Liver 酸入肝 Suān Rù Gān “, “Acridity/Pungency enters the Lungs 辛入肺 Xīn Rù Fèi” , “Salty enters the Kidneys 咸入肾 Xián Rù Shèn” … and Sweet enters the Spleen 甘入脾Gān Rù Pí”.