Sunday, January 23, 2011

Pharmacy Term of the Day: 后下 Hou Xia

When you write a Chinese herbal formula and send it to Fat Turtle, it's a little bit like telling the cook exactly how you want your eggs. Over easy? Over hard? Scrambled? Sunny side up? Maybe you want something fancy like benedict?

This is the first in an occasional series highlighting the special instructions you as a Chinese medicine doctor can give to us, the herbal pharmacy, to make sure your patient cooks the formula correctly.

Today we'll be looking at the term "Hou Xia" (hòu xià 后下). "Hou" means behind or at the end. "Xia" means down, lower, underneath. A crude translation would be "throw down at the end", giving you the picture of herbs saved off to the side and then "thrown down" into the pot when the cooking is nearly done.

Some typical herbs that are packaged separately and labeled Hou Xia are:
  • Mu Xiang 木香 Aucklandia Radix
  • Sha Ren 砂仁 Amomi Fructus
  • Cao Dou Kou 草豆蔻 Alpiniae Katsumadai Semen
  • Da Huang 大黄 Rhei Rhizoma et Radix (when used as a purgative - when used as a blood mover Da Huang should be cooked together with all other herbs)

The rationale for preparing herbs in this way is that there are volatile oils in these herbs that cook off very quickly. Cooking for 5-7 minutes can release these active ingredients into the formula, while cooking longer than that boils them off into vapor.

The vacuum packing service that Fat Turtle offers necessarily cooks all the herbs together at once, even Mu Xiang and Sha Ren. Does this reduce the efficacy of these herbs? Surprisingly, the answer is no. In fact, the effectiveness may even be increased.

An article published in the Zhejiang Journal of Traditional Chinese Medicine (浙江中医杂志 Zhe Jiang Zhong Yi Za Zhi, Vol‐9. 2005; Weiqing Liang, Junxian Zheng, Jinbao Pu, Kemin Wei) found that extraction of flavonoids and alkaloids from herbs decocted in vacuum cookers is higher than traditional stove top cooking. The extraction of alkaloids from Mu Xiang from traditional cooking was 0.045%, while with vacuum cooking the extraction rate was 0.094% - more than double.

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