Black Tofu & Chinese Chemistry

Do you like black tofu made with black sesame seeds? Quite popular as a healthier (lower carb) form of tofu in recent years, black sesame tofu is made from sesame seeds, starch and dashi is a umami – a rich alternative to white tofu with a delicate, custard-pudding like texture.

black sesame tofu

As usual, there is a cheap “Chinese” version that is available. Well, there is a secret ingredient for every economic miracle. There is a trade secret for turning white tofu black. Not to discourage anyone rom eating black tofu, but do make sure that the black tofu you’re enjoying is not the 黑心豆腐 made in the following way.

I must say that their chemistry is very good. I’m impressed. Iron II sulphate plus sodium sulphide gives sodium sulphate and iron II sulphide (precipitate).

FeSO4 + Na2S = Na2SO4 + FeS

Yes, you’re eating iron II sulphide which is black in colour. Once it enters your stomach, the following happens:

FeS + 2HCl = FeCl2 + H2S

Iron II sulphide reacts with hydrochloric acid in the stomach to give iron chloride and H2S which is hydrogen sulphide (gas). It’s toxic and smells like rotten eggs coming out of your mouth.