Saturday, March 16, 2013

松花皮蛋?! Chinese Century Preserved Eggs

Today we had some relatives over for dinner, they saw from my sister's facebook that we made Hainan chicken rice, apparently they loved this dish and asked if they could come over and try it. My wife and I thought that maybe we should make a few other dishes besides the chicken, so we made a salt and pepper squid and also a tofu with Chinese century eggs. After boiling the century eggs, my wife cracked them open, she asked me to look at the surface of the eggs, she asked me if I could find out what they are, she's pretty sure they're not harmful because they're always on the eggs. They looked like very fine plant roots growing towards the center of the eggs, intrigued I went online to look for some information. Soon I found the following from a website. 
 
"松花蛋又名皮蛋(Preserved egg)。當你敲掉松花蛋外頭的那層泥,剝開蛋殼,就露出了一層青褐色、半透明的蛋白。再仔細瞧瞧,蛋白中還嵌一朵朵漂亮的松葉狀結晶花紋,人們稱之為松花。松花蛋也因而得名。可是,松花蛋上的松花是從哪裡來的呢?
原來,松花蛋上的松花,是經過一場化學反應「雕」成的:蛋白的主要化學成分是一種蛋白質(Protein)。禽蛋放置時間一長,蛋白中的部分蛋白質會分解成氨基酸(Amino Acid)。氨基酸的化學結構很有趣,它有一個鹼性的氨基和一個酸性的羧基,因此,它既能與酸性物質作用,又能與鹼性物質作用。人們在製造松花蛋時,特意在泥巴裡加入一些鹼性的物質,如石灰、碳酸鉀、碳酸鈉等。它們恉穿過蛋殼上的細孔,跑到蛋裡與氨基酸化合,生成氨基酸鹽。這些氨基酸鹽不溶於蛋白,於是就以一定的幾何形狀結晶出來。那漂亮的松花,正是這些氨基酸鹽(Amino salt)的結晶體。
其實,松花蛋的蛋黃呈青黑色,這也是一場化學變化所造成的:蛋黃的主要化學成分是另一種蛋白質,它含有硫。日子久了,蛋黃也會分解變成氨基酸,並且放出很臭的氣體 硫化氫(H2S)。蛋黃本身含有許多礦物質,如鐵、銅、鋅、錳等,硫化氫能夠與這些礦物質生成硫化物。蛋黃變為青黑色,就是因為產生了這些硫化物的緣故。不過,這些硫化物大都極難溶解於水,所以它們並不被人體所吸收。 
另外,因為松花蛋的蛋黃中有很多蛋白質分解變成了氨基酸,所以松花蛋的蛋黃吃起來,要比普通鴨蛋、雞蛋的蛋黃鮮得多。
常聽人說松花蛋不能吃,其實主要是對松花蛋含有重金屬鉛(Lead)的疑慮,但不必太過於驚恐,只要在購買時注意查看松花蛋殼表面是否有黑色大小不一的斑點,若有的話則避免食用。松花蛋營養豐富、味道鮮美,但其鹼性較大,故不宜多吃。有人食用松花蛋時喜歡加點醋,醋能殺菌,又能中和松花蛋的部分鹼性,你不妨也可以試試。" (Taken from http://www.jcctm.edu.hk/~subj_chem/preserved_eggs.htm).
 
Just a bit too much to translate, so if you don't understand try Google translate. This solved the mystery.
 
Check out the awesome fine patterns on the egg.

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