A 30-year-old bottle of soy sauce found in a netizen’s ancestral residence should be edible, assuming the bottle was properly sealed and stored, and if it still smells OK, said Chang Shih-ming (張仕明), an expert on the condiment.
Chang made those remarks in response to a question posted on Professional Technology Temple, the nation’s largest online academic bulletin board.
The bottle was produced by Tatung Co, the poster said, adding that it was found when the family was having a clear out and it was probably his grandmother’s.
Although the iron lid of the seal was rusty, its smelled delicious and the light sauce had became thick and opaque, the poster said.
Although the government-mandated shelf life of bottled soy is two years, if stored correctly, soy sauce can be kept for decades, said Chang, the owner of Changhua County’s Sinhochun Soy Sauce Factory, a 100-year-old establishment founded during the Japanese colonial era.
“In traditional soy-sauce making, salt is used for preservation and the sauce is sterilized by boiling prior to bottling and hermetically sealed with an iron lid. If kept in a cool area away from direct light, the bottle can keep almost indefinitely without any loss of flavor; in fact I keep a 20-year-old bottle of soy sauce in my shop and it is still delicious,” Chang said.
The simplest way to tell whether a batch of soy sauce is safe to use is by smell, with a rancid smell meaning the sauce has been corrupted by bacteria, he said.
An old bottle of soy should be sterilized by boiling before use, he said.