Soy sauce was invented by the Chinese over 2,000 years ago and is still a staple of Chinese cooking today.

The traditional brewing method is to place a soybean mixture in large jars and store them in the sun. This method can take up to three years to complete.

An old factory in Rugao, a county-level city in Nantong, is still using this natural fermentation process to produce the sauce.

The technique boasts a history of more than 1,000 years and was listed as an intangible cultural heritage item in 2017.

A worker exposes a soybean mixture in large jars to the sun at a factory in Rugao, a county-level city in Nantong on Nov 9. [Photo/VCG]