The people of Zigong have been drilling in the area for Salt since before the Han Dynasty (76-88 A.D.) to extract salt from brine. Some historian estimates are that China has been active in producing salt since about 6000 BC. The brine aquifers in the area have salinity of at least 50 grams per liter. The classical method of drilling and production was the following: a drilling rig is erected and a borehole is drilled using a drilling bit and rope. Brine is extracted by dropping a long tube down the borehole. A membrane valve then captures the brine for retrieval on the surface. Once the brine is retrieved it's then piped to flat pans for boiling. In the boiling process some water and crushed yellow soybean is added. The soybean absorbs the impurities in the salt. Once boiled, a yellow layer is formed - this is scraped off leaving absolutely pure salt. The salt is a medium grain salt with different size flakes which have a very strong and unique salt taste. This salt has no additives so it does clump. Locals use grains of rice in the salt to keep the salt from clumping.