Why was the growth of canning in the late 1800s unsustainable?

Canning was unsustainable because the process back then was labor intensive; the process was still undefined, and the materials are very primitive. The cans used were corked and sealed with lead which led it to be hazardous. During the 1860s, a glass jar with a threaded cover called a Mason Jar was used popularly for canning however, these jars were expensive and often are status symbols for the middle class.