Michigan State University Extension
Preserving Food Safely - 01600734
Some old pickle recipes call for a bluestone to be added to the pickling brine to give the pickles a blue-green color. Bluestone is copper sulfate and is also known as blue vitro. In earlier days, pickles were usually made in metal pans containing copper. They turned a bright blue- green as the copper ions interacted with the chlorophyll molecules in the pickle. A similar color was sought for pickles brined in enameled pan or crocks, and it wasn't long before copper sulfate, or bluestone, was found to do the job. Since high levels of copper can produce toxicity symptoms in humans, particularly gastrointestinal problems, the use of copper sulfate in pickling should be avoided. Since its only function is to color the pickles, the bluestone can be simply eliminated from the recipe without affecting the overall quality of the final product.