Canning and Pickling Salt
Answer - The salt we buy at the grocery store is usually not pure sodium chloride. Instead it is a mixture of sodium chloride, potassium iodide, dextrose, and an anti-caking agent. In the U.S., salt producers add potassium iodide at a level of 0.006% to 0.01% as a public health measure to reduce the incidence of goiter cause by iodine deficiency. Dextrose, also called glucose, is a simple sugar that stabilizes the iodide. The amount added is less than 0.04% and thus is not a significant source of calories. Calcium silicate is a white, odorless, tasteless, anti-caking compound that has no nutritional characteristics. It is usually added at levels less than 0.5%. It absorbs moisture inside the package that would otherwise cause the salt to stick together and not flow freely in the salt shaker.
Table salt is used for baking, cooking and normal table use. However, it is not recommended for canning recipes because the calcium silicate may cause clouding or settle to the bottom of jar. Furthermore, the iodide may discolor some foods. Niether of these effects make the food harmful to eat. However, the visual quality of the product is adversely affected.
Canning and pickling salts do not contain potassium iodide, dextrose or calcium silicate and thus can be used for cooking, baking, canning, pickling as well as for the table. Because anti-caking agents are not added, it may form lumps in humid weather or if exposed to moisture and should be stored in an air-tight container or re-sealable plastic bag. Kosher salt is usually pure salt and thus is also appropriate for pickling and canning. However, check the label to make sure it does not contain additives.