There is a common misconception that kosher salt is named so because it must be in accordance with Jewish religious laws regarding food preparation and all the kinds of food that can be eaten. However, that perception is wrong. In reality, kosher salt is not even necessarily kosher but if it's to be employed in a kosher meal it must be. Kosher salt contains only those minerals which are found in the kosher category of minerals and salt. This kind of salt does not contain any other minerals or salts of which the other varieties are kosher salt and kosher moneous salt.
Unlike table salt or regular table salt, which is processed for use as food seasoning in other countries, kosher salt undergoes no processing whatsoever. Its mineral content is completely natural, which is why it's called kosher salt. As such, its use as a food seasoning in the traditional food preparation, for example in food marinades or Eastern European cuisine, is very popular. However, for non-Jewish consumers who want to enjoy kosher salt or kosher sea salt on their kitchen table, they have a few options.
Most commercially prepared kosher salt or sea salt is kosher, but not all kosher salt or sea salt is actually kosher. To be precise, there is a type of salt called "kelpul", which is actually an internal Seafood grading authorities (i.e. one which uses precise laboratory analysis for determining kosher). This grade is actually required by law for salt consumption in the Jewish Dietary Laws. This "kelpul" type of salt, therefore, should be prominently displayed on any table salt grinder that you buy.
"Mined" kosher sea salt, on the other hand, does not have the advantage of being certified by the kosher sea salt grading authorities. In fact, even though kosher sea salt and "heimich" are used interchangeably by people, they are actually two different salts, each with its own distinct set of qualities and attributes. The "heimich" salt has been mined exclusively in Israel and is considered to be of far higher quality than the kosher sea salt mined anywhere else. On the other hand, mined kosher sea salt doesn't contain any real minerals.
One of the biggest drawbacks of kosher salt, according to the kosher salt industry's own definition, is its lack of trace minerals. So how exactly does "heimich" achieve trace minerals? First, most of it's mined in a field in South Africa where limestone is found. The salt minerals are extracted by dissolving the limestone in water and then grinding it up. After it's further processed, it goes through a process called "saltification" where it undergoes a second round of dissolution and grinding before being packaged and shipped to various kosher stores.
Today, most kosher sea salt products do contain trace minerals. One of the biggest limitations however lies in the way it's made and marketed. By definition, sea salt is defined as "any salt that contains one or more minerals". There are no trace minerals in sea salt; it's all just sodium chloride.
This flaw in the koshering process is what led to the "mithurned" symbol commonly seen on kosher sea salts. At the beginning of the 20th century, when kosher manufacturing began to take shape, the "mithurned" symbol was born as a compromise the company would use a symbol that symbolizes a process that leaves behind trace minerals in order to draw in more kosher consumers. At the time, many manufacturers simply didn't want to start using the "mithurned" symbol.
There are some kosher salts that still use the "mithurned" symbol. In addition to the lack of trace minerals, many sea salt shakers lack the quality that makes a product unique. Most have been mass-produced and their texture is sandy and rough like the seawater itself. The result? A product that don't have the unique texture of the seawater, but instead a uniform mass that lack any texture of its own.