It must be true, since I read it in a book

I recently got a four DVD plus hard-cover book set titled The Everyday Gourmet: Rediscovering the Lost Art of Cooking from my friendly local public library. It was written by chef Bill Briwa (from the Culinary Institute of America), and published in 2012 by The Great Courses. Lesson 12, Herbs and Spices – Flavor on Demand begins on page 83 with a very curious discussion of salt (my italics added):

“Kosher salt is a very pure salt. Because it is
 ground coarsely, nothing needs to be added to it to make it flow freely or keep it from caking up. Iodized salt, on the other hand, is ground a little bit more finely than kosher salt. Iodine is added to salt to keep it from caking up or to keep it flowing freely. There is also a flavor that is associated with iodine, so iodized salt is not as true a flavor as kosher salt.”

But that is utter nonsense. A quick glance on the side of a Morton Iodized Salt container reveals that the ingredients are:

“Salt, Calcium Silicate (An Anticaking Agent), Dextrose, Potassium Iodide.”

The Salt Institute has a web page on Iodized Salt, and there also is a Wikipedia page on Iodised Salt. Both discuss how iodine instead is added to counter iodine deficiency.

There is another Wikipedia page on Anticaking agent which lists a variety of additives for preventing the formation of lumps in powders. Of course, potassium iodide is not on that list. Recalling high school chemistry and the Periodic Table, you would expect potassium iodide and sodium chloride to behave similarly. And the USDA Agricultural Marketing Service document on Potassium Iodide says it tends to absorb moisture from the air (is hygroscopic):

“Potassium iodide is stable in dry air but slightly hygroscopic in moist air. “     

An image of Abraham Lincoln studying a book was adapted from the Library of Congress.