Part of the reason, as I said yesterday, is merely caché. Yet there are some other good reasons why many chefs prefer to work with flake salt. For one, it’s easy to pick up. And I mean that literally. Granules of table salt run from between your fingers like tiny ball bearings when you try to pick up a pinch. Flake salt by comparison clumps and allows for easy grasping. It also dissolves quickly, which is nice when you’re trying to correct the seasoning of a food just prior to serving.
Flavor also has something to do with it. Mass-market table salts can have a vaguely “chemical” flavor because of the additives they contain. There’s potassium iodide of course, and to keep that from breaking down, a few stabilizers (either sodium carbonate or a combination of thiosulfate and sugar). Then there are anti-caking agents to keep the individual salt granules from sticking together (silicon dioxide or magnesium carbonate). Then there are the anti-caking agents to keep the anti-caking agents from caking, and no, that’s not a joke. They all add up to less than 3% of the total volume of the salt, but they can affect the taste of commercial salts relative to the unrefined varieties, at least when you sprinkle a little directly on your tongue. Mixed into a dish, well, that’s another matter entirely.
Kosher iodized salt gets quite a bit of use in the Pastry family kitchen, though not for baking. In bakeries, regular granulated salt rules. Sure, a high-end chef might use a little fleur-de-sel to top a dark chocolate tart, but that’s about the extent to which exotic salts are useful for bakers.
UPDATE: Reader Michael F. asks:
I was always told the main reason bakeries use regular granulated salt is because kosher salt has a different density, requiring bakeries to reformulat their recipes if they wanted to use it. Is that true or is it just another Food Networkism?
It’s just their fancified way of saying the crystals are different shapes and sizes, so they don’t measure out the same!