Recrisping Bread

The initial bit of mist is to compensate for the drying-out effects of reheating. The finished loaf had exactly the desired ratio of moisture (right?-). If you then put that loaf back in a hot oven, it would lose a little more moisture and become dryer than you intended. Adding a bit of moisture in the form of a mist compensates for this, so the net result is the same moisture content in the loaf coming out of the oven the second time as it had the first time.

(Arguably you might ideally like this "compensation" moisture to start out inside the loaf [of course not all in one spot:-]. That's not straightforward though, so misting the outside of the crust [sometimes more on the botton and sides than on the top] is typical.)

Going a little further, most re-crisping operations are actually doing two things at once: making the crust crispy again, and either un-staling or thawing the bread.

• For un-staling, the conventional wisdom is the bread has become "dried out" and so needs some moisture forced back info it. (This arguably may not really be accurate. But it is the conventional wisdom, it's easy to remember, and it's not known to hurt anything.)

• For thawing if the freezer sack was opened before the loaf was completely thawed, lots of moisture is needed. That's because there were a lot of ice crystals either on the inside of the freezer sack or the outside of the loaf, and opening the freezer sack before the bread was completely thawed lost all that moisture.
  (If the freezer sack were left sealed until the loaf had completely thawed, all that mosture would go back into the loaf. But many folks prefer to thaw loaves in the oven anyway, either because leaving a loaf to completely unthaw at room temperature takes too long, or because too much of the moisture remains in the crust rather than going all the way back into the crumb.)

In either case, most (not all) of the mist recommended for "re-crisping" is actually helping either an un-staling or a thawing operation that's going on at the same time as making the crust crispy again.

My guess (no evidence at all here) as to why "misting" doesn't automatically lead to a "soggy crust" is all the added moisture moves because of the heat. Some of it goes off into the air in the oven; some of it goes into the crumb; but not much of it remains in the crust.

That's the best I can do at a "theoretical" explanation. But a lot of bread-baking is theory-be-damned do what works. If you can construct a reasonable theoretical explanation after the fact, that's nice. If you can use theoretical reasoning as a guide to what to try next, that's even better. But sometimes it's necessary to just "hold your rational nose" and do what works:-)

and time is needed to re-crisp?