This is still a mystery to many: some think that everything needs to be baked with steam, others that it only needs a little steam, but it is unclear why, others think that baking can be done without steam.
Anyone who has ever baked rye and wheat bread knows how different their dough is. Wheat dough stretches and springs, rye dough tears and spreads, deforms easily and does not return to its shape.
Why does wheat bread need steam at the beginning of baking? When the bread goes into the oven, it begins to grow actively under the influence of high temperatures: the yeast, before dying from the heat, works actively, the moisture evaporates, the alcohols evaporate, everything in the bread grows and expands. In the oven it grows in the first 15 minutes (on average), increases in volume, its outer layers, which then become the crust.
The steam allows the crust to retain its elasticity and stretch, allowing the bread to grow and the score to open.
Wheat bread can do all of this not just because of the steam, but because it has gluten that begins to stretch while maintaining its integrity.
What about rye bread?
With rye bread, all sorts of turbulent processes begin at the beginning of baking: the yeast starts to rise faster and the bread also starts to grow from the inside, but not as obviously as wheat bread. But: there is NO gluten in rye dough! The dough cannot stretch without losing its integrity, it begins to tear.
If the rye dough is properly moistened at the beginning of baking, the crust will not form so quickly, the surface of the bread will not be able to maintain integrity, it will stretch but crack.
If you sprinkle the crust of the rye bread generously with water and moisture accumulates on the pan, the bread crust will crack in these areas.
Conclusion: You can not steam the rye bread at all or only a little (no longer than 5 minutes) during baking so that the crust is tasty but does not break open unnecessarily.
Have fun baking!