Why my rye crumb was gummy
Rye flour has little gluten, so the structure of a rye loaf comes from starch and acidity. That structure is still soft and wet when the loaf comes out of the oven, even if the crust looks finished.
The most common reason for a gummy crumb is cutting too early. Let a rye loaf cool completely, then rest it wrapped for at least twelve hours. Many bakers wait a full day.
Underbaking is the second reason. A tin loaf usually needs a long, steady bake, and the base should sound hollow when tapped. A slightly lower oven for longer is safer than a hot oven for less.