sourdough bread vs sour bread

sourdough bread and sour bread both are nouns.

Word	Noun	Adjective	Verb	Adverb
sourdough bread	Yes	No	No	No
sour bread	Yes	No	No	No

As nouns, sourdough bread and sour bread are synonyms defined as:

sourdough bread and sour bread: made with a starter of a small amount of dough in which fermentation is active

sourdough bread (noun)	sour bread (noun)
made with a starter of a small amount of dough in which fermentation is active	made with a starter of a small amount of dough in which fermentation is active