Really sour smelling commercial loaf sandwich bread

My brother in law has a small sandwich shop and he's asked me to try and replicate the commercial "sourdough" pan sandwich bread that he uses for one of his sandwiches. Now, I can't say for sure it is actually traditional sourdough because I haven't seen the ingredient list. The bread is a pretty standard looking white loaf bread although pretty large. One of the characteristics of this bread that I'm having trouble finding solutions for is a pretty intense sour smell. I bake mostly artisan style sourdough and although it doesn't smell particularly sour it has a really nice sour tang. I have searched and searched the internet for hints on how to reproduce this "smell" but can't find anything concrete. I know you folks know just about everything there is to know about bread so I'm hoping I can get some input here. Thanks so much.