Not very sour sourdough bread

I tried to make some home made sourdough bread in a bread machine and while it turned out okay, it really didn’t have a very sour taste to it.

I created my own started by mixing flour, water, a little vinegar and some regular yeast and letting it sit in a glass bowl covered with a wet towel for 4+ days. I then combined some of the starter with bread flour, water, oil, honey, salt (? I can’t remember if I used salt or not) and bread machine yeast in the bread machine and off it went.

Is there a way to make really sour sourdough bread? Do I need to get a different starter? Let it sit out longer? Use a special starter yeast?

Where do you live? Starters get their “sour” from collecting wild yeast our of the the local air and some air isn’t really all that sour. It’s why great sourdough comes from San Francisco more often than not. They have a richer environment for live culture in their air than we do here in Los Angeles. You can help yourself out by upping the acidity I am told.