Here is my experience with creating and reducing the sour flavor in bread. I did some googling and learned the temperature that the sourdough ferments makes a big difference in its sour or not sour flavor, and that it is possible to balance out the flavors as you like, but it takes a bit of effort and patience.
In a nut shell, feed it regularly but keep it out in a warmer room if you want it to get more sour. If you have a cooler spot like a cold garage in winter or the refrigerator and feed it regularly, the sourness will go way down after a while.
Here are the details of my experience with the same starter I’ve had for over a year.
I live in a climate that has a very hot summer. Over 100 degrees isn’t rare between July and August. Last summer, I left my starter in my living room instead of the refrigerator and fed it regularly .The starter developted super sour flavor. Last summer’s bread had a sourness was overpowering any other flavor in the bread, even though I gave the dough an overnight rise in the refrigerator to develop flavor in the bread.
The sourness in sourdough starter comes from the same substance that makes vinegar sour, acetic acid. If left out in warm temperature for weeks, my starter developed an unbelievably sour taste and made super duper sour sourdough bread.
Today I make much milder bread with the same starter and it’s delicious. To reduce the overly sour flavor, I dumped out a lot of the overly sour starter fed it more than usual. Initially I fed it more than I normally do. After a while I went back to a usual amount I feed the sourdough. Naturally because the starter spent its time in the refrigerator, the necessary feedings spaced out quite a bit from when I kept it at in a rather hot room.
When I tossed the bulk of the extremely sour starter, regularly fed it, and began keeping the starter in the refrigerator, the over the top sourdough flavor disappeared.