Non sour natural yeast?

I've found that my sourdough starter can be kept well out of range of being sour by simply keeping it well fed with unbleached white Bread or All Purpose flour. For even more blandness, try using bleached AP. I feed it such that it just reaches peak before I feed it again. In my case, that is a feeding ratio of 1:2:2 of starter:water:flour every 12 hours if left at room temp, or once a week in the fridge. When making bread, I only let the dough rise until doubled, shape, final proof (not overproof, as you found out) and bake. If you wish to use whole grain flour to feed the starter, there is some risk of it turning a little sour even if well fed, and very sour if left a little neglected. Also, the timing will be quicker and less predictable, especially in a warm room. You can make whole grain bread with a white flour starter, though, usually with no problem.

The natural yeast that seems to be the most comparable to commercial yeast in my experience is Yeast Water. It is started most easily by putting a few raisins in some non-chlorinated water, sometimes with a little added honey to get things started. Once it begins to bubble a little, it is fed daily with a few more raisins and a little bit of sugar. Very clear, detailed, and well written instructions can be found on this site by searching for 'yeast water' in the search box at the top right, so that is all the detail I'll give here. It is easy to maintain, and can also be refrigerated. It won't impart very much flavor usually, considering the small amount used in making bread.

To use it, you simply replace some (or all, if you have enough) of the water and all of the yeast in your recipe with Yeast Water. If your yeast water is well fed, there will be excess sugar in the water which needs to be accounted for in the bread recipe. If you're accustomed to using a little bit of sugar or honey in your bread to help boost the rising power of the yeast or to make your bread softer, you can reduce or eliminate that amount of added sugar. Or, you can go ahead and add it in and your bread will be sweeter to the taste after baking. Yeast Water is better at raising dough than a sourdough starter, or at least it accomplishes the task a little bit more quickly. I think it is because the flour in the starter is practically used up, yet it counts as flour in the recipe, while Yeast Water has no spent flour in it, so all the flour in your recipe is fresh food for the yeast. I could be wrong, but it seems plausible anyway.

It's not the yeast that makes it sour, but the lactic acid bacteria in your culture. There's always going to be a higher concentration of those bacteria in a natural levain bread than one risen with commercial yeast, but you can minimize the sour. Bacteria take longer than yeasts to do their thing, so you can get good leavening without too much sour buildup by using the levain when it's "young", which is to say a little before when it might normally be considered mature, when there is good yeast activity but the bacteria haven't caught up. If you look at recipes from Chad Robertson for his Tartine bread, this is the technique he uses. Another thing is how you care for your starter. If you do infrequent feedings and keep it in the refrigerator, it will probably be more sour. Doing 2 or (even 3 depending on your room temp) feedings a day each time it reaches maturity will keep the yeast populations high and the bacteria down.

It seems to me that anytime I find a wild yeast that feeds on added fructose or adding table sugar (half fructose) honey (more than half fructose) or fruit (lots of fructose) lots of little genetic switches get turned on/off and you come out with a non-sour sourdough.  You can still let mother starters peak and mature to maintain their health, but their inoculated children (well fed babies starters for our loaves) tend not to be sour.

Take that for what it's worth.  In other words, also feed your starting starter with something sweet.

There's a few techniques for keeping the sour out of your bread, one of the ways is a "young" levian as mentioned by an earlier poster.

i've found that a series of sucessive "short feeds" works really well, such as feeding your starter every 4-5 hours a few times before your final dough gets mixed.  Yeast reproduce quicker than the bacteria do (the ones that produce the more "sour" tastes at least), so by feeding the starter after such a short time, many times in a row, favors yeast production over bacteria production.

Another way to keep a starter "sweet" is to do an italian sweet starter, like the one that is used for panettone.  this starter is generally kept very stiff (between 40-50% hydration), warm (up to 90F), and bound (wrapped up tightly with plastic, then tied with rope).  This starter is also fed every 4 hours.  Lots of work, but after 4 feedings or so will actually start to smell sweet, it's fastinating.

yeast water,  it is cultivated yeast from nature and maintained  using fruit and water as opposed ti flour and water.  Since there is no LAB in the mix it is never sour yet can make bread rise explosively on occasion,  Type YW Pimer in the search box and follow the directions to make and keep YW.  Much easier thanSD by the way  I use mine any time sour isn't wanted or needed. You won't need commercial yeast ever again - and sour socks ever showup in the bread.

Happy YW Bread Baking! 

Actually any sourdough starter can build the base.

As Mini Oven mentioned, you should just use it as mother starter and built your leaven/levain from it. This leaven will be young (see ericreed's post). There is a technique developed in Germany after WWII when bakers yeast was not available or still expensive, and later optimized by another institution, called "Schaumsauer". The literal translation would be "foam sour". The trick is, to develop a leaven over multiple steps with high hydration (fist step 200% - twice as much water as flour, very liquid) and in each step mix it well with a whisk to bring in air.

A wetter environment pushes the yeasts in the sourdough and also the oxygen whisked into the liquid. Yeasts has 2 mayor ways of feeding. One where it produces gas - just needed inside the bread and another one with oxygen, where it proliferates and multiplies. You won't see as many action in form of gas in this stage, but later in the bread notice that the yeasts are there, and a lot.

Keeping the mother starter line alive with the formula 1:2:2 also works good for me. 26°C (78F) is the sweet spot, where the yeasts multiply fastest compared to the lactobacillii. But after some feedings at that temperature it will be more 4 to 5 hours than 12 hours, that you can feed it again (or put in the fridge, once it is that active).

speaking as a newbie, i've several times accidentally left a loaf to overproof such that it was more of a large starter than a loaf (but i baked them anyway). Those were very sour loaves. yet with the same starter i've made very light, mild loaves too. Certainly there's much to be done with the starter but not overproving a sourdough loaf could help too.