Why won't my sourdough form a shapeable dough that doesn't stick?

When I was young and poor I baked all the bread my family of 5 ate, for several years. I baked yeast and sour dough breads with various flours. So some hints: 1. Use good bread flour! King Arthur's or Hecker's brand, if those are not available look for a high gluten wheat flour, if possible unbleached.
2. Get good at making yeast breads first. Yeast is more efficient than lactoacid bacillus and will make bread rise better. Once you have made a few batches of nice home style white, then try adding in some different flours. I used to make oatmeal, rye and Anadamer bread. All of which are variations on white. None of them will rise as well due to the lack of gluten. Then add your sour dough to the yeast dough. Yes, you can get sourdough to rise without yeast but it will take much longer and occasionally fail. Adding the sour dough starter to a yeast dough will still get you the great sour flavor with the bonus of a better success rate.

3 There is no substitute for kneading. You generally can't stir enough flour into a dough to make a firm bread, you have to knead in the last couple cups. Your problem really sounds like not enough flour being kneaded in at the end. Your boule should be smooth and have a dusting of flour on the outside. You can over knead, if the dough starts to tear rather than stretch just let it rest for half an hour.

Ok, I've looked at your links, and have a few suggestions that might help. You mention using a mixer and dough hook for the initial kneading. This might make a big difference in your dough coming together, especially since the video emphasizes the kneading method (the folding-over technique) shown in the video to develop the gluten.

The video specifically cautions against using flour to make the dough less sticky, instead of kneading enough - which means the dough is supposed to be very soft and sticky, and it is common enough for people to treat it as a problem - and adding more flour will not give the results they want. The dough hook may not be kneading enough, so you underestimated the amount of time you needed to knead afterwards... or it might take more kneading because you used the mixer, I'm not sure. Just keep kneading until the dough comes together, and you can tweak the recipe (or pick a different one) after you've made it work the first time. You might look at other questions (like this one) for tips on how to work with very soft and sticky dough.

Another point that might be relevant is the flour mix. The video used both bread flour and whole wheat, in the starter and in the dough - which is fine, but a problem might come in because he mentioned several times that the mix was optional, and could be made with either flour or any combination of the two. If you faithfully used the exact same mix for the starter and dough that he used, then the procedure should work exactly the same way - but if you customized your flour mix, as he encourages, you will end up with a dough that's a little bit different, and might (for example) need to be kneaded a bit longer to develop like the dough shown in the video.

Possibly even if you used the right ratios of flour, a difference in brands or quality might make a difference in your dough's moisture level. This video depends on interacting with the dough and watching its development, which lets the recipe be a bit looser and less exact - but if you're sticking strictly to the timeline, a slightly different flour mix might throw you off.

Along the same lines, there's a couple places where more water is added to the dough, when he uses it to keep the dough from sticking to his hands or to the spoon during the initial mix. It shouldn't be enough to throw the dough completely off recipe, but changes like that can help add up to a bigger effect. I once had an issue with my bread, where I had replaced part of the flour with gram flour, which threw off the moisture balance - and when I tried using water rather than flour against sticking the combination had the bread melting (well, flattening) in the oven before it could bake, since it was too, too wet. A couple small changes can stack up, especially if you don't think to compensate for them.

Had the same problem. It was fixed by adding more stretch–n–fold action intermingled with resting. Dough likes time and patience. If it is still too sticky – repeat. Then dust it with flour and give it a final rise in the bowl. (Dust the bowl generously too).

You will end up with crust slightly more dense with flour then the inside of the loaf. That density is what prevents runny dough from sticking to the bowl.

Empty the bowl immediately before you score and place it in the hot–hot oven. At this point, even if it is still look a bit flat, it will rise to form a nice boule – due to the additional air bubbles you incorporated during stretch and fold.

In addition to the other comments, it is important to bear in mind that sourdough is a mix of bacteria and yeats that perform both lactic and alcoholic fermentation.

In practice, this means that as the fermentation goes on, the pH of the dough lowers, triggering a digestion of the gluten network developed during kneading. As the gluten is digested, the elasticity is lost and your dough becomes liquid-like pancake batter. It is unavoidable.

The question "how long does it takes for my dough to become liquid" depends on several factors, many already raised above:

• Flour protein content. Stronger flours (i.e. more gluten/protein) develop better elasticity.
• Temperature of the environment. If you leave your dough next to the radiator it will ferment much faster than if you leave it in the fridge.
• Initial quantity of sourdough you use.
• Initial ratio of water/flour in the dough.
• Kneading helps to develop a stronger initial gluten network.
• Stretching and folding helps to develop extra elasticity during.
• Strength of your sourdough. Healthy active sourdoughs work faster.

There is no "ideal" way of dealing with these factors. It all depends on which result you are aiming and how much time you have to assist your dough. If you have time to keep track of the fermentation, you can do stretch and fold and feel the consistency. If you do not have time and want to leave it unattended, you could either do an initial stiffer dough or reduce the initial quantity of sourdough in the mix. Of course, all these three will lead to slightly different final results. But this is the magic of sourdough!