Prefermenting the whole sourdough rye bread

I am still very much an amateur in this area, however my current mental model is that the way to develop more flavor is by slowly cultivating many generations of yeast.

So, the potential problem with letting your young yeast get all the sugar all at once, is that you greatly reduce both the time and the number of generations.

• One option is let your yeast multiply in a small portion of you total dough before it joins the rest of your dough.
• Another option is to let your yeast multiply under refrigeration.
• A third option is to do both.

There are several reasons you only ferment 30% - 50% of the flour:

You can already mix all the water with this comparatively low amount of flour, resulting in a more mild (less acetic acid, more lactic acid) bread. It also helps getting more yeasts.

There is a danger the bread will ferment too much. Once you reached that point, there is nothing you can do, except doubling the amount of bread you make by adding more flour and water :). If you bake it anyway, it will collapse in the oven and be wet inside. The reason is that fermenting it is effectively using up the starch in the flour, which binds the water and provides structure in the bread.

If you ferment only a third or half the flour, even if you let it ferment too long and your yeasts in there starve to death, you can simply add the rest of the flour and some yeast afterwards since there will be enough starch from the new flour to provide food for the new yeast and structure in the bread.

It is certainly possible to ferment all of the dough and make a good bread from it. You typically do this to wheat breads because rye breads simply taste too strong when made this way. However, the margin for error is very small and I would recommend you get some experience with the "usual" way of making sourdough bread first.

First, you have to differentiate between "guiding" the starter and making a preferment for flavor purposes. A sourdough starter colony is not in a bakable state, its population density is wrong. It needs a few hours in a specific environment (sufficient food, etc.) to "revive" and get into a state which will work in bread. This is different from making, say, biga for white yeasted bread, which just tries to create a bit of yeasty flavor, disregarding culture viability.

I am not sure you can bake with guided starter only, without adding more fresh dough. Sourdough making stages are optimized for the best leavening power, and it is likely that, if you don't add more fresh flour and water after the preferment has become "ready", it will not perform well but start to go into an overfed stage, without much leavening power. This is a bit of a conjecture, as I have not worked with rye sourdough starter.

Second, preferment is not dough, and it handles badly. It lacks the elasticity and suppleness of freshly made dough, so even if you can get proper leavening action, it cannot make a nice loaf texture.

The "too sour" argument is actually a matter of taste. I am certain that, if a lot of fermentation produced the best bread in terms of leavening/texture and durability, people would have grown to regard very sour bread as the norm and enjoy it.

If you really want to try baking with pure firm preferment, nothing stops you from trying. It is likely that you will like the result less than properly made bread though.