I wonder if you can expand on this tip of using 0.3% fresh yeast combined with 9-10% natural starter. I believe I have read that when you combine commercial yeast with natural starter, the commercial yeast will "take over" in the fermentation process and overpower any fermentation driven by the natural starter.
Is that correct? incorrect? Is the combination for flavor only? , etc.
Also, given the two are present, how would I rethink the timing of the dough. Would it be ready sooner?
Thanks in advance,
Co-ferments are a nice way to achieve great flavour and texture, even more so than commercially-yeasted preferments, which add little to a dough, in my opinion (especially pizza doughs). Even though I do not use them myself, I think the resulting doughs are infinitely preferable to anything achievable with industrial yeast alone.
There are a few topics I can address here.
First, whenever commercial yeast is used in conjunction with sourdough in an intermediary or final dough, the fermentation should be categorised as yeasted, and the addition of sourdough should be viewed as a natural dough improver only. Industrial yeast has shorter generation times than sourdough microbiota and will easily out-compete in most normal dough circumstances, except those with a very low starting dough pH (say, under 4.0)--an unlikely consideration.
Second, the natural starter is added as a natural dough improver, creating better preservability, flavour and texture, although not to the same degree as a dough leavened solely with sourdough. The inclusion of starter does add to carbon-dioxide production as well, cutting total fermentation time by approximately two-thirds.
Third, given this last statement, it is then necessary to re-jigger normal leavening amounts found in formulae. In continuously-maintained sourdough starters, both yeast and heterofermentative lactobacilli create CO2. By adding a third leavening agent to the mix, fermentation will occur at a rate approximately 1.5 times faster, so it is preferable to reduce normal inoculation amounts--of starter and IDY, both--by two-thirds to achieve the normally-desired results. (There has been a spate of dough formulae in recent years that have won the best baguette in Paris competition using natural starter and commercial yeast, and all hover around 9 - 10% of the total flour prefermented, with good reason.)
For IDY and natural starters, I would recommend a FDT of between 22° to 25°C and a total bulk fermentation time of 3h. For optimal flavour results, I would also recommend not going over 2.4% salt, as any more negatively impacts the aromatic contribution of what is already a minor lactobacilli presence. The dough can then be retarded in shape.