May 22, 2018 - 10:57am
Double Levain Formulas
Hello. I see a number of formulas in various threads on TFL which call for double levains - that is, two levains prepared separately but simultaneously for a single bread. For example, there are many, many iterations of Pan Maggiore here which call for a rye or whole wheat levain plus a white levain, or some similar combination. I’m wondering – is it necessary to prepare these separately? Is there any reason why it couldn’t all be combined, in the correct percentages, into a single levain? Maybe it’s chemistry, or maybe it’s just tradition. But I’d like to understand it better if anyone has an insight. Many thanks.
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If one of your leavening agents is a white flour biga or a poolish, and the other is a 60% hydration rye levain.
That’s a grest point alfanso. In this case there were two sourdough levains - one made with rye starter, water and whole wheat flour, and the other made with rye starter, water and white flour. It was the same rye starter in both cases so I couldn’t for the life of me figure out why it couldn’t all be combined. And I’ve come across a number of formulas like that.... Mysterious.
There is a phenomenon well known to microbiologists called diauxic growth. This occurs when a microbial population is fed multiple carbon sources. Some will be "preferred" by the bugs more than others. They will take off proliferating on the "preferred" source and will then slow down as they shift to the less preferred source, with a measurable reduction in population growth rate seen during the shift (there is a proliferation rate cost to re-tooling their metabolism to the less-preferred source). This may or not be relevant to your question, but microbial populations do have more and less preferred carbon sources. Keeping levains separate in double levain formulas allows the starter cultures to maximally process each set of substrates, and not serially move from one to the next in the same culture. Metabolizing the preferred substrate in such a mix might alter the growth medium (e.g., acidify it) in such a way that the less preferred substrate might not be metabolized in the same manner it would have, had it been supplied separately.
Again, I don't know how relevant these phenomena are here, but they would certainly come in to play in double versus combined levains. If you are inclined to experiment, it would certainly be interesting to prepare two doughs with the same overall levain components, one with a combined, single levain and the other with the two grown separately in the double levain fashion.
Tom
That is really fascinating Tom. This is an area I know nothing about, and I appreciate your insight. Yes, that might be exactly what’s going on, and it might explain the need to keep the levains separate. I think I will experiment as you suggest – one combined and one separate – and see if there is a noticeable difference in the final product. I am always amazed at the breath of knowledge of folks here on TFL. Many thanks.
Thinking about this in the night, I fear I have misleadingly oversimplied the complex ecology of SD cultures by invoking the diauxic growth phenomenon. While it certainly applies, in terms of the metabolic regulation occurring in the SD culture's microbes, diauxie was recognized and has mainly been studied (by Jacques Monod, in one of the most important experiments in the history of biology) in the bare bones context of one microbial species (E. coli) and two metabolites (classically glucose [preferred] and lactose [less preferred]). However, in an SD culture, you not only have multiple microbial species (both yeast and bacteria) but a dizzyingly complex growth medium of suspended flour[s] consisting of dozens if not hundreds of metabolizable compounds. The resulting interaction of species and substrates exponentially complicates the biology (as much ecology as microbiology) and, ultimately, the impact the levain can have on the structure and flavor of a bread.
Tom
- one with my normal rye based culture and the other with a kefir based culture. The kefir levain was intended to boost the taste (sour) but if I'd mixed them both together initially, the kefir culture would probably have been swamped by the rye culture.
Hamelman has a double levain durum bread. One sourdough preferment and another yeast preferment. I suppose for obvious reasons you'd keep them separate but the final bread is a hybrid.