The topic of selected species and strains for the use as sourdough starters is an inherently divisive one, with very little of the relevant data published for public consumption. This paucity reinforces the mythic quality surrounding sourdough cultures, lending the subject an aura that's persisted for centuries.
Personally, I am part of a small but growing movement within the professional baking and pizzamaking sector that aims to bring light onto this and many other topics, a ragtag bunch found in North America, Europe and Australia.
I invite all members of this forum to be sceptical but to remember that the burden of proof, especially on this topic, lies not with me but with those who make the ostensibly outrageous claim they can guarantee the dominance and subsequent stability of selected sourdough starter strains.
Outside of the bigger companies that produce these starters on a commercial scale, like in Germany and Italy, those who sell them lack the training, technological means, financial motivation and/or access to genomic research to even identify the microbiotic composition of the cultures they sell.
This is problem number one. The second and bigger problem, in my mind, is the ever-changing nature of the game. Particular lactobacillus and yeast isolates are being regrouped and renamed on a continual basis by researchers as the means of identification increases. This is particularly problematic for the smaller companies that regularly isolate and breed cultures; without the proper technology and guarantee of laboratory-grade aseptic conditions, cross-contamination is all but an insured end. Lastly, all sourdough cultures are in a constant state of flux, as a sourdough community is defined by whichever species or group of species are best suited for a particular sourdough matrix at the time.
“...Since these ecosystems are cultured over an extended period of time, even for years, the dynamic component is a fundamental feature of this complexity; particularly for type I sourdoughs, where backslopping propagation allows the regular introduction of water and flour but also the removal of a portion of the sourdough volume. As a consequence, the stability of sourdough characteristics is frequently disturbed. Interestingly, this dynamic perspective has rarely been taken into account in the literature. Even if an apparent stability is observed, sourdoughs still continue to evolve slowly.” +
Compounding this issue is the lack of research into these topics. The science here is very new, set atop an ever-shifting landscape as the human understanding of the microbiotic realm continues to change. This is increasingly the case in what is now referred to as the “post-genomic era” of microbiology. That we know more now than ever before still does little to answer all the questions bakers and pizzamakers have regarding the nature of their cultures.
Decades-old assumptions are being over-turned on a weekly basis, such as the idea behind geographical specificity in determining the composition of microbiotic cultures. As Luc de Vuyst, et al., writes:
“Whereas it has been initially thought that a relationship exists between geographical origin of a particular sourdough and its associated microbiota, this apparent region specificity seems to be a consequence of the interpretation of concomitant research results.” *
This new era of research is showing there is great uniformity to the world's food fermentations, especially as more and more species are discovered and their entire genomes mapped. Differences now seem to lie at the strain level rather than species.
Because microorganisms evolve at a much faster pace than the larger organisms they inhabit, backslopping enables the creation of an environment always in flux. Few, if any, bakers or pizzamakers control the wheat lots and their subsequent fraction blended into flour she uses, or assures exact temperature specificity when feeding her starter. There are simply too many variables at play for a person to control.
One industry microbiologist points out, "If you take this sourdough culture and move to Tunisia and start baking there in the ambient temperatures, if we tested the culture after a few months, we'd find something very different. The strains that currently serve you well, they would begin to be lost and other strains that are there in the background would start to do well.” &
Dr Marco Gobbetti, one of the world's leading researchers in this field, puts it more succinctly: "Yes, I know that several people claim to have stable sourdoughs for decades. In my experience, this is extremely rare.” &
In the case of selected strains for the use as starters, their stability has been called into question in the last decade's worth of research, due to the “competition between the spontaneously growing microbiota and the added sourdough starter culture may lead to the dominance of autochthonous LAB species and/or strains and hence eliminate the added started culture. This is possibly due to lack of adaptation of the starter culture to the environmental conditions of the particular sourdough ecosystem.” *
This being said, there have only been three studies published on the subject of the viability and long-term stability of selected starter cultures, all with similar results: few, if any, of the selected strains tend to dominate. (There's also a wealth of unpublished data, which I am willing to share privately, as some has not been published yet. Again, most of these researchers are very approachable and willing to answer unsolicited e-mails from the general public; contact information is available with me.)
“...Only three of the nine starters used dominated throughout 10 days of propagation carried out under rigorously standardised conditions. The others were outcompeted by the autochthonous population of the wheat flour and disappeared progressively starting from the first day of propagation . . . One autochthonous strain of L. sanfranciscensis was found to be dominant in all sourdoughs.” #
This will likely be my last post on these boards, which I have found less than welcoming. I hope those reading this keep an open mind, and, more than anything, contact those who sell starter cultures and ask the relevant questions: What is the composition of the culture (i.e., which species and strains)? What methods were used in the identification of the species? What methods were used to test the putative dominance of these species? How many trials were performed and on how many flours, etc.?
+ “Description of a French natural wheat sourdough over 10 consecutive days focussing on the lactobacilli present in the microbiota,” Leeuwenhoek et al., 19 May 2011, Springer Science & Business Media.
* "Microbial ecology of sourdough fermentations: Diverse or uniform?” De Vuyst, et al. February 2014. Food Microbiology, Volume 37, Pages 11 – 29.
& “Could the 100-year-old sourdough be a myth?” BBC Food, 16.September.2012. Angle, Emily. Weatherhill, Emma.
# “Taxonomic Structure and Monitoring of the Dominant Population of Lactic Acid Bacteria during Wheat Flour Sourdough Type I Propagation Using Lactobacillus sanfranciscensis Starters.” Siragusa, Sonya, et al. 2009, Applied Environmental Microbiology.