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Hi Melissa–there is a now-classic, still ongoing microbial evolution experiment by Dr. Rich Lenski that will support what you found about the unique evolutionary trajectory of your sourdough microbes. Also Dr. Athena Aktipis, also an evolutionary biologist, has done a similar tracking of Kombucha microbes.
Readers here may enjoy finding out more from this conversation with my fellow evolutionary biologist and husband Dr. David S. Wilson
and in the paper Kombucha: a novel model system for cooperation and conflict in a complex multi-species microbial ecosystem [PeerJ] from Athena.
Anne
Great experiment Melissa! Your results tend to confirm what I saw last summer when I made 2 starters using basil water using leaves from the same plant but one started with normal filtered water and one started with an acidic lemon water mixture. They each had subtle differences in doubling time, aroma and flavor.
My guess is that at the beginning, there are many bacterial and fungal flora in the starter that are vying for supremacy. The combination of that flora, the environmental conditions, the food source (and perhaps a roll of the dice) favors the winning symbiosis of bacteria and yeast once the starter hits equilibrium. Like snowflakes, each starter is unique.
I am also intrigued by Gerard Rubaud’s habit of beginning a new starter every few months. One would have thought that once you have a successful starter, you are good to go and just need to keep it well fed. Perhaps he was trying to encourage new, robust starters that gave a more complex flavor profile for his much sought-after breads.
Also, I think you can alter the equilibrium by changing how you maintain your starter. For instance, if you maintain your starter by feeding and refrigerating it, you may favor a certain subset of strains and may lose some of the diversity in your starter. I noticed that my basil starter became less explosively active and the flavor was less fruity after I switched to the feed/refrigerate method. All interesting stuff.
Keep up the good work Melissa!
Without looking under a microscope it’s practically impossible to know what is causing this change. Is it the characteristics of the flour itself? Or have you just encouraged more of a yeast or bacterial ferment as supposed to actually changing them?
My question is… It takes sometime for the yeast and bacteria to establish themselves when making a starter from scratch. Once a starter is strong and stable they outdo any invading bacteria due to its symbiotic and acidic nature. In other words they’ve set up home in a way which makes themselves flourish and keep others at bay. Plus it takes time for them to do this. So why would any invading bacteria take hold? The only way I can think of is if something goes wrong with the starter and it takes time to get it back to health. This is a window for which a starter can change.
Great experiment and useful information!
One observation I would make is that your 1:1:1 feeding procedures is on the starter-heavy end of the spectrum. Many feeding procedures use way less starter, for example the one from the Rye Baker that I use with my rye starter is 1:10:10. Surely 1:1:1 favors the stability of the starter’s microbiome rather more than a “less starter” procedure.
It would be interesting to conduct some “starter battles” with your two starters. What would you get if you made a starter refresh with mostly one but with just a touch of the other? What would you get if you did a 50/50 refresh with the two? Would the majority always win? Would one always outcompete the other? Would you get something different from either?
Good point Eric. Many bakers stick to a lower starter refreshment for this very reason.
Hello Melissa,
I have been baking all our bread for the last 2.5 years with a starter I made from scratch originally using rye flour. I’m not systematic in following recipes and have fed my starter a variety of whole grain flours (1:1:1) over this time, but haven’t used rye in about 2 years. Never used AP. Its smell and consistency are constantly changing but I never attributed this to the flour. Six months ago it definitely had an acetone odor but for the last couple of months (I think I’ve been using spelt flour to feed it) it has a wonderful fruity aroma.
The bread I bake usually turns out well although the oven spring is not as high as in the first heady days of baking my own bread. Perhaps this is because I’m not as conscientious about following a consistent stretch and fold regime. I now wonder it it has anything to do with the starter.
Kitchens are not Level 3 Biosafety facilities and no culture is safe from contamination. For example, from the baker’s hands! https://journals.asm.org/doi/full/10.1128/mSphere.00950-19.
Sourdough starter cultures made at home have been followed serially and they change constantly. Sourdough starters vary regionally around the world. As with wine grapes, the naturally occurring wild yeasts add to the microbial diversity. As as for the bacteria…well, lactobacillus species are found in the intestines of animals. Those animals defecate. The entire world is covered with a fine patina of poo. Within the poo are microorganisms, and when the wind blows that micro-poo winds up covering the wheat and rye and everything else. My favorite sourdough bacteria is Lactobacillus reuteri, which comes from pig shit (mostly).
The specific microbiology of commercially produced sourdough and yoghurt is too important to leave to chance. Can you imagine a bad batch of Dannon yoghurt, all 10,000 gallons of it?
All bacteria, including lactobacillus species, are susceptible to infection by viruses (known as bacteriophages). Yeast (a complex single cell organism with a nucleus and a pretty impressive immune system) is also vulnerable to infection by viruses. At large commercial enterprises, microbiologists track the cultures and stand by if a phage virus wipes out the lactobacillus. All most home bakers can do is sniff the aroma from the culture vessel.
Food scientists have compared the flavor and texture from many different bacteria; in one study, a particular strain of Lactobacillus reuteri was clearly the most sour. This reference strain is available for purchase from a microbiology library for around $500.
https://link.springer.com/chapter/10.1007/978-1-4614-5425-0_4
@AnneClark Thank you for sharing those two articles. Your husband’s interview of Dr. Lenski describing the 12 e.coli populations that have some parallel evolution but also relatively independent trajectories is really interesting. Based on his research, can I extrapolate that a sourdough starter simply divided into two jars and fed the same way would end up diverging with enough time? The Kombucha article is neat too. Reminds me of the microbial interests that eventually led me into sourdough baking: learning about the cooperative and competitive behaviors of microbes in the compromised human lung. (Concurrent gut dysbiosis came up enough in that reading that I started fermenting things.)
@djd418 Your description of all the elements that come into play, including the dice roll, sounds right to me. That’s interesting about Rubaud’s preference for making a new starter every few months, and your observations about feeding and refrigerating. My starter does spend a lot of time in the refrigerator, but it also comes out to room temp because in my no-discard approach, it’s my levain building jar. Every bake is a feeding and ripening of the mother at least once.
@ericjs and @Abe Good point about the feeding ratios and starter establishment. I only did the 1:5:5 feedings on the rye convert starter twice at the beginning to eliminate the AP flour. It will be interesting to see how the two starters evolve as more time passes.
@apregenzer My old and new starters had the same oven spring, even in that week-4 test bake when one starter was lagging in the jar after being fed. So maybe I’d go with your theory that you could be doing less gluten development these days? Or the heat of summer is over proofing your dough a little.
@ashley4syth Those are cool articles. Thanks for sharing them. The one on L. reuteri especially, makes me think about how sourdough fermentation is digestion outside the body.
This info in the conclusion of the pdf is also interesting and helps explain my observations about sourness and fermentation duration and temperature; my mental notes have felt all over the place. Now I can see if they fit into the categories of:
early first 24 hrs of fermentation, if extra hot, then more sour
late after 24 hrs of fermentation, if cooler, then more sour
I do wish the temp info was 25C vs something like 4C (refrigerator temps).
At the start of fermentation, sourdough fermented at 25°C had higher pH values than those observed in batches of dough fermented at 35°C and a slower increase in acidity. However, after 24 h the development of acidity was slightly greater in dough fermented at the lower temperature. In parallel, the counts of LAB were marginally higher in sourdough
fermented at 35°C at the beginning of fermentation…
I agree about the temperature dilemma.
By the way, I ‘cheated’ and bought L. reuteri online as a “probiotic” preparation (for human consumption). I opened one capsule and dumped it into a new sourdough starter and voila, I had a great starter. It is indeed the most sour tasting bread I’ve ever made.
At the beginning of the pandemic all of a sudden there was a shortage of yeast. Everyone was panicking. Of course it was no problem for all those who already were baking with sourdough and that is why sourdough had a revival.
Even though I very rarely, if ever nowadays, bake with commercial yeast and don’t keep any in stock it got me thinking. One couldn’t find yeast in the shops but why not in health stores and being sold as probiotics? And sure enough there was plenty of yeast if you knew where to look. S. Boulardii is a yeast almost identical to S. Cerevisiae (in fact it is often thought of as a sub species) and it’s a probiotic. Quite a bit more expensive than buying bakers yeast but one capsule is enough for a poolish and another in the final dough if wanted.
Makes a lovely bread just like baker’s yeast.
An idea… Why not combine S. Boulardii and some Lactic Acid bacteria of your choice to make a quick sourdough? CLAS is very much the same thing. A Concentrated Lactic Acid Sourdough, with just the bacteria and inhibiting the yeast, is made in a relatively quick time then it’s combined with bakers’ yeast.
How much time does your starter spend in the refrigerator and is this fairly consistent and how often do you do really high ratio feeds or have you ever washed your starter (as per the sourdough library) to reduce acidity ?
I ask because I am nearly certain that over time several things occur that start to erode the gluten in your dough more so than in the beginning. Also, over time what I’ve noticed I do is not get too much in a hurry and let doughs ferment a little longer, kinda like a mother worried less with her 3rd or 4th child maybe, sort of. I have had my starter for at least 20 years. It does best if I really ramp it ip with high feed ratios and warm temps.
If I dry it and reconstitute it it works a lot better too. Just some thoughts.
Other things that can occur over time are build up of thiols from dead yeast cells, increased acidity and bacterial colonization, and build up of protease. All gluten killers.
Wonderful experiment Melissa, well designed and such interesting findings. I’ve always assumed that the microbes in the starter would, over time, gradually shift towards the microbes in the flour it was being fed. As others have pointed out, that might be more likely for those starter being given very high ratio feeds regularly rather than smaller feeds such as 1:1:1 which would favour the existing microbes. I hope you keep reporting back on your findings, they are truly exciting.
I applaud you for your methodical approach in such a painstaking experiment. There is so much contradiction in this science of sourdough. Most conventional wisdom, and I think a lot of it comes from Harold Mcgee’s summarized research, is that no matter what you start with, eventually a culture will take on what is in the surrounding environment. I think this still has yet to be proven. I am not sure 6 weeks is enough time to prove that it doesn’t happen, it is also well known that how you feed and incubate your starter can have a significant influence on the flora make up, sensu Debra Wink and all of her writings in the Fresh Loaf and contributions to King Arthur.
I have had my starter going since about 2000, I’ve kept it going for twenty years, and i kept it the refrigerator a LOT. I am not rigid in my feeding and incubating regimen. (I do not qualify as a contributor to the Sourdough Library unfortunately.) I do recognize that I have the ability to change the smell, taste and performance of my starter though. The most striking difference I made was taking some dried starter to California with me and I started making bread for myself and friends there, I noticed my dough was much livlier, easier to handle, I had great spring and great flavored breads! I can’t say it was the environment, the climate, or even the flour really (I was using King Arthur, which I often but not always use at home). I am also curious about the above poster who mentioned that Rubaud starts new starter, this makes sense to me to a certain extent, but I’m not sure he really has to. Karl DeSmedt even says that over time a sourdough gets acidic and needs to be “washed”. There is just so much we don’t know, but hopefully somewhere a long the line, in my lifetime someone will provide a solid compendium (that is presentable to the average home or semi-professional bread baker) on how sourdough lives and breathes and is influenced by human input.
@Abe and @ashley4syth Those are neat ideas. Also perhaps using purchased bacteria or yeast could be a way of backing into the identification of what’s in your starter. Maybe. If you’ve got a “super taster” palate. I think I have more of a regular taster palate.
Thanks @Benito and @muchohucho I’m definitely going to continue carefully feeding the two jars of starter and baking with them periodically to see how the flavors, colors, general feel of both continue to evolve. I just fed everyone yesterday, making two doughs with all the discards. (I need to get into a cracker habit!) My regular starter is like yours @muchohucho – fed and incubated in a million different ways. When I bring it to a Rhode Island beach vacation, it goes nuts with activity. Maybe an ambient humidity thing. I actually feed it chlorinated tap water there 
and at least in the short term, this isn’t a problem.
Feeding everyone yesterday 
How about one bread two pre-ferments? Hamleman does this for his durum bread but one is a biga and another a levain.
What if it’s a full sourdough with one biga type levain fermented at cooler temperatures. And another high hydration levain fermented at warmer temperatures.
Maximizing both the yeast and bacteria in your starter? Best of both! Since in a starter the bacteria roughly outnumber yeasts 100:1 i’d probably make the biga a higher percentage.
And building on this idea CLAS goes further building a starter with only bacteria by fermenting at much higher temperatures in an oxygen deprived environment. Then it’s used in a bread recipe with bakers yeast. Working with an established starter one can replicate this with no extra yeast needed. Two preferments with your starter. One a low hydration biga and another very high hydration, at temperatures which suppress the yeast, oxygen deprived (covered with plastic wrap) all encouraging the existing bacteria.
Yeah, a lot of traditional rye breads get the 3 stage ferment to accent each microbial group (lactic, acetic, yeast).
Thank you for reminding me. I’ve seen these three stage ryes. Detmolder? Can it be done with wheat? do you have a recipe?
I think i’m going to do more experimenting along these lines.
I have Dan Leader’s book Living breads and he doesn’t call it by name but that’s basically included in some of the rye recipes, and its apparently in Hammelman’s book, which I don’t have, but its parapphrased here: Detmolder 90% Rye Bread | Beginning With Bread
and yeah, I’ve started in on working with rye’s now that I bought 25 lbs of berries when I only wanted 5. I have eschewed rye breads mainly cause I don’t like the stickiness but make Eric’s version of Swedish Rye for a few customers (I have an extremely small “business”). But that recipe is more straight forward levain-wise.
Thank you for the link. I have Hamelman’s recipe but i’m wondering if one can follow the steps with wheat? If I take the technique and method but make a wheat sourdough will I get the same effect. I wonder why this method is more common with rye?
