The Fresh Loaf

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Thoughts on starter stability

Doc.Dough's picture
Doc.Dough

Thoughts on starter stability

Since the facility to accept text from Word documents is not yet implemented here, the text of this post can be found at this link.  The figure below is notional but while it does not reflect lab measurements, it should be thought of as an aid to thinking about the underlying issues.

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msneuropil's picture
msneuropil

Perhaps this is a stupid question...and I did look at the link just to see...

But which is A, B and C??   Laugh if you must....but I didn't sleep tonight, which is why I am here reading...and it seems I need that info to understand your graph.  I *think* it is in the document...but not sure if I understand it.   LOL!   I am particularly interested in which one is salmonella for a nerdy reason. 

 

 

Doc.Dough's picture
Doc.Dough

(which you can find by following this link), and think about how many yeast and LAB species they found in each starter sample they tested.  Every one of those is a candidate to out-compete the primary species (and of course all of the other "contaminants) in the sample. You can think of A, B, and C and notional contaminants.  One point that can be inferred from the figure is that if there are contaminants that grow to a larger population density than the primary species during your refresh cycle (for any reason but most definitely because you deviated from the most recent prior cycle) then they may continue to out compete the primary species on average over many cycles going forward and eventually displace the primary species.  They may have different temperature sensitivities. They may depend on nutrients that are not consumed by the primary species. They may be in your starter as minor constituents, or they may have come to the starter as contaminants in your flour.

But for any species that does not return to the pre-refresh population density, your primary species has gained a numerical advantage.  This goes on for every refresh cycle. And you don't know what is going on in your starter.  So it is a good idea to use exactly the same refresh process every time, because that is the only thing that assures that your starter remains stable.  In fact that is a little bit of overstatement since the flour always brings some contaminants to the mix, but you still don't want to amplify them.  Stability is defined by consistent refresh cycles.  Anything you do moves you to a new starter with a different vector of species populations. If your starter and refresh process are not compatible, then your starter is not stable.  A more stable starter will remain close to the original species vector over a wider range of variations in your refresh process.

I suspect that most starters are pretty stable (in the sense that small perturbations in the refresh cycle don't allow any contaminant species to out replicate any of the primary species) and thus tolerate some level of abuse.  But if you allow a contaminant to get out of control, you have no path back to where you started.  If that happens, the best advice I know of comes from Mini Oven: –– to switch to a 5:10:15 refresh at room temperature and repeat when if falls back. And if that doesn't work, start over.

msneuropil's picture
msneuropil

Thank you.  My concern really wasn't so much controlling the contaminants... for I've been surviving sourdough starters for 50+ years...without much of a problem at all.  

My curiosity was due to my interest in microbiology and how those contaminants are controlled by the acid environment.  For example...recent recall of flour due to Salmonella.  I wondered IF someone used such flour...and over long period of time of refreshing...IF the Salmonella bacterial load increased or stayed stable.  Not a personal concern of mine for I don't use that recalled flour...

I just am a bit nerdy...

I just was wondering, in my way,  IF "A" was salmonella...vs "B" being Ecoli...vs..."C" as coliform... (as an example based on your document and my assumptions) then one could perhaps say that salmonella was NOT multiplying in the acid environment.

I suppose all is moot since if you bake it...and it tastes good and you survive...all is well with the world.  As long as your washing your hands and equipment then "raw" sourdough shouldn't be a risk.  But I have to talk to my granddaughter about her tasting raw bread dough...despite my warning her in the past.   

I understand why one wants one or the other level to keep their starter where they want it.  Your graph just got me wondering and I am an analyser personality...and my greatest need is to know why "C" stays stable.  LOL!

Doc.Dough's picture
Doc.Dough

So long as the cyclic gain is less than 1.0, then population density at the end of the refresh cycle is lower than it was in the seed, and the contaminant is becoming less of a problem with each refresh. While there are salmonella varieties that are acid tolerant, they don't originate in wheat and are rarely an issue except when a batch of flour gets contaminated from an external source.  But if it didn't kill you the first time, it probably won't kill you after that either if the population density is going down every time you refresh. Use clean containers, potable water, and good quality flour, and refresh often and your starter should outrun any contaminant.  If the net population density reduction per cycle is 0.5, and you refresh twice each day for three months, you have (0.5)^180 or 10E-55 of the original contamination level.  So ten days at two refreshes a day would be more than you would need if this model is accurate (which it is not).

msneuropil's picture
msneuropil

I was just curious.  I don't eat raw dough...but I just watched another video of a guy tasting his sourdough starter...LOL!  Makes me crazy when people do that...but I'm a little OCD I guess.