David, with all due respect, this example is bordering on absurd.
Why? Because its impossible? Or because its unlikely?
And furthermore, how would you explain all these different observations out there? Would you simply say that everyone who experiences their starter's uniqueness withering away over time with successive feeding cycles is a flat out liar? That's too easy.
Notwithstanding, it still is probably a lot less likely than you think. I have on many occasions left a starter unfed and unattended on my counter for over a week. The food supply has been completely exhausted for days, and it is full acid, alcohol and the other waste byproducts of the yeast and bacteria. That does not mean the entire flora is dead. I feed it some flour and water it will come back in a day or so and behave exactly as before (I do draw the line at mold – any mold and it’s going into the trash).
A week is nothing.
Try an entire summer in an unairconditioned place because you spend the summers somewhere else in another state. I'm describing myself there. And yes, I've had mold grow in starters. And I've resurrected starters with mold in them. Mold does not necessarily mean all hope is lost. Just dig down past the mold, grab a tiny sample, put it in a new jar, add some flour and water and within the next two weeks or so of intensive care you're back at full froth.
If you do that, is your starter going to be the exact same as it was before? That is another question. A question I feel is important and related. The very question we're trying to answer, in fact!! Some people say yes. Some people say no. Some people say maybe.
When you say adding flour introduces “the only healthy yeast in the jar,” I do not believe you are correct. The yeast cells in the flour are not healthy. If they were, it would not take a “month or two” to start a culture from them as you indicated is necessary. It would take a day or so.
I do not believe that the healthy yeast cells present within the flour need to be at high concentrations to contaminate a weak colony, which is by definition an unstable colony. You don't need a complete takeover to change characteristics. You simply need contamination to do that.
If you are correct that it takes a month or two to start a culture from flour and water, I don’t see how could also believe the yeast naturally in flour could take over an existing, established culture given any realistic set of assumptions.
With due respect to you, you should read the thread a little more thoroughly before replying. I don't feel like its that long.
I've stated, in my very *first* post AAMOF, that folks should not have a problem maintaining purchased starters so long as they take care of them properly. I've also stated, more than once, that under proper circumstances there should be no real issue with native microorganisms taking over a sourdough culture. I've stated that, so you should not be attributing alternate beliefs to me by this point.
However, I have also stated that there is some truth to the idea that starters are hardly 'bulletproof' things. 'Indestructible' is not a common description for a sourdough starter. This thread would, in fact, be the first time I've ever even seen that implied. Here we have folks literally scoffing, implying that any negative experiences reported with sourdough sustainability are utterly unbelievable!! Based on what I've seen, sourdough cultures are instead most often described as 'finicky, temperamental, inconsistent, and not worth the trouble' compared to plain yeast. In other words, it ain't exactly uncommon to have a starter destroyed and to have to replace it, or reorder another one. Apparently, though, nobody here has ever heard of that.
Lastly, I have also stated in post #19 that changing food sources can mean changing a lot. It really can turn out to be a pretty big deal. You can change an entire culture based on what you feed that culture over a sustained period of time. Switching food sources means switching certain enzyme concentrations, certain sugar concentrations, certain impurity concentrations, etc, etc in the actual food source. This means that for a given strain of microorganism different metabolic pathways now become preferred, which means that the same byproducts being produced by these microorganisms are now being produced at different relative concentrations. This alone can give the *impression* of the starter changing over time with successive feedings, even though the microorganisms actually present have not changed that much at all in terms of their relative concentrations.
Furthermore, different metabolic rates and process mean different microorganisms propagate at new and different rates, opening the door down the road for an eventual change in micro-organic concentrations. We call that evolving. Or at least one way of a colony evolving to accommodate a steady particular food source. I've actually had that happen.