She keeps a jar of sourdough starter in her refrigerator that she says is descendent from our relatives who lived in the colonies.
She'll bake something with this sourdough starter, then return a little bit of it to the jar, as she says her mother, grandmothers and aunts did before her, all the way back to the 1600's.
Thus, she concludes, her sourdough starter is essentially (and I guess, elementally?) the SAME LIVING STUFF that has been in our family since the boat.
Question: she's a sweet lady, but prone to exaggeration for a good story's sake...so is she B.S.'ing us?
I wouldn't say she's necessarily full of crap, because it's certainly possible to have a sourdough starter live a very long time under the right conditions. I've heard of Parisian bakeries claiming to have yeast strains that go back to the Revolution. On the other hand, that's a very long time for it to last, and everything I've read from British bakers in the nineteenth century suggested that yeasts and barms were very finicky creatures and that they were known to go very sour--unpalatably so--at a moment's notice and for no immediately obvious reason.
So, I wouldn't be surprised if your grandmother did have a quite old starter, but I think it's unlikely that it's quite that old.
hi! It might be worth x-posting this to a cooking/baking sub (/r/AskCulinary?) or specialist bread sub (/r/Sourdough? /r/ArtisanBread?) for their input. There is a bread historian here who hopefully will drop by, but meanwhile, you may be interested in some earlier discussion on sourdough
This isn't a history question but I happen to know a fair bit about sourdough so I'll answer this one.
A starter is a colony of micro-organisms containing different species and different strains. Sourdough starters are a symbiotic colony of both yeasts (which produce much of the CO2 that provides the leavening of the bread while it rises) and lactobacilli (which provide the acetic and lactic acids that give the tangy flavor to sourdough breads). The acid produced by the bacteria helps keep out other bacteria, fungi, and other sources of microbial contamination. In general there won't be just one strain of either yeast or lactobacillus in the starter, there will be a population of several in varying populations. Additionally, over time other yeast and lactobacilli strains will enter the starter through the air or on the flour used to feed the starter. Sometimes they may die off due to being less suited to the particular conditions of the starter than the existing population, other times they may displace the existing population and become dominant. Realistically the expected case is somewhere in between, with perhaps a slight "demographic shift" over time of the starter population due to environmental micro-organisms coming along. Additionally, the starter will be subject to selection pressures, and the traits of the population will be pushed towards being able to survive better in the conditions at hand.
Overall, if the starter has been faithfully maintained continuously there's no reason to assume that the current population would not be substantially made up of descendants of the population from the 1600s. But there's no guarantee that's true either, it could potentially be primarily yeasts and lactobacilli from the environment or the flour that are unlike those from the original starter.
This is more of a philosophical question than a historical question.
It is clear that (if it is true that the starter dough has had a continuity for decades or centuries) the original dough has been removed and replaced, with only a tiny fraction of the original returning to the mix each time until the levels of original dough are at 'homoeopathic' levels (1 part per billion or higher).
Thus there is no meaningful physical continuity, but the idea of the bread starter has been in continued existence, though ever changing.
Thus it is your choice whether to accept whether the 'ideal' continuity has meaning or not when the physical continuity is essentially meaningless.
For the origins of this debate see the 'Ship of Theseus' http://en.wikipedia.org/wiki/Ship_of_Theseus
To answer your question: In the tradition of the best philosophical questions, yes and no.
It's the strain of bacteria that continues to live. Technically, she's not full of crap (assuming the starter's origin is true).
There's a bakery in San Francisco that also makes claims about using the same mother dough that was first used in the 1800s:
Today, the Boudin family's initial recipe lives on in the hands and hearts of our expert bakers, with a portion of the original mother dough still starting each and every sourdough loaf we make.