where does "native yeast" actually come from?
I posted this question as part of an answer in another forum, but it really belongs here.
Are these native yeasts we use for sourdough actually from the surrounding environment, or are they perhaps just hiding in the wheat, deposited there in the field or in the mill? That is, are they really native to my kitchen (in Texas), or maybe native to somewhere like Montana, where my hard winter wheat comes from?
I suspect there are yeasts from both places that end up in my sourdough, but it is by no means clear which one is dominant. I guess if one wanted to ensure that local native yeasts were dominant, one might sterilize the flour, perhaps by hydrating it with chlorinated water, and just letting the chlorine evaporate. To test for flour-resident yeast, could just cultivate the starter with flour and water in a sealed container, and see if anything grows. Anyone done these things?
Would be interesting to be read something for bakers about native yeasts for bread from a yeast biologist. Anything out there in the literature?
Doug
I always grow starters (from scratch) in sterilized and closed containers and they always thrive, much more if the flour I use is wholemeal. Moreover, if the flour is freshly milled the starter takes less time to activate.
In my opinion this is an evidence that there are yeasts in the flour, not willing to say that there aren't in the environment.
I'm eager to read Debra on this subject.
Yeast are like bacteria: they are everywhere. In/on the grains, in the air, on your skin. Everywhere.
I'm convinced that if one were to sterilize a batch of flour, and leave it in the environment, it will eventually become populated with enough yeasts to culture.
Of course I do believe the yeasts are already primarily in/on the grain. That has been already demonstrated, I believe.
Just my gut feeling, and a somewhat educated guess.
Thanks. That makes sense that the likely source of the natural yeasts is where the flour came from, which is probably not local. I have no problem with yeast appearing that way, but there are people who are very proud of their own sourdough yeast that they assume comes from their back yard, or from wherever they first made it. Makes one wonder if SF sourdough yeast really has anything to do with SF! I absolutely agree that the right way to be confident about having local native yeast is to sterilize the flour before you leave the batter out to gather those local yeasties up. Hardly seems worth the effort. It's also clear that the top of my refrigerator or my front hall is as good a place to get seeded with natural local yeast as my backyard.
Makes one wonder if SF sourdough yeast really has anything to do with SF!
Yes it does. The classic San Francisco culture is a yeast often called Candida milleri and a microbe often called Lactobacillus sanfrancisco.
My impression (sorry, no evidence:-) is that San Francisco is somehow a special case; that that sort of close association between a particular location and a particular starter culture is the exception rather than the rule.
(I know from sad personal experience that San Francisco residents who create their own starter culture these days often do not get classic San Francisco sourdough:-)
This bacteria isn't tied to location. Quoting:
from http://www.thefreshloaf.com/node/10375/lactic-acid-fermentation-sourdough
The methods they use are handed from baker to baker as are the starter cultures.
The yeast strain may be particular to the grains grown in and around the area, I won't argue with that, and that will certainly modify some aspects, but the bacteria is everywhere.
Recipes for making your own sourdough urge you to put the mixture by an open window or even outside to "capture" the wild yeast. Research has shown that the yeast are already present in the flour, though you certainly do "capture" some local yeast in the environment as well.
What I haven't seen are studies to show if certain particular strains of yeast are "stonger" than others, so that if you do have a particularly "strong" strain of yeast locally it will eventually make up the larger percentage of yeast population in your starter.
And remember that it's not only yeast that contributes to sourdough flavor, but also the beneficial bacteria. I"m sure that hitches a ride in on the flour as well, but maybe the local bacterial flora have more to do with the flavor in the end???
Excellent point about bacteria. As noted above Debra Wink has some good insights here about the roles of both bacteria and yeast in creating flavor. Does she have a book?
It seems that indeed, some strains of yeast are stronger than others. As a result, if you get yeast from somewhere else, and use it for a while without some kind of antiseptic protection, it will likely get taken over by local yeasts. I was gifted with some well used and propagated sourdough starter that originated, I was proudly told, fifty years ago at a South Dakota mining camp. I didn't have the heart to tell the giver that there was likely very little of that original South Dakota yeast in that starter anymore! There is a nice discussion about this over at http://chowhound.chow.com/topics/707973, which refers back in places to this excellent website. In fact, I gather that the yeast that is responsible for SF sourdough -- lactobacillus_sanfranciscensis is actually native all over the world.
From recent reading (and I unfortunately can't recall the source) research into sourdoughs has shown that getting a sourdough culture started in sterilized flour (irradiated) with only air exposure is very difficult. It can happen, but is rather rare. This strongly suggests that the bacteria and yeast that become established in the sourdough starter are endemic to the flour/original grain. This might also explain why people who try to create sourdoughs using bleached flour often seem to have problems as one would anticipate that bleaching would reduce the microflora population.
Good point about bleached flour. That makes a lot of sense that such flours would contain little viable yeast (or bacteria). That also is consistent with the idea that freshly ground flour makes for a better native rise, since wheat berries are almost certainly unbleached. While I've been working mainly with bleached bread flour for my sourdough, I should add some of my freshly ground whole wheat to give it a natural yeast kick. By the same token, I suppose one could say that native sourdough made exclusively with bleached flour is likely to be dominated by local strains.