The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Science question - localized bacteria and impact on crust formation

bnom's picture

Science question - localized bacteria and impact on crust formation

As you know, David Snyder and others on this site have been trying to replicate the distinctive flavor and character of San Francisco sourdough. For me, a significant part of the SF SD flavor and experience is a thick, crunchy, deeply carmelized crust (for me, the Laraburu Brothers bread I grew up on was the epitomy of SF SD).  I recently made David's fourth iteration of the SF SD bread formula he's been developing and found the flavors exceptional but it did not have the crust qualities that I think are typical of SF SD.  

Now, after reading the following excerpt from Reinhart's Bread Baker's Apprentice I'm wondering if those of us not living in SF can achieve that same crust quality.  Reinhart writes: "San Francisco sourdough bread, for example, has a particular type of local bacteria call Lactobacillus sanfrancisco that gives this bread a different quality, more sour with a thicker crust, than any other wild yeast bread made in other parts of the world."

I'd be very interested in hearing from those with insights into the science of wild yeast and bacterial organisms.  Does Reinhart's comment ring true?  Is it possible to replicate an SF SD in the absence of lactobacillus sanfrancisco? 



LindyD's picture

Once scientists knew what to look for, they started finding L. sanfranciscensis in starter doughs in other countries—in French levains and German Sauerteigs,for instance, and in the dough for Italian panettone. Wherever it shows up, says Michael Gänzle, a microbiologist at the Technical University of Munich in Germany, it probably comes from bakers' hands. 

At least according to this article:


Mini Oven's picture
Mini Oven
bnom's picture

Did you understand any of that?  

Mini Oven's picture
Mini Oven

lacto-beasties (btw there are more) plus the variety of other lacto-beasties in the culture, no two samples being the same... means that sourdough cultures can vary.  The study did not tell us that all the bread from these different sourdough cultures tasted the same or that they varied greatly in taste.  It did say they all contained L. sanfranciscensis strains.   It does speculate that the handling (this can include all variables) of the cultures can make a difference in the bacterial profile.    I quote the paper I linked:

"This study demonstrated that ribotyping was useful for distinguishing L. sanfranciscensis strains. A further important result is that the intra-species diversity of L. sanfranciscensis strains seems to be related to the sourdough preparation."

My own thoughts: It is also possible that even if we all start out with the same culture sample, the same flour and water, the individual differences in the way we each handle our starters, feeding amounts, time between feeds, hydration, temps, chilling, our own individual. bacterial profiles, we can individually change the bacteria profile of the starters favoring different strains of bacteria and thus alter the flavor of the sourdough culture.

I suppose it is also possible that the famous SF sourdough culture profile has also changed somewhat over the years.  Unless samples are compared from previous times to those presently being used, we can assume some changes, albeit minor to the profile, have taken place.  I don't believe that a culture could be that stable with all the different possible influences and remain the same, exactly the same, over long periods of time.  

Mini Oven

bnom's picture

Thanks Mini - I appreciate your interpreting that article for me. It would be interesting to give various bakers the same starter, flour, and formula and see how their breads compare and flavors evolve over time. 

I had always assumed crust formation was the result of flour type, hydration, steaming, shaping, etc., but it never occurred to me that bacteria contributed to the thickness of the crust.

Mini Oven's picture
Mini Oven

Why wouldn't alcohol production from bacteria and yeast lead to a different crust in bread?  I admit there might be ways to manipulate each formula to come out the the same crust results, it just might be a little different with each sourdough location.  Like changes in flour type, hydration, steaming, shaping, etc.  We all tweak a little to get what we desire and location change can mean a different tweak than before.  That is why location is so important in looking for solutions to some problems.  

I also didn't take the bacteria make-up in my starter for those changes but why not?  Always a variable and would help explain why one tweak works differently in someone elses kitchen.  

Wild-Yeast's picture

Crust formation concerns complex Maillard reactions whereas the crumb and taste have as their contributors the lacto bacters and wild yeast flavonoids. Which contributes what is another bag of worms.

On reflection, it's a much better question than I first realized. May even have to do with how the bread is entered into the mouth and masticated spreading taste across the palette. Thought provoking...,

BR Wild-Yeast

bnom's picture

Reinhart states that the bacteria contributes to crust formation (implying that the contribution is sufficient to make SF SD crust distinctive from others).  And your comment about how the bread is masticated and how that affects flavor is indeed thought-provoking.  I'm intrigued by this whole issue because I have such a strong memory of the flavor of the Laraburu SD I grew up on and I'm quite sure it was the crust, more so than the crumb, that gave that bread such a distinctive flavor profile (distinctive from other SF SDs). 

Wild-Yeast's picture

I remember the bakeries in North Beach all used Sel de Mer sea salt for baking sourdough bread. I believe this was near universal with all sourdough bakeries in San Francisco including Larabaru Bros. and may be another key ingredient factor in the pursuit of SF SD bread.


Wild-Yeast's picture

Another piece of the evidence trail. 

The gas fired brick ovens that baked sourdough french bread in San Francisico bakeries were all gas fired with an iron steam tray that water was admitted to by a piping valve outside the oven once the bread was loaded and the door closed. These ovens cooked bread differently than conventional home electric/gas and even wood fired ovens. The strangely odd combination of a beginning low temperature steam blanket combined with direct radiant heat had a distincly positive effect on the crust....,


Mike Avery's picture
Mike Avery

These are some tough questions...

It is worth starting out considering that when the San Francisco Chronicle wanted to find the best San Francisco Sourdough bread in San Francisco, La Brea won.  It was a double-blind test, but the editors KNEW that couldn't be right.  After all, La Brea is made in Los Angeles!  So, they repeated the test.  And La Brea won again.  So, on question one, you can make a San Francisco style sourdough bread in other places.  Some of the keys are flour and technique.  Most of the recipes on line, including mine, are fundamentally flawed.  Look for Sugihara's papers.

On the topic of sourdough cultures, the question is far from clear.  Let's start with a simple notion.  People have been baking sourdough breads that we would recognize as such for somewhere between 6,500 and 10,000 years depending on which food anthropologists you believe.  Most of the bakers weren't literate, and for most of that time NO ONE had any notion of what yeast or bacteria were.  Still, they made good bread.  So, we can ask, "is knowing this really necessary to baking good bread?"  Of course, the good bakers taught apprentices what worked, and the apprentices repeated it, slowly refining it.  You can do that without understanding what's going on.  How many of us could build our own integrated circuits and then our own computer?  Still, we manage to use our computers pretty well.  (I could make the same point using cars as an example.... how many of us could make something as relatively unsophisticated as a Model T?  Still, we can drive to the grocery store pretty well.)

But, what is happening in a sourdough culture?  LOTS!   If we look at natural sourdough starters, the ones we make ourselves using flour and water, there are a lot of misconceptions.

First, the critters are on the flour.  If you mix your flour with boiling water to sterilize it, you'll typically fail to get a culture started in excess of 90% of the time.  Use whole wheat flour and water and you succeed over 90% of the time.  So, yeah, there ARE critters in the air.  But not as many as you'd think.  Most starters are started by the critters in the flour.

Next, there isn't one yeast and bacteria on your flour, or in your starter.  There are many.  Many are killed off as a starter becomes mature - the leucononstoc bacteria can't stand the acidity produed by lactic acid bacteria and die off.  However, there are a number of yeasts and bacteria on the flour that can form a stable starter.  Which ones win in the miniature Darwinian extercise we call "starting a starter" depends, in part, on the temperature of your starter and how you feed it.  More frequent feedings favor some critters, less frequent favor others.  You can make good bread with any of them.   Which critters you have to start with depends on your flour.  So, look at the bakery whose bread you want to emulate and see where they get their flour, and what kind it is.  Get the same stuff if you can.

We like to think that our starter has one yeast and one bacteria in it.  And... that's not quite true.   In most mature starters one yeast and one bacteria are dominant by orders of magnitude.  But, that doesn't mean they're the only fish in the pond.  The others are there.  If you change how you handle your starter, you can change what critters are dominant.  So, you move from San Francisco which tends to be cool, to Dallas, Texas which tends to be hot.  Even wth air conditioning, Dallas tends to be hotter.  So, your starter will change.  If you decide twice a day feedings are too much hassle, so you go to daily feedings, you have altered the environment.

Some changes are quickly apparent, some take longer to manifest.  If you usually feed your starter an all-purpose wheat flour and switch to whole-wheat a lot changes all at once.  You are using a flour with a lot more mineral content.  And the change in food can change the taste and aroma of an organisms by-products.  (Many nursing mothers can tell you their babies become fussy after mom eats this or that.  Feral hogs that have been eating acorns are prized by hunters.  And how French farmers feed their geese to make Fois Gras is well known.)

So, you switch the starter to whole wheat.  And almost at once, it becomes more pungent. 

Over time it changes more.

How much is due to the change in the food, how much is due to a change in the critters in the starter?  Do different critters from the whole wheat take over the starter? Is there a fresh mini-Darwinian battle for the starter going on?  I suspect that on this side of a micro-biologists lab, we won't know.

More to the point, while it is interesting to know (and I read a lot of scientific papers), it really doesn't help us make better bread.  We can only make bread with the flour we have, and with the cultures it will support.  My thought is most bakers would be better off getting a starter, learning how to use it, and to work on their bread making skills.  If you can find a master baker to apprentice under, that might be the best approach.  Find one who makes bread you like.



rossnroller's picture

I reckon the craft of baking artisan SD bread is somewhat analogous to creative writing (OK, we're comparing an art with a craft, but there is lots of bleedover there, too).  That is, there are uni libraries full of literary theory and criticism of works of literature, read mostly by other academics and hapless students labouring through lit courses, but very little of this esoteric stuff is contributed by fiction writers, who generally pay little heed to such material.

Are uni lit courses a pre-requisite for great fiction writing? In many cases, certainly not. In some cases, a literary education surely helps. Reading other works of fiction is far more important, though. And any writer will tell you that the only way to learn to write is to write - a lot!

Pretty much the same for artisan bread baking, I'd contend. Of course, you've got to acquire some knowledge, whether through a mentor, or via books and sites such as TFL. But do you need to know the science at a micro level? Well, I know you don't!  That is not to say that some folk won't find it useful and interesting, though.


Mike Avery's picture
Mike Avery

I'd actually argue many college level writing classes are counter productive.   If you look at either the best seller lists or at the books that are appreciated by the literati, I think you'd find that few of the authors were the product of a college English department or creative writing classes.

Similarly, most of the scientific papers I read about baking and sourdough are actually relevant to a real-world baker.  I keep reading them becaue I find some of them interesting.  But fewer are actually useful.  For example, it is interesting to know that there are a number of native species of sourdough yeast and bacteria that are largely unique to different cereal crops.  Barley, wheat, rice, sorgum, tapioca, and others all have a largely non-overlapping set of critters.  Any of them can be used to start a sourdough culture.

However, the next question, would these be the optimum cultures for using that grain to make a sourdough bread reamains unanswered.


rossnroller's picture

Don't wanna tie up the thread on this CW analogy, but briefly, no argument from me on your argument re tertiary lit and CW courses being counterproductive for writers in many cases. I was holding back in my post in the interests of diplomacy!

Re critical theory vs the creative process, I'm reminded of a student in one of my uni CW classes who, after having one of his short stories workshopped by the group, was asked what the story was "actually about." He replied mournfully in his Irish accent: "Oi don't know - oi'm only t' wroiter."

And even better. A writer named Tim Winton, who suffered through the same uni lit/CW course as I,  is now acclaimed as one of the great contemporary Australian novelists. He published his first novel while studying for his Lit degree, and won a national young writers' prize for his effort. The professor in charge of the Lit course refused to award him a BA (Lit) when he failed to satisfy some course requirement - not completing a unit or whatever. You can understand the prof being bound by regulations, but his reason for not awarding Winton a degree is ironic in retrospect. The good prof claimed that Winton "did not know enough about literature."

No more sidetracking from me. Just thought those two tales too good not to share.


Wild-Yeast's picture

Something is Wrong

Interesting that I had some real problems over the last few months with my starter's behaviour. I called Central Milling in Logan, Idaho [flour supplier] to see if there'd been any major changes to their organic flour production - there had not.  

I called around to some baker friends in San Francisco City proper and found out that they too had similar unexplained problems with their production during this same time period. They also had no clue to what was causing it.

One wag friend said it was a change in the health of whale snot being sprayed into the air off the coast by migrating whales - for some reason that made me think of water and that's when the light bulb went off - It's the water stupid!

Hetch Hetchy Connection

The San Francisco Municipal Water Department has been engaged in a decade long earthquake improvement of the Hetch Hetchy Aqueduct that brings water from the Hetch Hetchy Valley reservoir to San Francisco and environs. I get my water from Hetch Hetchy - a major consideration for where I bought a home.

Hetch Hetchy water is among the most pure, if not the purest, water supply in the World. The Hetch Hetchy Valley is a near double of the Yosemite Valley - a granite lined glacial valley that leaches very few minerals into the the pristine snow melt from the Sierra Nevada that fills the reservoir every Spring.

Yes, you don't have to buy bottled water when you come to San Francisco! The water out of the tap tastes like water straight out of a Sierra stream.

Ok, enough of the sales job but I'm waxing on the water quality because it is that good - until recently.

Earthquake Work

Work on making the aqueduct more resistant to earthquake damage during a major event resulted in alternate water sources being "sourced in" during the last 9 months or so. I also hadn't noticed that the water quality reports emailed on a regular basis had ended - a victim of the ongoing recession.

Sometimes things have a rough journey from the eyeball's experience to the cerebral cortex's internalizing what it might mean. I can attest that this was one of those moments on my part.

When a water district switches water sources they have a tendency to load the system with chlor-amines and loads of aeration. This is readily visible everytime you flush the toilet. I was acutely aware of this but alas, failed to cross the abyss as regards it's effect on the sourdough.

I can only thank my lucky stars that I had a great amount of healthy starter able to adjust to the sudden water quality change. Trying to navigate through this episode with a newby starter could have resulted in real disappointment. 

Happily Hetch Hetchy is back online and so's my sourdough production.

Long Story - the Point?

The point of this story is that sourdough is greatly affected by water and its quality over the long term. Upset the water quality and all bets are off, you'll be left wondering whatever happened to your former happy life before the water changed.

San Francisco has not always been blessed with one of the World's greatest water sources but since Hetch Hetchy's inception the legend of San Francisco Sourdough has become famous around the World.

A coincidence? Not in my book...,



azelia's picture

After reading so many comments about bread/starters and so much of it is off the mark and pointless because of what they leave out, finally nice to read your comment Mike, yes flour!

Why does no one ever talk about flour?  They obsess about whether it's 65% or 67% hydration or steps in the formula but the ingredient that matters not only to a starter but to the loaf one ever mentions flour. 

Maybe it's the way the flour is sold to us, ready-mix from the mills, made up of different varieties of wheat to achieve the "right" performance for the baker, the miller becomes the Blender, and all the baker needs to do in effect is Bake-by-Numbers.  It's not until you start to see the milling side do you start seeing a whole part of the baking process most of us bakers take for granted.

Why does it matter if we take flour for granted?

It matters on different counts. Flour is not a dead material, where the only importance should be the added baker's yeast, or the levain and ingredients.  Flour is bread.

Millers want to sell their flour to the bakers and the baker's requirements become important.  The miller has a business to run and is eager to repeat business, its important to produce flour that will "perform" whichever month of the year, and year after year.  That blend of flour has to perform to the standard the baker or his machines have become accustome to.  The trouble with this process is that the miller makes all the decisions for you.  A baker can handover the making of bread to fairly unskilled hands (or those not interested) and so long as you follow certain rules, ie right amount of water, resting time etc, that flour will perform. 

Everyone is happy, so what's the problem?

To my mind it essentially means the baker loses his/her real skills, they're making Bread-by-Numbers, nothing wrong with that fundatmentally I suppose, but it hardly pushes me to my skill limit, after learning my formula where next?  Well, there's always adding trendy ingredients like squid ink or miso, or finding that obsecure formula from somewhere deep in the mountains of SouthWest France very few people know about where some old village baker is doing...I guess.

And there's nothing wrong with the above by the way, I shall be making black squid ink rolls soon...I hasten to add. 

They're all interesting things, but they are not challenging to my skills as a baker.  What does challenge me is finding interesting flour, one that isn't ready-mix for performance sake, but is made for flavour above everything else.  Another interesting area of flour is where grains are grown best to that climate it has become accustom to, which can be better for its environment but not necessarily the easiest of flours to work with. 

Receiving through the door a new interesting flour gets my baker's brain working, finding a method/formula best suited to it, seeing the changes in it since last year's harvest if any, and producing the tastiest loaf out of that process.  By the way, that flour has to produce a good loaf, crumb, crust, flavour, otherwise what's the point?  I don't live 300 years ago where bread was there for filling a hole of hunger, depositing itself like a brick in my stomach.

Flour matters as Mike says for feeding your starters and how they'll correspond. Flour also matters in the dough and the end result of your loaf.

I don't want to seem to be criticising the use of standards flour, I use some.  I have a standard organic wheat in which 6 or 8 varieties of wheat have gone into the mix, this miller makes sure this flour will perform, always.  I can make any fancy dough out of it, with fancy shapes/slashes and give it taste with my sourdough starter, but it isn't the flour that keeps my baker hands sharp.

I wanted to bring up the conversation to the importance of flour and try to give the subject some thought, that is all.


PS - Why do bakers obsess so much about hydration when flours differ in their absorption rate?


HeidiH's picture

To me, the flour makes a tremendous difference in how the dough behaves and the final taste.   Since hubby and I love variety, I have several bags of different flours (most from Stan at open at any one given time.  When it's time to make a loaf of bread, I stand in front of the flours and contemplate what I want to have.  Each flour and combination of flours makes different bread.  I've decided that for grocery store flours, I prefer the taste of GM to KA, which is a bonus because GM is a little cheaper.  We are "moving to the big time" here in Columbia and will soon have both Trader Joe's and what hubby calls "Whole Paycheck."  I hope these offer some new flours to try.


Wild-Yeast's picture

Maybe there is a bit of magic left in this story after all. 

Some call it a fairey tale fabricated to celebrate San Francisco Sourdough French Bread while still others study it and provide irrefutable evidence that it's nothing but a fabrication - then there are those who come to San Francisco and find, to their amazement and utter enjoyment, that there really is something to the fabled taste of the bread made naturally there.

Fact of fiction"? You'll just have to come and taste the real McCoy and decide for yourself...,

And so the story rolls on...,

sournewb71's picture

You know...

I started this hobby with a couple cultures from Ed Wood and his book.  I was keeping my starters in the refrigerator feeding them once a week or so.  At the time I wasn't sure if there was a point of keeping two starters because it seemed they were the same.

Fast forward a few months later...I'm feeding both starters daily and leaving them on the counter.  While I haven't done a side by side loaf sample, both starters now have a distinct and different smell to them.  How is this possible?  I maintain them both with the same whole wheat flour, the same filtered zerowater, same feeding ratio and the same feeding times.  The only answer is there must be some kind of dominant strain of bacteria or yeast or both that came from the original starter that has kept perpetuating.  Time will tell.

Wild-Yeast's picture

My most recent batch of sourdough turned out to have that magic Larraburu crust, crumb, mouth feel and taste. It's the result of a lot of tinkering with the same basic formula. The only remaining issue is that the oven spring is not nearly a great as I'd like but if that's the tradeoff then that's acceptable.

I plan to run this build experiment for two more runs to insure that it is not an oulier.  This time I'll record all the details so that they can be shared.

Short Synopsis:

  • Larger upfront sourdough biga percentage
  • Use of a whip to mix biga with water and flour [a portion of]  into a smooth, arerated batter
  • Warmer rising temperature
  • Extended hydration rest
  • Dissolved sea salt in water
  • Increased stretch fold & sheath development
  • Extended proofing times
  • Extended prebake warm-up following retard


bnom's picture

I  eagerly await hearing the details  and seeing photos of your efforts!