The sources of sour
I have recently been running a series of experiments to tease out the relative significance of various factors that contribute to the sourness of sourdough bread.
In the "everybody knows" category is the notion that whole grain breads can be more sour than a 100% white flour formulas, but the relative importance of specific mechanisms by which the sourness is developed is not well documented.
There is a limit to how much acid you can develop in a 100% white flour starter irrespective of how long you let it run before use. This limit is determined by the LAB population and their acid production rate. I have found no references that either differentiate between (or correlate) population growth rate (inverse of doubling time) and acid production rate. While the chemistry of acid production is common to reproduction, it is not clear that the LAB stop producing acid when they stop reproducing. The fact that growth stops at a pH of around 3.8 while there is ample evidence that additional acid is produced down to a pH of below 3.6 feeds a suspicion that at some point there is a decoupling of reproduction from metabolism and the concomitant acid production.
I set as an objective the development of a sourdough loaf that appears visually to be all white flour yet has a reliably reproducible high acidity.
Hamelman has a number of variations on sourdough with some amount of whole grain flour in each. In some, his levain is made from 100% white flour and in others some fraction of the whole grain flour is incorporated into the levain with the remainder incorporated into the final dough. As part of this exercise I began to wonder if there would be value in putting all of the whole grain flour into the levain in an attempt to drive up the LAB population in the final levain (i.e., do not focus on the acid contribution of the levain, but rather focus on how many LAB get added to the final dough). The thought was that a higher numerical density of LAB in the final dough could produce more acid during bulk fermentation and proofing (when the pH is well above 3.8) than they could produce under the limiting conditions of the levain build (relatively small quantity and the development of a low pH well before maturation of the levain). If by adding all of the whole grain flour to the levain could hold the pH up long enough for the LAB to double one more time before they stopped reproducing (relative to an all white levain) then the final dough would have potentially twice as much acid (subject to the other resource and rate limiting conditions of the bulk fermentation and proof).
The results seem to confirm the conjecture but also raise another issue. While including 15% of the total flour as white whole wheat and putting it in the levain makes the bread indistinguishable from an all white loaf in color, it does add acidity to the flavor profile. Yet a much more noticable difference in flavor emerges when this bread is retarded. My speculation is that the relative metabolic rate advantage of the LAB compared to the yeast during retardation (either at 50°F or 42°F) is the source of the additional acid. Some samples of this formulation have produced crumb pH below 4.0 and TTA values of above 12 (ml of 0.1N NaOH to titrate 15g of macerated crumb in 100 ml of distilled water to a final pH of 6.6). Without any whole grain flour or retardation the TTA is 8.70 to 8.85, while with the substitution of 15% of the flour with white whole wheat the TTA climbs to ~9.5 for no retard and to above 11.0 when the dough is retarded in excess of 6 hrs. The sample size for these tests is not yet large enough to determine the significance of the difference, and there are other factors that are not yet firmly under control (e.g., the time/temperature profile for levain growth), but the direction of future tests seems clear.
The next step is to more tightly control the levain, increase the sample size, and add another test case where the whole grain flour is added to the final dough mix and none is included in the levain (with and without retardation).
Since the test matrix is getting too large to explore completely, I will have to make a decision about what cases to emphasize and which cases to defer.
I would be interested in comments from anybody who has managed to read this far without falling asleep about which cases seem most interesting or worth the trouble and any insights as to why some cases might be eliminated.
is a key point for sour but restricting the yeast population to extend ferment and proof times is just as important. The more time the LAB have because the yeast are restricted the more sour will result.
I also agree that using whole grains in the starter and levain will make for more LAB and sour too. Even better is to grind fresh whole grains, sift out the 20% extracted hard bits and feed that to the starter and levain instead of the whole grain itself.
The best way to restrict the yeast is to use temperature. 36 F cold retard for a very long time for starter storage and and using 92-94 F for ferment and final proofing. If you increase the LAB population in the starter and levain and then restrict the yeast population while building both at higher temperatures when out of the fridge where LAB are on steroids but the yeast are reproducing like it is 60 F you can inoculate your dough with much higher LAB counts and then use 93 F to really give them an additional advantage for ferment and proofing. IF you make a white bread t=hat ends up with another 15% whole grain int eh dough flour you can really get get some outstandingly sour bread.
Here in AZ we get 93 F without a proofer in the summer so getting More Lab than yeast is pretty easy :-).
@dabrownman
For a batch that will contain 15% whole grain flour, I should combine all of the whole grain flour plus 15% white flour to get up to the 30% of prefermented flour that I want, and all of the water with enough starter to make the timing work out, and ferment it at 32°C until it reaches pH 3.8 and the LAB stop replicating which maximizes the ratio of LAB to yeast. Then add the white flour and salt, mix, bulk ferment, divide, shape and proof at 32°C. Beginning with a refrigerated starter that has a high ratio of LAB to yeast will further enhance the LAB/yeast ratio.
Tell us why it is so important to "restrict the yeast population", according to you.
ratio from the standard 100-1 to something higher so that there are more LAB making acid than normal resulting in a more sour bread, He though by using whole grains instead of white flour would help increase the LAB population and I certainly agree with that. In fact, I routinely sift out all the white parts of the home milled flour and use the hard bits to feed the levain to promote LAB over yeast as best I can with food, The other way to do this is to increase the hydration. LAB love the wet a bit more than the yeast do so they will reproduce a bit faster in higher hydrations - more LAB means more sour.
Increasing the LAB population is one way to get more sour but an even better one in my book is to restrict the yeast.population. Less yeast means it takes the dough longer to ferment and proof and the more time the LAB have ti make acid the more sour the bread will be. The way to do this with with temperature. LAB always outproduce yeast, if there is enough food, at all temperature ranges from 36 F to 94 F But at very low and very high temperatures the LAB really have an advantage.
The problem with low temperatures is that both LAB and yeast almost shut down reproduction entirely and it takes a very long time to increase LAB population over yeast in the starter. LAB are outproducing yeast 3 to 1 but at 36 F this advantage is minimal unless you retard for a very, very long time - which is why the No Muss No Fuss Starter technique I developed is 8-16 weeks cold before it really starts to make a more noticeably sour bread..
The real way to restrict yeast populations and increase ferment and proofing times while allowing the LAB population to explode is to do all the bench work of gluten development as well as ferment and proofing at 92-94 F. The best temperature for year reproduction is 84 F, and at that temperature, LAB are outproducing yeast by 30% or so even though yeast are reproducing at their max rate. AT 75 F LAB are outproducing yeast by only 2.4%. But at 93 F LAB are outproducing yeast 13 to 1.and yeast reproduction rates are about what they are at 55 F - quite a restriction..
So to really kick sour into gear the fastest easiest way to do so is to ferment and proof at 92-93 F where yeast are severely restricted and LAB are on steroids. There are two problems. Once the acid level gets too high the LAB reproduction shuts down and if the mix runs out of food things slow down dramatically even though LAB have no problem eating dead yeast
So the best way to increase sour is to makes sure the mix has enough food and use temperatures below 46 F and over 84 F to restrict yeast populations while promoting LAB. It's the high LAB to yeast reproduction ratios that make for sour bread and those happen at those temperatures. Here is a temperature chart that shows LAB to yeast ratios in a SD culture..
The general rules for sour bread are
Use whole grains
Use higher hydration for levain and dough
Use low hydration and long cold retard for starter - 8-16 weeks (Low hydration helps to make sure it has enough food)
Use temperatures lower than 46 F and higher than 82 F for gluten development ferment and proofing ( preferably the higher temperatures instead of the lower ones)
Happy Sour Baking
I have recently come to appreciate that while Ganzle did great work and derived a simple, low order model that fit his lab data quite well, his model was not based on first principles, it was based on empirical data. Thus we should not expect high accuracy at the edges of the band or outside the zone where the data was collected. I have no doubt that there is some temperature at which the relative growth rate is 13.127 but the specific temperature may not be exactly at 34°C in our dough (though it is probably close). On the low end, my experience is that LAB continue to metabolize below the range over which Ganzle's model is valid. This is not an indication that the model is bad, just that one should not use the model in place of experimental data when more precision is needed than the model was intended to deliver.
at the extremes the accuracy is suspect. We know that yeast can be proved at 105 F no problem by putting some sugar in water with the ADY and according to the scale it should be dead:-) But, like you say it is probably good enough for any home baker to use as a guide.
Happy baking
I am pretty confident that Gänzle got the upper temperature limit for the yeast he was dealing with correct, and while it may not die at temperatures mildly above 105°F, it was most likely not actively reproducing. ADY is definitely a different breed which fares quite well at pretty high temperatures (and I don't know how high it can go but I have seen recommendations to rehydrate it with 125°F water).
What I hear is a suggestion to shift the "normal" ratio of LAB to yeast from 100:1 to some higher value by running the propagation process at a temperature where the yeast won't replicate but the LAB will. And your guidance is that below 36°F the yeast are inactive while the LAB continue to grow. Then when you bulk ferment and proof, go to the high end of the thermal tolerance band where the LAB retain a huge growth rate advantage over the yeast.
I like it. And suppressing the yeast to allow the LAB time to do their thing is an approach that I had not considered. My first thought is that this sounds similar to the Larraburu process, and my next is to wonder what the new LAB:yeast population density is and to question its stability.
I have not checked the pH of my proofed dough so I don't know how close it gets to shutting down LAB replication, but with baked crumb pH of around 4.0 or a little lower I am on the low side of "industry normal" numbers based on the following information.
The source for the following quote was http://www.nyx.net/~dgreenw/howdoesonemeasurethephofso.html indicating that:
Anything above 3.8 is high enough that the LAB are still replicating and certainly still producing acid so extending the proof should further increase the acidity. And since the LAB are not generally limited by the supply of nutrients, that should not slow them down.
I will have to go back and model the impact of reduced yeast population on timing of the bulk fermentation and proof. While the low pH will bring the proteases out, the high temperature will drive up their activity, so there should be a big payoff from using a high gluten flour and lower hydration.
Still looking for information on LAB acid production at pH<3.8 where replication is inhibited. I suppose I can run some TTA measurements on sequential samples from a batch of propagating starter and plot pH vs time and TTA vs time. It is a lot of work but it might produce some interesting data.
Thanks for the insights and stimulating thoughts.
and complicated to adequately model. I've been doing a fair amount of online literature research on both the yeast and LAB components. Perhaps the best current summary is the rather expensive 'Handbook of Sourdough Biotechnology' published by Springer. If you do a Google search on biochemistry of sourdough you can pull up a fair number of public access papers that will help you out in this regard.
I'm pretty sure I commented on a previous thread that you or someone else started on this topic. Anyway, here are some observations. Sourness is taste dependent and each person is likely to respond differently. We know that the three principal acids that contribute to this in sourdough bread are lactic, propionic and acetic. All three have very close pKa values and will equally contribute to the final pH of your dough irrespective of their final concentrations. I don't know how each contributes to 'sourness' and whether the taste receptors are equally responsive. I guess my point here is that 'sourness' may not be much different whether the pH is 3.9 or 4.5. Until there is correlative data between pH, concentrations of the various acid components, and individual taste response it is difficult to draw any firm conclusion.
You state "And since the LAB are not generally limited by the supply of nutrients, that should not slow them down." I find this a surprising statement as it controverts basic microbiology. If there are limited nutrients, both growth and intermediary metabolism are necessarily limited.
Finally, and most critically, a balance needs to be struck between the yeast and LAB. If you restrict yeast growth and metabolism you sacrifice oven spring. Similarly, if you adopt conditions unfavorable to LAB you get nice looking bread with little sour taste.
Sourness is not related to acidity - for example, lactic acid has lower pKa than acetic, that is it is more acidic. However, acetic acid is significantly more sour.
everything to do with acidity. If no acid then there is no acetic tang and no lactic sour. The best tasting SD bread in my book is one that has both acids in abundance in conjunction with the flavors created by the yeast - but no acid would just be yeast bread.
Happy baking
, I meant exactly what I said, there is no relation between acidity, pH or TTA (which are also not explicitly related to each other), and sour taste.
zero sour taste....so there is a relationship between acid and sour taste. Just taste a yeast bread where there is no acid and viola - no sour taste and taste a SD one where there is acid and the sour magically appears :-)
moved down the page... sorry :)
With more LAB than yeast you get a more sour bread. Restricting yeast just means the amount of time it takes for the bread to proof just takes longer than normal it still proofs to the same level or % with spring being the same. But, since it takes longer for the yeast to raise the dough to the proper level the LAB have more time to produce sour.
All you need to to remember is that you don't want the LAB or Yeast, in general terms they kike different sugars, to run out of food and you don't want to get too much acid but they do work together to each others benefit.
Suave's comment about what micobs you have in your SD culture are unknown and may perform differently than the SF LAB and yeast in Ganzel's experiments . But since we have no data on our own cultures the best we can do use use the data we have and hope it is similar. in my case, I know that what Ganzel's experiments point too also work for mine.
Happy baking
That's not necessarily always the case. You need to understand that the reason Lb. Sf. is investigated so much is not because it is a primary or most important sourdough LAB, it's because it is the only system that lends itself to scientific study - one species of LAB, and one species of yeast complementing each other while relying on different energy sources. There's simply nothing else quite like that.
I'm not sure how many exactly there are now but at least a dozen each of LAB and yeast have been found in SD cultures. Come are combinations of each We also know that each combination what ever it is live together in an acid environment eating sugars to produce, acid, co2 and ethanol. Each one acts a bit differently for sure but as a group they do much the same things overall and in a symbiotic way without eating each to dominate the culture alone - LAB or yeast.
I find the the idea that lb SF and its yeast are unique in relying on different energy sources in SD cultures to be pretty much a myth. We know for sure that while one may prefer say maltose the other can matabolize it too if its preferred sugar is gone. LAB can produce co2 and ethamol too just like yeast - but yeast won't be making acid any time soon.
At best, i suppose one could say that the LAB abd yeasts found in SD cultures share energy resources to make acids, co2 and ethanol without killing each other - but LAB will eat dead yeast no problem :-)
You are confusing acidity and sourness. To make the taste more sour you need no so much to increase the <relative> amount of LAB, as to shift fermentation towards producing more acetic acid which is the primary ingredient responsible for the sour taste. Your ability to do so will depend to a large degree on the species that populate your starter.
Most of the acid is lactic and acetic with small amounts of tertiary species. Acetic acid is volatile, some is lost in baking, and contributes strongly to the smell of the bread while lactic acid is the dominant component of what you taste.
Lactic acid is indeed a considerable component of the taste, except that its main contribution is not sourness. What people call sourness is actually two separate feelings, sourness proper, and astringency. Astringency is tied to pH/ acidity and is about similar for both - higher for lactic acid, but the same order of magnitude. Sourness of acetic acid is, however, higher than that of lactic acid. You can easily check it yourself.
sourdough bread in my opinion has the flavors supplied by the yeast working a long time on the dough with plenty of both the lactic acid 'tang' and the acetic acid 'sour'..As luck would have it, a 3 stage starter and levain build that varies hydration, temperature and time bring out all 3 very well. Not having one of them makes for an inferior tasting SD bread. having a dough with less yeast and more LAB in it makes the taste, much better than one with a more balanced yeast and LAB ratio. But to each their own when it comes to taste and we all like something different. i like my bread more sour and most others do not. More than 1 kind of levain in the dough is nice too - even more complex flavors from each of them,
Happy baking
I don't understand the importance of trying to manipulate the ratio of yeast to LAB.
Or simply increase the proofing time.
We all know about the "symbiotic relationship" between yeast and LAB, so "restricting" yeast accomplishes what from a microbiological standpoint?
Looking at the Larraburu process, a proofing temperature of 41 C slows both yeast and LAB reproduction way, way down. One of the first questions to ask is why the "other" sourdough bakery(s) didn't adopt this temperature and instead used a proofing temperature of 30 C. I don't put a lot of credence in the description of the Larraburu process.
are more yeast, More yest means less proofing time at every temperature, It is an easy concept to grasp but harder to do in reality. By having a starter, levain and dough with less yeast and more LAB in it means; more time to ferment and proof for it to be ready to bake along with the resulting ,more acid and sour because the more LAB have more time to do their thing.
I don't know where you found the Larraburu process was done at 41 C? It was a closely held secret as was their starter itself. This is way too high a temperature for a type 1 sourdough and way too low for a type 2.. It was rumored that Larraburu used higher temperatures than the other SF bakeries, more likely around 82-33 C. Their bread was more sour and considered the best sourdough bread in the city by many and that was the one people brought back from SF since it was sold at the airport. - the gold standard really but favorites of the locals depended on where you lived too, i liked Columbo better but that was close to where I lived - which has more to do what people liked it seemed.
I think it telling that people will post every so often on TFl that their bread isn't sour or lost it's sour. Every time it seems to turn out they have a white starter maintained on the counter at room temperatures between 68 and 74 F and make their levain with white flour and bread at those temperatures. Once i tell them to get some whole grains in their starter and levain and raise their temperatures - magically the sour comes back :-)
You might also look at the Detmolder process to see how: hydration, temperature, time and grains can be manipulated to bring out yeast, acetic acid and lactic acid over a 3 stage build.
http://germanfood.about.com/od/germanfoodglossary/a/Detmolder-Three-Phase-Sourdough-Method.htm
happy baking
Here for your reading pleasure is the description of the Larraburu process from the original article.
LACTIC AND VOLATILE (C2-C5) ORGANIC ACIDS OF SAN FRANCISCO SOURDOUGH FRENCH BREAD
A. M. GALAL, J. A. JOHNSON, and E. VARRIANO-MARSTON
Cereal Chemistry 55(4) 461-468
Copywrite: 1978 The American Association of Cereal Chemists
I have never doubted the accuracy of the description, though I have not succeeded in replicating it either. Post-mix dough temperature is not reported and the starter is no longer available for test nor was it characterized prior to its demise so we can only speculate (and thus we are completely free to do so). The long, warm starter growth period and the long, hot proof would seem to argue for a relatively slow yeast which would support the notion that the LAB population could be quite high and thus the acid production robust. A clear flour with a 14% protein content (which seems high) and a high ash content can perhaps be the alternative to whole grain flour. A modest dough temperature (perhaps 30°C?) and relatively large round loaves (compatible with a 45 min/420°F baking cycle) would delay the exposure of the core to the high proof temperature for quite some time thus giving a sequential opportunity for the layers to be exposed to the elevated temperature, grow and then stop yeast growth while allowing the LAB to continue before shutting down. The high humidity proof may have played a role in trapping the CO2 in the loaf.
chris123 couldn't have seen this. He was searching everywhere for the Lattaburu process. Having seen this, it now makes sense why the old style SFSD was more sour than what they make today.
80 F is near optimum for yeast reproduction rates, so that seems quite normal and at 50% hydration it would take 9-10 hours for it to ripen. So the rumor was true Larraburu did have a much higher proofing temperature and really high humidity too. But who knew it was so high.at 105 F. They must have had the largest proofing box known to man:-) 4 hours for proof at 105 F seems like a very long time indeed. i can't get more than an hour and a half at 88 F with 15% prefermented flour? In the winter when the kitchen, is 64-68 F, I can get close to 4 hours though Something seems amiss and no wonder it ca't be replicated.. 105 F isn't all that weird since that is the temperature of the water you prove ADY at.
Thanks for posting this info.
That statement makes no sense. Proofing time is however long the baker lets the sponge or dough proof.
Not true at all. The Larraburu process was studied by the USDA and is well documented.
You're contradicting yourself. If the Larraburu process was a "closely held secret" as you erroneously claim, then there would be no factual basis for your rumor.
Assuming you meant 82F - 33C, Larraburu's competitors, also studied by the USDA and well documented, proofed at 86 F or 30 C. That's higher than the 82 degrees you stated (assuming you meant 82 F).
a dough will proof to the point it is ready to be baked based on the amount of yeast in dough. More yeast - faster proof less yeast = slower proof. You can prove it to yourself
Take a pinch of instant yeast (1/32 tsp) and put it in 70 g of water and 100 g of flour. Take the same amount of water and flour and put a tsp of instant yeast in it. We will say it is fully proofed when the volume doubles in size. You will quickly prove to yourself that more yeast means faster proof.
Happy Baking
that I understood this. I merrily baked bread according to older recipes that called for larger amounts of yeast and short proofing times. They were not very tasty. Then I read Hamelman's discussion of pre-ferments and lesser amounts of yeast. Flavors are now fully developed.
Alan
Also not true. The yeast of interest in sourdough is maltase negative.
Do you have any backing for this statement?
talking about. Yeast and LAB are just like me. I prefer to eat ice cream rather than Brussels sprouts but if there isn't any ice cream and only Brussels sprouts to eat I eat Brussels sprouts. We used to tie up everything in a tight little bow saying LAB eat maltose and Yeast eat glucose and never the twain shall meet. Now we know that isnl' really the case with all LAB and yeast found ins SD cultures. :Lab eating dead yeast can be found here. they can actually eat all kinds of things
http://www.sourdoughhome.com/index.php?content=whatissourdough
There are indeed many yeasts (and probably an equal number of LAB species) that work in various sourdough cultures. There is a paper that I can't lay my hands on at the moment that examined the cultures from a large number of Italian bakeries in an attempt to find common elements. This table may have come from that paper.
around the wprld here:
https://books.google.com/books?id=il9WEQPUfk8C&pg=PA119&dq=3.5+50&hl=en#v=onepage&q=3.5%2050&f=false
It is interesting to see that Lb.sanfranciscensis was found in Germany, Italy and Greece, as well as the U.S.
It is also interesting to note that Lb.sanfranciscensis was found in both wheat bread and rye bread.
Thank you for posting the Larraburu process again, Doc.Dough.
My question remains: If it worked so well for Larraburu, why didn't the competing bakeries adopt Larraburu's hot proofing temperature? It has been documented that the competing bakeries proofed at 86 F.
It's hard to remember what something from 40 years ago tasted like exactly, and Larraburu is no longer available to do a side-by-side comparison. My own version of Larraburu is close enough for my tastes. Whether I've nailed it exactly is an open question.
In my experience (and I've done a lot of trial and error) if you want to replicate the major old-school brands of S.F. sourdough you need to stick with white flour. I've used AP and bread flour without noticing a drastic difference between the two.
I suspect that any successful bakery with an established customer base would be hesitant to attempt to copy a competitor's product/process. If they got it perfect they have to capture some fraction of the competitor's market, perhaps invest in substantial new capital equipment (at risk), and they would have to do it in parallel with continuing their already successful business. So it is a risk and a distraction for little potential advantage. Of course if the starter is well protected and the process is not perfectly clear (which it might be if they hired a senior staff member - if there were any), the perceived risk might be quite high.
A new competitor would have to have the starter and process knowledge and a source of capital. Not a likely combination.
A couple of years ago when cupcakes were all the rage, you didn't see much outright copying, and the barriers to entry were quite low relative to a full blown specialty bakery.
As a kid, when I lived in Redwood City, I lived close to the Pisano bakery so I don't think I ever had the opportunity to eat Larraburu bread and it is only in retrospect that I learned how good it supposedly was. As it is, I now remember La Brea bakery (when Nancy Silverton still owned i) and their sourdough was my model of what great sourdough should taste like. Today, I picked up a loaf of La Brea French Bread to test the crumb pH and TTA. Of course I tasted in along side some of my bread from yesterday. I was frankly disappointed. It was not as good as I remembered; the TTA was a not very exciting 3.1 (with a crumb pH of 5.08). Made with "sour culture" and yeast (which is not a derogatory statement since I can understand why a commercial bakery would use yeast for schedule reliability and might still deliver a great loaf of bread). It just wasn't that good. I will have to search for a new model of perfection.
Twice I have had the La Brea bakery sourdough (not French) demi baguette. The second time I shared it with a co-worker from Redwood City who is also quite familiar with Larraburu. We agreed the La Brea sourdough was bland and utterly lacking in flavor, not worthy of being called "sourdough".
I'm from Palo Alto but don't remember ever having Pisano. Ours was a Larraburu household until the bakery closed in 1976. My sister in law knows people who were in some way involved with the Pisano bakery.
A bakery needn't necessarily have changed its proofing temperature along with the associated risk you described. One might wonder why the higher temperature used by Larraburu wasn't the de facto standard used by other bakeries from the outset , in which case it wouldn't have been necessary to change anything.
When I look at the temperature graphs I wonder if it's worth trying a higher proofing temperature. In order to do that I would have to get my proofing apparatus to go up to the higher temperature.
Pisano was on Main St near Maple (close to Five Points where Woodside Road and El Camino and Main St come together) and eventually moved to a larger facility out closer to Bay Shore, then got bought, probably in the mid 60's. Somewhere I have some old photos that I found on-line from a Redwood City historical site that had some information in the captions.
I see Pisano opened in 1950 at Main & Chestnut, then moving to Maple St. & Veterans Blvd. Is that correct?
The Dumbarton railroad branch split off from the main line around Five Points, then crossed the bay on that turnstile bridge. There used to be a railroad tower there.
That sounds right.
That's still true. The microbiology hasn't changed. However, the way you've described the situation above is incomplete.
understanding of it and most other things in science. It is estimated that 97% of all science facts of the past have now been proven wrong by later scientists who found out they were oh so wrong before. It is just the way things are. We used to think one thing about LAB and yeast in SD and now it has changed many, many times. This is no exception. Another way to look at it is that 97% of science being done today is wrong and bad science we just don't know it yet.
Yeast is the one living organism that has been experimented on more than any other, by all kinds of scientists, and we know more about it than just about any other living thing. Still we find out new things every day and that much of what we thought we knew was wrong. So no worries - all things change - or die.
This is how all science was described to us in our freshman year biology class in college - 40 odd ears ago. It is one of the few things proven right over that time:-) My description of the situation just didn't fit your understanding of the matter. Luckily for both of us, future scientists have a 97% chance of proving both of us completely wrong.
I was sort of stunned when some recent new experiments on some SD cultures point to the fact, eeerrrr ......idea that more than half of the CO2 gas produced is made by LAB and not yeast . That sort of would put to rest the current general idea that LAB make acids and a bit of CO2 and a bit of ethanol under the right conditions while the yeast make huge amounts of CO2 and ethanol - the times they are a changing.
Happy baking
@dabrownman
I am interested in reading source material that rationalizes LAB production of that much CO2. I have been assuming that LAB are minor sources so that CO2 production could be used as a proxy for yeast population. If the 50% number is representative then I need to revise my thinking.
and will find it soon enough. The first thing I thought of is that maybe we could make SD bread without yeast at all but i'm guessing that the pH would get too low and would stop production of everything LAB. Some yeast in SD also produce twice the co2 as other ones common in SD. One thing that is on the horizon soon enough is genetically modified LAB and yeast made for SD cultures that will provide the best of all worlds in finished bread when it comes to taste, rise, browning etc. Thankfully what people like is different so a wide range of genetically modified SD cultures would have t be available,
When i find the paper i will get it off to you.
That's not what the graph says. It says the reproduction rate is very, very slow.
at 41 C (105.6 F) the graph is zero meaning - no reproduction for yeast in the study at that temperature. Even if the chart was correct at that temperature, which it probably isn't,t that doesn't mean the yeast are dead they are perfectly fine to do the other things they do besides reproducing. You can take ADY put some sugar and water in a small bowl and it will prove just fine bubbling away making CO2 gas and ethanol no worries. - even at 110 F.
Happy baking
Conjecture:
When two species are dependent on the same food source, the only way for a stable population to evolve is for the one with the higher metabolic rate to have a limiting factor other than food supply exhaustion, while the species with the lower metabolic demands can be limited by food supply but may not be limited by the same factor as the more aggressive species. This situation might be called compatible species in a stable culture.
For sourdough starters, pH is the limiting factor for the LAB and the yeast is unaffected by pH while consuming all available food to exhaustion. Neither yeast nor LAB are significantly intolerant of the principal waste products of the other.
Synergy
When multiple species consume different foods, and one or more can consume byproducts of other species metabolic activities, then there are feedback terms that affect the population dynamics other than food supply availability. While this does not require co-dependence, it does offer synergies that may ensure survival of some species while others die off under the same conditions. If the feedback terms don’t balance out, the end result is a monoculture, and evolutionary events are required to establish stable relationships.
In the case of lactobacillus sanfranciscensis, it uses maltose as a food source and while it consumes one of the two glucose units, it excretes the other one which provides additional glucose for the yeast. And I suspect that this synergy is one reason why it is found in so many sourdough cultures; it supports it cohabiting yeast with an appropriate amount of food when times are lean.
And in the case of Dabrownman's very stiff whole grain starter, the reduction of yeast population in old, refrigerated starter is perhaps a manifestation of this phenomenon of stable synergy. With the higher (relative) activity of the LAB at low temperatures, there is sufficient glucose produced as a byproduct of LAB metabolism to feed some number of yeast cells; just enough.
It's worth noting that the experiments on L sanfranciscensis were done in the laboratory and things are going to be quite different in the real dough world. IIRC there is not much maltose in normal flour so I"m not sure how applicable this might be. Glucose is the most ubiquitous food source for microoganisms so even if some is excreted via maltose metabolism there will competition for food by the various yeast and LAB. All of this is making me wish I was back in the laboratory so I could do some proper experiments. I would also like access to a good scientific library so I could go back and read the source articles without having to pay an arm and a leg for copies. I'll have to see if I have library privileges at our local state university though they don't have anyone on the faculty with interests in sourdough technology.
it is mainly starch. But this is where an autloyse of flour and water does its magic. Once water hits the mix amylase enzymes break down these starches in maltose, fructose the LAB prefer and another enzyme called maltase breaks maltose down into glucose that the yeast prefer as a by product. There is normally plenty of food for everyone without an autolyse but with long retards, ferment and proofs the food can be in short supply by the time baking actually happens. The sugars can be used up and the bread doesn't brown well as a result, The autolyse makes sure there is more than enough food but if you are making a wholegrain bread then it also softens the hard bits as well making for a better crumb.
The symbiosis come in since the yeast can break the 1-2% of glucofuctans found naturally in the flour down to fructose.. The thing about fructose is that LAB need it to make acetic acid - when none is present LAB make ethanol instead a real waste. So the yeast eat the glucose from the LAB fermentation and they bread down glucofuctans into fructose that :LAN need to make acid even though an autolyse will provide plenty of fructose if the flour is half decent.
My daughter got her degree in microbiology a couple of years ago and she wasn't much help when it came to SD anything. I thought about funding a research project at the university to take a look at my stiff. really long retarded rye sour starter to tell me what was going on but when i found out what they wanted to do it.... it wasn't cost effective.
Thank you AlanG and Doc.Dough for your informative posts.
If my recollection is correct, starch (amylum) is composed of glucose molecules which are converted to maltose when metabolized by amylase. That is why millers pay attention to wheat's falling number; it is an indicator of amylase activity. Am I remembering this correctly?
The article Doc.Dough posted was co-authored by Dr. Leo Kline, one of the two USDA researchers who studied S.F. sourdough in the 1960's. Kline was having trouble isolating L.SanFran, so he went to Dr. William Sandine of the University of Oregon. Dr. Sandine was able to isolate L.SanFran when he discovered that it requires maltose. It requires, not just prefers maltose. Dr. Sandine's involvement is a little-known fact about the USDA research into sourdough.
The recommendation to autolyze the dough before gluten development leads to the breakdown of starch. Clavell calls of autolyzing in the absence of starter while Hamelman and others include starter. I follow the latter recommendation. It just might be that by including starter in the process accelerates starch degradation and increases maltose and other small polysaccharides that will promote growth. Of course it's really difficult to do controlled experiments on such complicated systems.
Getting at the details of complex systems via experimental means is difficult, but perhaps a gedanken experiment is adequate to illuminate the first order effects. If there is enough amylase in the flour to make 5.5% maltose, which is subsequently not completely consumed by the LAB, then perhaps additional amylase from LAB or any other source is not needed (or even beneficial).
Perhaps including the starter in the autolyze is simply a time saver and a convenience for the baker since it eliminates an addition trip to the mixer.
Any ideas on how high the LAB to yeast ratio could go before it becomes a significant limitation on its own?
Could you make bread with LAB only? If they produce only half of the CO2, then perhaps not since extending the proof will presumably reach a point where the LAB activity stops on its own. There would seem to be enough maltose to support it, but dough pH would eventually get low enough to shut off LAB activity.
Does low yeast count slow things down to the point where protease activity degrades the gluten excessively before proofing is complete?
Are there other effects that make a difference?
Last night I came across some old data that illuminate part of the question of how much whole grain flour does to buffer the medium during starter propagation. You can see it here. There is clearly growth continuing beyond 6 hrs.
This is a very interesting paper for many reasons, from 1997, one of them showing the importance of fructose to acetic acid production by LAB in SD cultures. It also points out that Saccharomyces cerevisiae used almost exclusively in type 2 SD breads is maltose positive
http://comenius.susqu.edu/biol/312/lactobacillussanfranciscoakeysourdoughlacticacidbacteriumareview.pdf
Maltose positive yeast found in type 1 sourdough cultures in 30% of I in 5 SF bakeries tested in 1972 by non other than the famous team of T. F. SUGIHARA, LEO KLINE, AND M. W. MILLER
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC377202/pdf/applmicro00113-0071.pdf
The thing to remember is that there are exceptions to almost every rule. Not all yeast found in SD cultures are maltose negative and LAB can utilize other sugars besides maltose. Some people are allergic to peanuts but not all people are. With all the species and LAB found in SD cultures worldwide and cultures with multiple species of each in them, just about anything is possible
Check your facts.
Once water hits the mix amylase enzymes break down these starches
into maltose, fructose the LAB preferNice to see you back
This was well known many years before that paper was published.
That's interesting. If you're familiar with Kline and Sugihara's work you can identify the actual bakery.
1 in 5 is 20%.
It's still erroneous.
typo.
Don't forget that without a amalayse that breaks down the starch in grain into simple sugars there wouldn't be any high fructose corn syrup either.
@dabrownman - thanks for posting the link to the two papers, particularly the review of L sanfrancisco. Interesting that they found this bacterium all over the world in various starter samples. This particularly argues against San Francisco sourdough as being 'unique' though there may be lots of sub-species of this particular LAB.
The metabolic pathway for L sanfrancisco is quite interesting and highlights the unique use of maltose as a primary feedstock with the pumping back out of glucose which the yeast can use. It looks like the primary production of acetic acid comes from the diversion of some of the glucose-6-phosphate which gets isomerized to fructose-6-phosphate and resultant acetic acid. Note that this would reduce lactic acid production as less glucose flows through the normal glycolytic pathway. Apparently in culture, some strains can also metabolize fructose though it's not clear whether the requisite phosphorylating enzyme is present. One would have to add fructose to the sourdough as starch is made up of glucose units.
EDIT ADDED: mixinator is correct there won't be any fructose around and even if there is it's still going to dependent on the uptake kinetics between fructose and maltose as to which is preferred. Evolution makes me bet on maltose!
It covers most aspects of building a spelt or wheat starter and what actually happens
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1951026/
There is fructose around for sure and I particularly like this statement in the paper
However, the metabolism of certain sourdough LAB may be influenced by process factors to obtain higher-quality end products. An example of the latter is the stimulated release or addition of alternative electron acceptors (e.g., fructose) or pentosans (e.g., through pentosanases) to stimulate the production of acetic acid (25, 37, 52). In this way, an optimal fermentation quotient (molar ratio of lactic acid to acetic acid) of about 2.5 can be attained (52).
Another interesting note is that like most SD starters in the world these started from scratch ones had no LAB SFin them at all and different yeast in them too.
Happy baking
Of the five bakeries studied by the USDA in the '60s, three were located in Oakland!
rather than L sanfrancisco! :-)
Ha! Funny.
It shoots the claim I make: part of the "magic" of San Francisco sourdough is the use of cable car grease in the dough.
Herb Caen was a very popular San Francisco newspaper columnist. About Oakland he used to say, "The bay bridge has to end somewhere."
I don't know about "soon enough". Who would fund the R&D required for such an undertaking?
Sourdough bakers seem content nowadays to use bakers' yeast to cut down the proofing time and add a little faux sourdough flavoring, or as I call it, eau de sourdeau. The bakeries consider it "close enough" and the public buys it. Why spend money on R&D for genetic modification?
genome was sequenced in 1996. One of the main LAB found in SD was sequences in 2013. The reason scientists sequence genes is to find out what they are, what they do and how they do it - so that they can modify them at will. No worries about money at all. It is happening and we have already seen the results many times.
Yeast that makes opiates and morphine were the most sought after and now - yeast can do that since the yeast was modified using genetic engineering., Home brewers can make beer that has an opiate kick. But it isn't just yeast. LAB Pantarum. a SD LAB has been genetically modified as well to gain a tolerance for ricin one of the big mass destruction chemicals...many others have already been modified to be better probiotics for your gut.
Money is never an issue when it comes to science so long as the research has money making potential.... anything is possible with science it seems