LAB Fermentation - more complete understanding
In another post, we drifted off to a discussion of Lactic Acid Bacteria (LAB). This subject needs a post of it’s own.
The question was posed, “why is it that Yeast Water (YW) doesn’t contain high amount of LAB”? YW are known to produced non-sour tasting products.
Michael, aka “mwilson” replied with an extremely informative and scientifically based answer. Here is a copy from that post.
”LAB fermentation has been utilised for centuries as a way to make foods stable, less susceptible to spoilage and suitable for long term storage.
Many mistakenly think that LAB favour an acidic environment. In actual case LAB are responsible for making the environment acidic. Unlike yeasts their growth is very pH dependent.
SD starters often range between pH 3.7-6 and many SD specific LAB stop growing below pH 4. LAB prefer only mildly acidic environments. E.g. vegetables, grains, meats which are around pH 5-7.5.
Yeast waters will often stabilise at around pH 3.5 since many fruits are somewhere close to this pH. At this low pH, growth of LAB is not favourable.
Other factors relate to nutrition including, available protein sources of which LAB and yeasts generally have a different preference of type.
LAB thrive in SD starters because we bakers refresh them, which brings the pH back up to around pH 6 (the pH of flour). As the dough or batter ferments and become more acidic their growth continues to slow and eventually stops.”
I realized that yeast would reproduce in very acidic environment and also that LAB were unable to do so once the PH dropped to a certain acidic level, but never put 2 and 2 together...
I have wondered for quite a while why YW wouldn’t produce sour tasting bread. Are the microflora that dwell on the fruit identical to those on wheat, since they are captured from the air. Is that the case? Or are the acids from the exterior of the fruit hindering or eliminating the LAB in the microfilm that colonize the outer portion?
The basic question - are LAB present on the outer coating of fruit in the field?
We are fortunate to have a few bakers (you know who you are) that are educated in these types of scientific and biological matters. The details to questions such as these are not easy to come by. We are fortunate to have you. Your expertise, time, and patience with us “normal people” are very much appreciated!
I've not got too many answers, and have an additional question for Michael below. But to your question about LAB on the surface of raw agricultural products, in short yes all raw agricultural products are loaded up with various LAB, yeast, and molds among others. I'm not sure I understand your question though Dan about the acids on the exterior of the foods hindering or eliminating LAB? I don't believe so. Perhaps consideration of the other main environmental factor for microbial growth will help provide a fuller picture. This additional factor is water activity (aW), which for our considerations can be regarded essentially as the "availability" of water in a food. The availability referring to how accessible entrained water is to microbes for proliferation. So while pH has a big impact on the particular flora/fauna of microbes in an environment, so to does aW. For example yeasts in general can proliferate in much lower aW environments than bacteria. So regardless of pH, if there is not enough free water in the environment for bacterial growth but there is sufficient free water for yeast growth, you will find proliferation of yeast exclusively. The inverse can be true too, depending on the specific environments and organisms.
So a question for Michael as well: recently I converted my starter to a stiff one (50%) hydration and was surprised by the additional sourness of the bread. The nose of my ripe starter now is much less acidic, though I'd say the bread is. I had expected that such a reduction in aW would favor yeast over LAB. But based on your other comments I've read about LAB in stiff starters and my experience, I suppose I can surmise that aW even in a stiff starter must still be above ~0.82? If you haven't tested I suppose I could stop being lazy and bring in some starter to test at work.
Ok so the above actually brings me to an additional question as well: do you think it would be possible to maintain a flour based starter with sufficiently low aW to materially limit LAB growth?
“I'm not sure I understand your question though Dan about the acids on the exterior of the foods hindering or eliminating LAB?”
I had a hard time communicating that.
When the microbes, both yeast and LAB come to land on the skin of a grape, do the LAB find an acidic environment that prevents multiplication? Or is the highly acidic environment created once the grape is crushed and added to the water of a YW? Is the outside of a grape acidic to the point that the LAB are hindered or eradicated?
The parameter of water activity (aW) is certainly a key interest where food safety and microbial stability is concerned and while yeasts can indeed handle lower degrees of aW compared to bacteria, attempting to take advantage of this is in respect to maintaining a SD starter is perhaps not practically applicable.
Water activity quantifies available water, i.e. water that is not bound. So you should think of it this way and I would expect, even at 50% hydration the aW would still be greater than 0.9. Note that not all components of flour are soluble.
If you really want to control aW then you would need to consider adding solutes like salt and sugar.
In the specific case of Panettone, the high level of sugar enrichment does significantly decrease water activity to the point that it limits LAB activity. But a flour / water mix that forms a cohesive mass will not significantly limit LAB at any hydration.
Great thank you Michael. Out of curiosity I think I’ll measure aW this week for my 50% hydration starter.
So another question then. I’ve noticed recipes designed to produce minimally sour bread often have higher hydration levains, for reasons explained in this thread. How high can you feasibly go in a flour based starter or levain? I’ve seen recipes up to 125%, but not higher. Assuming of course that you have strong enough flour to survive the higher protease activity. Any thoughts?
This comment caught my eye as I have been thinking about this type of thing myself, from a theoretical point of view.
To over-simplfy grossly, the final dough has to grow and build up acidity to the level where the acidity-loving sourdough yeasts start to thrive and cause the dough to rise (which i am assuming is a relatively constant figure, but I may be wrong on that). The dough is going to have to reach that level wherever it (and the levain) started from. The final flavour of the loaf will be determined by what was in the dough just prior to baking, ie after the acidity reached that level and then carried on increasing during the rising phase.
My dodgy maths suggests that to get to the same final amount of acid, the lower the starting level of acidity, the higher the final population of LABs (there is more work for them to do). This assumes that the total amount of acid produced is based on number of LABs present and time, so is proportional to the area under the population-by-time curve, and that population grows at a constant or increasing rate (this is the bit where my maths lets me down, it is true for exponential and linear growth). So there will be more LABs present at the start of the rising phase, when the acidity is at the threshhold level. They ought to produce more acid during the rising phase than a lower population. So lower innoculations, and lower levels of acidity in the levain, ought to result in more acid in the loaves (assuming the loaves are allowed to rise to the same extent). (This also suggests that adding acidic ingredients to the dough will result in less acid bread, and adding alkali or buffering will result in more acid bread, in fact I think I have read comments to this effect on this forum somewhere.)
Feel free to shoot this down, I wouldn't be at all surprised if it is fundamentally wrong, but it is where my thoughts led me.
TIM
Although it has not been backed up scientifically by me, years of experience has convinced me of the following.
I love sour tasting bread, especially the sour that is derived from Lactic Acids. In order to get that intense flavor profile, the dough is fermented warm (77-79F) at a minimum of 12 or many more hours. Small percentages of levain is always used because the dough will ferment for such an extended time. The huge deterrent to this procedure is the strong possibility of dough degradation. It seems from experimentation that culprit of long and warm fermentation is the exponential growth in acids, more so than hydrated flour without levain. As the acid load increases so does the potential for gluten break down.
With any aspect of dough fermentation, length of time and variances in temperature are major players. Given enough time a slight variance of 78F instead of 75 can make a huge difference.
You wrote, “So lower innoculations, and lower levels of acidity in the levain, ought to result in more acid in the loaves (assuming the loaves are allowed to rise to the same extent).” That’s not been my experience. If dough #1 has 2% Pre-Fermented Flour and dough #2 has 25% PFF, AND they are both fermented at the same temp for the same length of time, the 25% will be much more sour. The 25% will also degrade much quicker also.
I hope some of this helped with your question.
Danny
OH! The following is going to color me a heretic by many bakers.
I don’t think you need a super sour starter to make super sour bread. If I’m wrong, then I’ve been wrong hundreds of times over several or more years. The same way a levain or starter can be over fermented and turn super sour, is identically reproducible with the final bread dough.
Dan, thanks for your experience. You said "AND they are both fermented at the same temp for the same length of time" - my hypothesis was that you fermented them until they rose the loaf to the same extent (however you might measure that - I guess what I meant was "yeast population has increased to the same level"), which would definitely require less time with 25% pff than with 2% pff at a given temperature. My conclusion appears to correspond with your experience - lower percent pff (and the necessarily longer time to wait for the dough to start to rise) will lead to a more sour loaf, as will a lower acidity levain (up, or rather down, to a point beyond which it makes no diff). I think this is because once the yeast starts to do its stuff the LAB population and so rate of acid production will be higher the lower the initial acidity of the bulk dough (that is the conjecture, and the bit that may be completely wrong).
But that was all based on the most rudimentary modelling of what is obviously a very complicated system. And is rather hypothetical because unlike you I have only limited sour tolerance and so don't really have an incentive to try to get it higher, I like loaves made with around 10% pff (less for high wholemeal content) and fermented for around 5 hours at around 27C, which appear to be pretty standard conditions to use. Like you I have had problems with over-fermentation when I have tried lower innoculations left for longer, for example overnight not-in-the-fridge ferments. I do intend to experiment with using yoghourt with sourdough, but I would like to make it myself and haven't got round to that (though I did make my own years ago).
TIM
Tim, what is your goal? How would your perfected loaf taste?
Well I suppose a more complex flavour than a standard bread machine bread, but without excessive sourness, just a bit of a tang. For example, many sourdough loaves from local bakeries are pushing the sourness for my taste, some I like some I don't, but I do appreciate the other flavours that are present, and the chewy texture. That is one thing that drove me to try it myself, I could see there was something there I liked.
Currentlty I am using up whatever flour we have been able to get our hands on, though just recently supplies have become more normal. This has led me to try a bit of spelt and rye in with the wheat, which I like. I also prefer a softer sandwich style bread for everyday use, so mostly I put some butter/oil and skimmed milk in which seems to help keep the hole size even and improves the keeping.
ETA but I am also interested in teh science (I obtained a chemistry degree many decades ago) which makes it all more fun. Or as Lance Armstrong almost said "its not about the loaf". Well not all about the loaf.
Sourness and acidity are two very different things.
Thank you.
Yippee
Acidity is the ability of chemical compounds to donate H⁺ ions, commonly called protons. The more protons the acid can donate the stronger it is. This property is quantifiable, you can look up acid dissociation constants, pKa, and get an idea of how acidic a compound is. The lower pKa is, the stronger the acid, so lactic acid with pKa of 3.86 is stronger than acetic acid with pKa of 4.75.
Sourness is the ability to perceive sour taste, it’s a complicated biochemical mechanism and it is not entirely understood to this day. It is connected to acidity but it is not necessarily determined by it. For example, fermented dairy products, like yougurt or kefir, contain about 1% of lactic acid and have pleasant mild taste. On the other hand, 1% acetic acid, oh, you would not like that at all, it tastes harsh and is much more sour.
Yeasts, LAB, and many other microorganisms will be present on the on skins of fruit. The microflora of environments found in nature will be diverse. Human interventions will decrease diversity as you apply selective pressures.
The exterior of fruit will not be acidic since the acids are within the fruit pulp, along with the sugar.
The microbes on skins are lying in wait, an opportunistic pit-stop if you will...
Since we learned that the acidic environment created from fruit hinders LAB, would using some portion of an acidic liquid, such as pineapple juice or another such acid during refresh ward off the LAB and allow the yeast to flourish?
When thinking about it, it seems that because LAB are hindered in a YW, they are more powerful at producing gas because the yeast are maximized. My understanding of what Debra taught me is that if the yeast are maximized, the LAB are minimized and vice versa.
That's easy to check - mix up some starter and let it run its course well past the peak. If acidity hinders LAB more than yeast, then acid production will stall and yeast will proliferate, evident by the increase of gas production. Basically, the starter should foam. If, on the other hand, it's the yeast that are more sensitive to acid, then gas production will stop, while acidity will continue to increase. In this case the starter will go flat, and get so sour that opening the jar will make your eyes water.
Concentrated Lactic Acid Sourdough is a Russian bread technology introduced to us by Yippee. You can read about it here:
http://www.thefreshloaf.com/node/59914/20190414-100-rye-rus-brots-high-tech-clas-concentrated-lactic-acid-sourdough
This is a rye-flour-based ferment designed to maximize lactic-acid-producing bacteria, and reduce or eliminate other organisms, including yeasts. It is used in combination with commercial yeast. It is more stable and easier to maintain than a normal sourdough culture that can both sour and raise bread.
What's interesting to me is that in fermentation pickling of fruits and vegetables we use salt to inhibit other bacteria and yeasts and to favor the lactic-acid-producing bacteria, but in the CLAS we only manipulate hydration and temperature to get the same effect. It seems to me that the yeast water process is like CLAS in reverse: it favors the yeast, not the LAB.
The question I have is: are we hoping with our grain-based yeast waters to develop a ferment that will both leaven bread and sour it, like a traditional sourdough?
Because grain is less acidic than fruit, do we hope it will allow the LAB to flourish in concert with the yeast, rather than, as in a fruit-based ferment, favoring the yeast much more heavily?
Another notion that occurs to me is that a liquid ferment of commensal yeast and LAB sounds an awful lot like keifer. A quick literature search reveals that keifer culture immobilized in a matrix of processed corn has been used to successfully make sourdough bread.
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1750-3841.2012.02985.x
Perhaps we should be looking into keifer recipes as a starting place for developing an easier sourdough starter. Or kombucha.
Danny,
Does anybody have any evidence that the yeast comes from the air? I have always considered that to be a wives tale since National Geographic did their experiment with sterile flour in Egypt and totally failed to get a sourdough starter to form. In the end they got some starter from a local baker and assumed that it was representative to the sourdough thought to have been used to bake bread for the pyramid workers.
Doc, you may have mis-understood me, or I miscommunicated. But maybe not. I am under the assumption that both yeast and LAB (spores I guess) can be air borne. I’m not talking about making a starter and trying to “catch” yeast in the air. I believe those microbes come from the flour. The sterilization test bares that out.
I am talking about the microbes that reside on wheat, fruit, and other such plants. I am under the impression that those microbes were airborne before they found residence.
If thoughts are crocked or bent, please set me straight. <LOL>
Danny
Here's one possible explanation... they are delivered to the grains and fruit by bugs. In their poop.
https://www.popsci.com/why-san-francisco-sourdough-tastes-so-good/
Even the originator of the "theory" does not claim to have any supporting evidence (other than "it makes sense"). But the plant science community commonly grows plants in sterile environments so it should be testable. And there are many different yeasts and LABs that show up in starters around the world so they might be propagated by a local insect population.
I just don't know because nobody has presented any convincing evidence for an soil-borne or seed-born or airborne source (or perhaps it is really in the air and gets brought to the plant by rain). When I make sauerkraut, I take off the outer leaves of the cabbage until the remainder is clean, but there is always plenty of leuconostoc mesenteroides to make lactic acid and CO2 within a day. And when I make idli, I wash some the dal and let it sit in water in a warm place for a few hours to make sure that there is enough native LAB to begin the fermentation even before I soak the main batch (photos of good result here, bad result here). Where does the LAB hide? It seems to be inside of the skin of the black gram so it may be co-resident in the live plant tissue. As it stands it remains a mystery and not a secret (unless there is a paper out there that presents credible data).