The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts


petercook's picture


Hello All,  I'd like to get a few points straight in my mind. Perhaps you can help? I have been reading up on preferments (not a sour dough starter). In both Rose Levy Beranbaum's the Bread Bible and Daniel T. DiMuzio's Bread Baking they talk of Homofermentive and Heterofermentive bacteria. When discussing preferments they both say that these bacteria are present in the environment, but which environment they don't say-- flour, yeast, air? Surely not the water or salt. ! And my 2nd question: they say that the kind bacteria you develop (in the preferment) is determined by A. the hydration of the preferment, B by the temp and C. by the amount of time you ferment. Ok fine. I've got that but here is the tricky part, They say that once the flour, water and tiny amount of yeast come into contact then the race is on between the yeast which propagates quickly and the bacteria which propagates MUCH MORE SLOWLY. Ok, again, I've got that but exactly how can I consistantly produce the homofermentive bacteria in sufficient amouts to make my bread taste good. So, What exactly is the formula for producing the MILDER homofermentive bacteria thus obtaining lots of lactic acid in a preferment? This is what I've been doing but I know it's not quite right. 1/4 cup water, add 1/8th tsp of dry yeast, stir and set aside. Combine 90 gr of unbleached bread flour with 10 gm of W.W. flour add 100 gm of water and only 2 tsps of the yeasted water (through the rest away). Stir well for 2 min, cover and let rest at room temp (70 F) for 18 hours. I then proceed with making my dough at a 65% hydration. So, how can I give the advantage to the bacteria and not the yeast? Thank you

Doc.Dough's picture

The long fermentation may improve flavor but there are no bacteria to speak of in your dough unless you include a sourdough starter in the mix and I don't see it in your process.


proth5's picture

was made by Doc.Dough above.  In general, although bacteria is present (in the flour) unless you are doing a sourdough - they simply don't come in to play (much - there is much to consider on this topic, but in general we discount the bacteria in commercially yeasted pre ferments).  What you are doing with a commercially yeasted pre ferment is producing fermentation flavors, acids, and playing a bit with protease action.

A liquid commerically yeasted pre ferment will emcourage protease action which degrades the gluten slightly and increases extensibility.

A firm commercially yeasted per ferment will give acids without the high amount of protease action which will encourge "strength" in the dough.

Mr Di Muzio understands the above much better than I and I would not expect him to write otherwise.  Your talk of homofermentive and heterofermentive bacteria tells me you may have wandered a bit in your reading - so go back to the source and make sure you are reading about commercially yeasted pre fements  (you'll see words like "poolish" or "biga" or "pate fermentee") and not sourdoughs or levains.

If you want the unique qualities that these various bacteria provide - I'm afraid you have gone into the world or sourdough and sourdough starters.  Debra Wink has written much on this topic on these pages (she also recently taught a class on these at the King Artur Baking Education Center) - use the search function to find her work. 

Hope this helps.

petercook's picture

I thank you for your input. However, the reason I am so concerned about the 2 types of bacteria is what DiMuzio says: "We mentioned previously that BACTERIA need time to develop in number and contribute their acids to the strength and flavor profile of bread dough. Unlike yeast they can't be hurried along, and bread making procedures that ignore that fact are usually doomed to create bland, uninteresting loaves".  Be assured that Mr DiMuzio has not yet mentioned levain or sourdough. On the subject of preferments using yeast he says, "bacteria are primitive one-celled organisms placed wthin the Monera Kingdom. The types of bacteria common in bread dough consume the same simple sugars used by yeast calls. The primary by-products of BACTERIA in dough formation  are of 2 types of organic acids: lactic acid and acetic acid... the types of BACTERIA that produce these acids can thrive in temperatures of 50-90 F. and are collectively referred to as Lactic Bacteria. As baker's we are concerned with 2 categories of lactic bacteria: Homofermentative bacteria and heterofermentative bacteria... If you want your bread to develop good handling properties naturally and to taste good, you MUST pay as much attention to the quantity and type of BACTERIA in your dough as you do the activity of the yeast."  Later in the chapter he says, "Unfortunately, bacterial formation almost always proceeds more slowly than yeast formation- MUCH MORE SLOWLY."  He then proceeds into a discussion on enzymes and esters but later, in the discussion of manufactured yeast preferments he says, just to quote a few remarks, "...the extended fermentation time (of a poolish) ensures enough bacterial development" On the subject of making a biga he says, " It's extremely dry consistency makes it an ideal envirnment for heterofermentative bacteria and the sharp acetic acids they produce."  Now I don't wish to be argumentative but it sure sounds to me like those bacteria are a great big deal. Please note that he has not yet even begun to discuss levains and sourdoughs. All of the above refers exclusively to manufactured yeast preferments.

proth5's picture

that's fascinating - truly.  I have been involved in some discussions about bacteria in commercially yeasted pre ferments (as I alluded to) and I was unaware that he was making such a big deal of it (since I don't have his book).  Yes, one does get bacteria in these pre ferments, but usually the elapsed time is so short that one doesn't get all wrapped up in it. I've worked with other bakers (who are - believe me - as qualified as Mr DiMuzio) who never really bring the discussion around to managing the bacteria in commercially yeasted pre ferments - leaving that discussion purely for sourdough.  In fact, my discussions mostly wound around to having folks advocate using salt in commercially yeasted pre ferments to control  and lessen the growth of bacteria. So, I am now puzzling a bit.

I'm not sure they are a "great big deal" as you say.  Again, the folks I have worked with don't seem to sweat the bacteria in the commercially yeasted pre ferments and they produce some nice bread.   

But - to me, it seems like he has given an answer to you - use a poolish for its lactic qualitites and a biga for its acetic qualities.  Use very small amounts of yeast so that the maturation process takes longer and don't salt the pre ferment. (In fact, going way out on the edge here - use no yeast and let the mixture mature over a couple of days.  This is the beginning of a sourdough starter and you will have plenty of bacterial action - although just which bateria we may not be certain...)  You might also want to ferment at higher temperatures which will encourage bacterial growth (so, at a higher temperature - very tiny amounts of yeast).  On the flip side, my decision process would be to use a poolish to add extensibility (which is a handling quality) and a biga to bring strength (again, a handling quality) to a weaker flour, a whole wheat or whatnot - without the thorough consideration of bacteria.  Since I am aiming for 8-12 hours to reach maturity and I do this at relatively low temperatures, I'm going to say that I'm not specifically encouraging bacterial growth and don't think much about it (even if it is happening). Exact formulas?  If anyone could do that, we could dispense with this whole process of constant observation and evaluation and just let machines do it.  And if I could do it - I wouldn't post it here - I'd be funding my retirement by selling it. You have a process and a formula - you need to evaluate the taste and handling qualities and adjust given the guidelines.

I would not expect either to have the bacterial action of a sourdough, though. And as I think about it more - one of the reasons we cultivate a sourdough culture is to get the bateria that best works with wild yeasts and that bring the "best" flavor to breads (My goodness, the energy that we expend to get the "right" lacto baccilli!)  Again, I puzzle mightily about giving great consideration to bacteria when the "culture" is at its very early stages when we could be growing just anything.

Again, what you quote is fascinating from this regard.

Mr DiMuzio and Ms Wink do check in from time to time, so hopefully that will post and give us some good information.

Hope this helps and thanks for the clarification.

petercook's picture

I'd certainly love to hear more on what Mr. DiMuzio has to say on this topic because I've worked mightely trying to get the depth of flavor he speaks of. Thanks to all for your input. Now that I think about it, it is not surprising to have vastly differing opinions on bread making. Just something so straight forward as making a sponge results in literally scores of formula by different authors (every hydration from 60% all the way up to 151% hydration). It's amazing that we can communicate at all.

proth5's picture

putting some more thought into this - one factor in achieving flavor with pre ferments is the % of the total flour that is pre fermented.  You didn't describe this in your quick formula - so you might want to consider it.

There is a school of thought that relies pretty heavily on sourdough.  I've been using two pre ferments - one sourdough, one not in a lot of my breads.  This gives a flavor that people rave about...

It's all fascinating...

Doc.Dough's picture

Let's just go back to biology and math to look at what can happen and then draw conclusions about what is not happening.

The yeast population in a mature dough is something on the order of 10E5 (100,000) per gram and the bacterial cell count in a mature sourdough is about 10E7 per gram.  The population doubling time at conventional process temperatures (20-25°C) range from 2 to 4 hours for both yeast and bacteria.  The combined naturally occuring yeast and bacterial populations in commercial flour is well below 100 per gram (which you can verify by isolating a sample of wet flour for long enough to see/smell the result). At levels below about 100,000 per gram the impact is negligible. So the question is how long might it take to grow 100/gm to 10,000,000/gm where it will actually produce enough acid to stop the growth process when the doubling time is ~3 hrs. The population ratio you need is 100,000 which is about 17 doublings plus about one additional doubling time for the cell growth mechanisms to be constructed by the initially inactive constituents.  So we would have to wait for 18 x 3 hrs = 54 hrs to have a significant population of bacteria, and the initial yeast inoculation will have consumed all of the available sugars in your preferment within 16 hrs irrespective of how little yeast you try to add to the initial mix.  So at 18 hrs (1 doubling time to get ready and 5 to grow) you have at most 100 x 2^5 = 3200 bacteria per gram of preferment made with commercial flour. 

Your commercially yeasted perferment does not contain a significant amount or bacteria - irrespective of what you read in a bread book. Both the chemistry and the biology are dominated by the commercial yeast that you started it with.

proth5's picture

semi-skilled labor in all of this, and Doc.Dough, I do understand your illustration and reasoning.  This is why I've held to pretty much the line on "we don't invest much thought into bacteria in commercially yeasted pre ferements."

But I do recall having a long and involved discussion on these pages with Debra Wink about using salt in commercially yeasted pre ferments to lessen bacterial activity (under certain circumstances - that is -  a very warm environment).  She constitutes skilled labor in this discussion.  I remember it because we argued long and hard and in the end I saw her point. (Although I have never encountered this need given how I mix and tend my pre ferments.)

Again, not that I think this is something we should consider so deeply for our bread baking routine.

I'll question a little that the yeast would consume all the sugars in a pre ferment in 16 hours irrespective of the amount of yeast - surely (and this is in the realms of the theoretical, I'll admit)it seems that one granule of yeast in 20 pounds of flour would not do so.  Somewhere between that ridiculous example and what we commonly mix up as pre ferment, might there not be the possiblility that you could let the thing sit around long enough to get bacterial action?  Again - nothing that I would do, personally, but if someone really wanted to?  Given that bacteria can grow even over the life of a normal pre ferment, isn't it possible? I know that wild yeasts are different, but yeast and bacteria exist quite happily in the same bucket of goo and become stable for long periods of time - is it really impossible?  Or am I (as is often the case) missing something?

I'll be in violent agreement with you that if you just take a flour and water mix and let it sit for a couple of days (about the same as 54 hours to us semi skilled folks) you'll have plenty of bacterial action.  But even if you did that, the question would be "are these really the bacteria that we want?" as what I understand tells me that it will be an assortment - some of which will bring "nice" flavor and others not.  My understanding being that is takes time and special conditions to get those bacteria that we treasure so much for our bread.

I suppose I'm keeping this alive because Mr DiMuzio does occaisionally chime in on this forum.  He's a very knowledgeable baker and one ponders why he makes such a big deal of the bacteria.  I would take this to another forum, but it is not a first hand citation for me, so I don't want to quote or question without his book in hand (and it is not easy for me to get right now...)

Thanks for your response - it kind of confirms what I intuited...

Doc.Dough's picture

The case as presented was:

1/4 cup water, add 1/8th tsp of dry yeast, stir and set aside. Combine 90 gr of unbleached bread flour with 10 gm of W.W. flour add 100 gm of water and only 2 tsps of the yeasted water (so there is at least 1/24 t of yeast in the preferment which is only 200g total)

The preferment was allowed to grow for 18 hrs (4 to 9 doublings depending on temperature).

Yeast will grow happily until they have exhausted the supply of sugars that they can metabolize and that is what happens.

Yes, if you don't add any yeast (or your microscopic one granule which is not trivial and probably trumps all of the native species) then it will take longer.

Yes, the particular mixture of "wild" yeast and bacteria in a batch of flour is unpredictable (well only sort of unpredictable - it is often dominated by Leuconostoc and other things you don't really want).  And Debra Wink has been right in almost every case I can remember so I tend to trust her recommendations until I can track down the authoritative source (or not).

However, I have been misled often enough to demand that real science support anecdotes (the plural of anecdote is not data) since backing your mental model out of a blind corner can take a long time if you don't suspect that there is something wrong with your world view.

I have neither Mr DiMuzio's book nor his email address so until he voluntarily pops up and provides clarification, I will lean on the biology, chemistry, physics, and math that have for so long formed the basis for understanding food.

proth5's picture

completely stubborn here - just not a biologist of any stripe and trying to hammer an understanding into my head - always helps to discuss and question. I had moved away from the specific formula and gone on to generalities (and maybe didn't make that clear).  The case as presented was "this is what I am doing and it doesn't work" - so I was trying to envision alternatives.

As an aside,  I know that Debra got a little frustrated with the thickness of my skull, but in the end, she had solidified her thinking and I had (finally) learned something.  Seems like a good thing in the long run.  Deep breaths...

Yes, all my sourdough knowledge tells me exactly what you said - that the stuff (a semi skilled labor term :>))growing at the early stages of a culture is what we really don't want.  So that begs the question why anyone would want to encourage it and bake with it.

But both yeast and bacteria do grow - together - in a stable sourdough culture (don't they?)  I seem to have a vague memory that the yeast doesn't simply consume all the available food and out compete the bacteria because they are digesting different types of sugars - or one breaks down the starches for the other, or for some good reason.  I just can't quite remember it and can't find it right now in my reference material.  Thought that you might know.  I'll need to look further, I guess.  Is the difference that once one has introduced commercial yeast (which I know is different from the yeasts that we find in sourdough) - its growth is so strong that the bacteria doesn't have a chance?  (Or just that it can't reach a "meaningful" level?)   That seems to contradict what Debra so painfully got into my brain - that it was quite possible that bacterial action can happen in a commercially yeasted pre ferment (say, if it is maturing in very hot conditions) and that salt can be added - not only to slow yeast, but to slow the bacteria.  It was a hard fought battle and I'm still hanging my hat on what she said.

Again, I think you and I agree about the triviality of the bacteria in a commercially yeasted pre ferment and that from a practical standpoint, we shouldn't be troublig ourselves with it. I'm trying to wrap my mind around things.  I have a bad habit of asking question because I really do want to know the answers and understand. I 'm not completely sure how anecdotes got brought up, but I agree that they aren't knowledge or data.  But for some reason, once we get to this biology of bread making, the knowledge comes pretty hard for me.

Probably what is confusing me the most is that Mr DiMuzio took the time to write this stuff down - in a book - dealing with the background for artisan baking.  I don't think he is the sort of individual to be deliberately misleading and I'm am hopingthe repeated mention of his name causes him to chime in.


Doc.Dough's picture

The best way to understand the factors that are in operation in a stable sourdough culture is to read (and re-read about 40 times in my case) the seminal paper by Michael Ganzle (available in full text at the link below):

July 1998, p. 2616–2623 Vol. 64, No. 7
Modeling of Growth of Lactobacillus sanfranciscensis and
Candida milleri in Response to Process Parameters of
Sourdough Fermentation

I have (accidently) run the experiment in which you start with a commercially yeasted culture and feed it flour and water every 12 hrs  (for about a week as I remember), and one day discover that it is pretty sour and from then on behaves exactly like a sourdough starter.If you learn anything from Ganzle, let it be that the LAB grow faster than the yeast at all temperatures of interest; that the LAB stop replicating when the pH drops to somewhere around 3.8 and stop metabolizing sugars when the pH drops to about 3.5; that the growth rate of the LAB and yeast are about equal at a pH of 4.3 (which drives you to assure that your post-refresh pH is above 5.3 so that the LAB has an opportunity to built up its population before it ceases to replicate at pH 3.8); that the yeast is insensitive to pH and acidity in general (within the normally encountered range); that the LAB and the yeast behave independently as they respond to temperature, pH, ionic strength, acetate, lactate, ethanol, and acetic acid concentrations).Other papers teach that the availability of various sugars in autolysed wheat flour doughs is more maltose than glucose, and that both LAB and the important sourdough yeasts will consume both but have preferences about what they consume first.In a sourdough culture the yeast and LAB do not grow together; they grow sequentially.  The dynamics of sourdough always starts with the LAB consuming part of the available maltose, outgrowing the yeast, producing acid, driving the pH down and limiting their own ability to reproduce, after which the yeast is left with lots of glucose and little competition, proceding to consume the glucose to exahaustion and leaving maltose to support browning of the crust.There is also work that demonstrates that a mature sourdough culture by adding commercial yeast has no lasting effect since the commercial yeast can't outcompete the organisms that have developed a happy symbiosis and soon loses out as the population density declines exponentially to insignificance over multiple refresh cycles. (this is an experiment you can easily run on your own - just allow seven days and 14 refresh cycles).Read the paper.  Do the math. Strive to understand why the models are independent. Study the cross partial derivatives to see where there are self-imposed limitations on population densities and what a limit cycle looks like if you refresh at low ratios (1:1:1) or high ratios (1:30:30) and what difference it makes if you refresh too often (before the population density stabilizes).
proth5's picture

for the link.  I have read some Ganzle, but this area (for me) is one of those where knowledge doesn't sink in too quickly.  Maybe on my 50th read :>)...

And thanks for the refresh on why the bacteria and the yeast exist together in a stable sourdough culture.  Maybe this repetition is the one that will get me to remember it. 

Anyway, I "kinda" knew that once you have a stable sourdough culture, addding commercial yeast will not change it much (which is why I have seen "my teacher" make a big show of not "contaminating" the sourdough, sporting a wicked grin that told me that it didn't much matter...)

And yet, we are still left with the mystery of why a reputable baker would advocate the cultivation of the bacteria in a commercially yeasted pre ferment.  Sigh. That's going to bug me...

PMcCool's picture

I had intended to sit this one out, since I don't have the book in question.  However, from the preview that is available on line, I come away with somewhat of a different point of view.  It does not appear that Mr. DiMuzio is emphasizing bacterial fermentation as part of a fermentation utilizing commercial yeast.  Rather, that section of the book addresses the various forms of fermentation that are available to the baker.  If I have read and understood correctly, then all that Mr. DiMuzio is doing is telling his readers how to achieve specific results by manipulating environmental factors.

Given my current state of knowledge, there is no practical way to utilize bacterial fermentation except in the context of sourdoughs.  Please note that the sample of text which could be previewed did not mention salt-rising fermentation, another bacteria-driven ferment.  Consequently, I think the idea that we should expect significant bacterial contribution for a dough leavened by commercial yeast is not supported by Mr. DiMuzio's text.

My two cents.


proth5's picture

for that.  I feel better now...


Song Of The Baker's picture
Song Of The Baker

Me bake bread.  It good.  All I know. Unga!

You guys are too good!