The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

low hydration + cool starter index

headupinclouds's picture
headupinclouds

low hydration + cool starter index

Yeast vs LAB lag phase (may be relevant to Desem starter optimization)

Debra Wink writes:

Reducing sourness can be accomplished by shortening the refreshment cycle, not because of aerobic vs anaerobic, but rather by taking advantage of the disparity in lag phases between yeast and lactic acid bacteria (LAB). Bacteria reproduce faster than yeast, but yeast have a shorter lag phase. The lag phase is that time between refreshment and the start of population growth (reproduction). The organisms need a little time to sense their environment and re-orient themselves to the change that refreshment brings (pH, nutrients, waste products, etc.) before they begin growing again. For LAB it takes longer, so yeast start growing first. Each time you feed, it starts a new lag period. If you stop the refreshment cycle short, so as to keep the LAB from taking off, you give the yeast a little advantage in the race by cutting the LAB off at the knees.

You can't completely eliminate LAB, but you can reduce the sour by cutting their numbers.

mwilson writes:

While I'm sure LAB do encounter longer lag times compared to yeast, bear in mind that the higher the inoculum the shorter the lag..

I did find a paper that looked at the cell numbers of LAB and yeast during the refresh cycles of lievito madre done for panettone production. The starting ratio from storage was 10:1 (LAB:yeast). After each of the short-time (4 hours) refreshes the ratio shifted towards 100:1 (LAB:yeast). So based on that evidence this high inoculum (small feed) and short duration didn't favour yeast at all, it favoured LAB.

Feeding this way cuts back on acid, that's what it really does. LAB have no problem holding their own and will typically always outnumber the yeasts.

100:1 is a standard and stable ratio.

 

Liquid vs firm sourdough:

Debra Wink writes:

So, why does my firm starter produce milder bread than my liquid one, when firm starters have a higher percentage of acetic acid? Because it has a lower total acid concentration. More specifically, the bacteria grow slower in a dry starter, so their population shrinks over multiple refreshments (yeast seem to hold their own).

Debra Wink writes:

In general, when baking with 100% whole wheat, what % of the total flour do you try to pre-ferment

In general I don't care for sourdough's acidity in whole wheat breads, so I don't make them. I tried desem for a while, and it was milder, but I wasn't loving what, to me, seemed like a strange flavor. The things that promote mildness, aside from keeping the starter at cave temps like desem, is keeping it very stiff, feeding 3 times a day leading up to mixing your dough, use as little prefermented flour as will do the trick (11-18% probably), and try to get it from mixer to oven in about 6 hours or so. There are a lot of enzymes in whole wheat, and they will break down the dough if you take fermentation out too long. But this varies a lot from one brand/type ww flour to the next, so you just have to experiment.

Population dynamics http://www.thefreshloaf.com/comment/95232#comment-95232

Debra Wink writes:

By "strength," in this context, I think what we're really talking about is the collective power of the yeast to huff, and to puff, and to blow the bread up :-)  In other words, a strong rise, or rising power. It is the yeast fraction in the culture that provides the lift. Lactic acid bacteria (LAB) could raise dough in theory, but in practice, they fall flat. So, a good rise is all about healthy, vigorous yeast. Bacteria contribute acids which flavor dough, but also play a big part in gluten structure and rheology. In the short term acid tightens gluten, contributing to dough strength, but in the long term, it accelerates proteolysis, contributing to its breakdown. And it adds sourness that is not welcome in all breads. You'll find yeast/lift at one end of the starter spectrum and bacteria/sourness at the other. You can't maximize both at the same time; one comes at the expense of the other. Where you want your starter to be on the spectrum, depends on the bread you are making. For panettone and pandoro, it sounds like maximizing lift, and minimizing sour is the goal.

I think the key to understanding starters, is to recognize that population dynamicsand metabolic effects are two separate, albeit related issues. Population dynamics have to do with organism numbers, and how they interact and fluctuate in relation to each other and to their starter environment. Whereas metabolism is about what those organisms aredoing, and what effect that has on the dough. The magnitude of those effects are related to the population numbers. But the numbers are regulated largely by how hospitable the sourdough environment is to the various species, and how much antagonism there is between them. Does that make sense so far?

Dan gave us a good overview of howdoughis affected by hydration (some cereal chemistry as well as metabolic effects), but now let's take a look at how thecultureis affected---the population dynamics---because that will determine themagnitudeof the metabolic effects. Lowering hydration will slow all the microorganisms, yes, but yeasts are not quite as sensitive to it as the lactobacilli. In other words, the growth rate of the bacteria declines more sharply than that of the yeasts. Sourdough LAB thrive in warmth at high hydrations; low hydration and cool temperatures really slow them down. Yeast benefit from this, because they have less competition from the bacteria, so they have more space, and the resources to expand. They aren't quite as hindered by low hydration, low temperature, low pH, salinity, etc., as lactobacilli are, so even if they do slow some, they gain an edge because the bacteria are slowed more. And the one thing that yeast are more sensitive to than lactobacilli---acetic acid---is reduced as the bacterial population shrinks. So, when you knock back the bacteria, yeast tend to flourish, and rising power increases as sourness decreases.

But the key to it all, is multiple refreshments. It's the regular dilution through feeding that shrinks the bacterial population here, because they aren't keeping pace with the yeast, relatively speaking (and starter ripeness, and readiness for feeding is determined by yeast rise and fall). Because it takes some time for the populations to change and re-stabilize, a starter maintained firm (and fed frequently) for at least a week is probably going to give you better results in your panettone than a liquid starter, even one that is firmed up "as needed." It's the difference between a true firm starter, and a firm pre-ferment. The effect will be different, because the populations are different. In a firm culture, you are actually manipulating the starter environment to suppress bacteria (sour) and enhance yeast (lift), whereas a firm pre-ferment is more about manipulating the metabolic effects to increase acetic acid. See the difference? A culture maintained firm will give you less sour (and more lift). A firm pre-ferment made from a liquid starter may give you more. The magnitude of the metabolic effects reflect the relative differences in population numbers.

 

Lievito madre: http://www.thefreshloaf.com/node/61925/my-lievito-madre-videos

 

mwilson writes:  

 

Generally speaking, a high inoculum will favour a more lactic flavour while a small one will open the door for more acetic acetic development.

 

Q: How do I judge maturity of a low hydration (e.g. 50%) whole grain starter as used in Desem, and what is an optimal maintenance schedule?

Notes:

Open crumb w/ 100% spelt bread:

 

Comments

Debra Wink's picture
Debra Wink

While I'm sure LAB do encounter longer lag times compared to yeast, bear in mind that the higher the inoculum the shorter the lag.

This is true. Also, the higher the temperature, the shorter the lag.

I did find a paper that looked at the cell numbers of LAB and yeast during the refresh cycles of lievito madre done for panettone production. The starting ratio from storage was 10:1 (LAB:yeast). After each of the short-time (4 hours) refreshes the ratio shifted towards 100:1 (LAB:yeast). So based on that evidence this high inoculum (small feed) and short duration didn't favour yeast at all, it favoured LAB.

I have a different perspective on this. If 100:1 is the stable ratio in this LM refreshing regimen, then that's where the story begins for me. How the LM was prepared for storage, and what the storage conditions (refrigerated?) and duration were are important details, because those are the factors that brought it to a ratio of 10:1. And when the refreshment feeds were picked back up (at warm temperature?), the culture recovered to its former equilibrium. Temperature plays a role in population dynamics too. LM is refreshed warm, and LAB love warmth, which helps them recover. When looking for evidence on any one parameter, the impact is clearer when all the others are kept the same, and that isn't the case going from storage to fully restored.

Feeding this way cuts back on acid, that's what it really does. LAB have no problem holding their own and will typically always outnumber the yeasts. 100:1 is a standard and stable ratio.

100:1 is on the lower end of what is typical/common for traditional (type I) sourdough starters, and in that respect it does favor yeast. I would expect it to be relatively light and mild compared with 1000:1, which is also common (and anything in between). Either can be stable or unstable, depending more on consistent maintenance than any particular ratio. And some starters have been found to extend even beyond this range -- at both ends. Lievito madre is a specialized starter, and its particular balance, as for all starters, comes as a result of its total maintenance regimen and the subset of microorganisms within.

All the best,
dw

headupinclouds's picture
headupinclouds

I appreciate your clarifications on this as I continue to try to piece together a practical understanding on the matter.  I have been thinking about a related issue, and give your background (and Desem experience), I can't pass up this opportunity to ask a question.  I've been maintaining a cool (50-60F) low hydration (60 %) starter for the last few weeks to bake Desem as a daily bread with various changes here and there.  My initial searches came across more of the mechanics than the underlying background, and I created this page as a personal reference to store bits of relevant discussions from various TFL threads as I tried to piece it all together.  Perhaps I will clean this up a bit once I have a better grasp on it.  In this Desem post by JMonkey, he states the Flemish bakers did the following to create the particular mild flavor of whole wheat sourdough bread they were after:

1. They kept their starter firm.

2. They kept their starter cool (50 to 60 degrees F)

3. They used quite a bit of starter so that the bread would rise quickly and the bacteria would not have much time to produce a lot of acid.

The first point is addressed by you in a discussion referenced above ("So, why does my firm starter produce milder bread than my liquid one"...).  As a practical matter, I have found the low hydration starter also seems to delay proteolysis, and the mature starter seems to have lots of viable gluten by the time it is used, which is especially helpful in the context of whole wheat baking.

The second point is less clear to me.  I have frequently come across posts stating LAB:yeast reproduction rates are highest in a window of approximately 72-75 F (I understand one can't use absolutes with anything as variable as these starters are), and that lower temperatures actually tend to favor LAB reproduction (and presumably their metabolism and acid byproducts).  This seems inconsistent with a 50-60 F maintenance temperature -- at least in terms of the target flavor profile itself.  There may be other benefits to this that are notable, such as further slowing down proteolysis and other adverse enzyme reactions attributed to whole wheat.   I have also found the lower temperatures support a convenient 1x per day feed cycle with a wider "ripeness window", but I suspect I'm missing something else important here.  Perhaps these LAB:yeast ratios do not apply to such low hydration starters?

The stated motivation for the third and final point is that a larger percentage of preferemented flour results in a faster rise, with less chance for acid build up.  This seems to be consistent with a desire to exploit the "disparity in lag phases between yeast and lactic acid bacteria"  that you mentioned, however, one thing puzzles me.  When you are discussing Desem later on, you mention the following:

the things that promote mildness, aside from keeping the starter at cave temps like desem, is keeping it very stiff, feeding 3 times a day leading up to mixing your dough, use as little prefermented flour as will do the trick (11-18% probably)

You seem to confirm the lower temperatures are desirable for Desem (the second point in JMonkey's summary), but when you talk about using "as little prefermented flour as will do the trick", this *seems* to be in conflict with the relatively large amount of prefermented flour he suggests (30%).   Any input you could provide on this apparent discrepancy would be much appreciated.

 

Debra Wink's picture
Debra Wink

I can address them here and there in pockets of time, so this will come in bits and pieces over days. But firstly, the very best resource for desem background and process is The Laurel's Kitchen Bread Book by Laurel Robertson, Carol Flinders and Bronwen Godfrey. Laurel devotes 25 pages to desem. Keep in mind that it was written in the early 1980's, and is not any sort of scientific authority. But I think it's still a valuable resource for whole grain bakers.

I have frequently come across posts stating LAB:yeast reproduction rates are highest in a window of approximately 72-75 F (I understand one can't use absolutes with anything as variable as these starters are), and that lower temperatures actually tend to favor LAB reproduction (and presumably their metabolism and acid byproducts).  This seems inconsistent with a 50-60 F maintenance temperature -- at least in terms of the target flavor profile itself.

You're going to come across this and related fallacies over and over, because a variation on this theme has been taught in classes and published in too many baking books. In other words, it's not going away any time soon. But it is untrue. Sourdough LAB thrive in higher temperatures, which is where they reproduce the fastest. They slow way down at temperatures in the 60's and 50's, and that (and low hydration) are what keep the whole grain desem starter from getting too sour. The misunderstanding comes from the observation that the ratio of acetic acid to lactic acid changes at lower temperatures, leading to an assumption that this is because acetic acid producers grow better in those conditions. But they don't -- and they aren't a different kind of bacteria. They just change what they're producing when conditions and resources change. Microorganisms are adaptable that way. And a higher ratio of acetic acid doesn't necessarily mean there's actually more acid or more sour. It's a relative thing, not an absolute one. And one that is probably moot in desem anyway, because there are plenty of resources in whole grain flour to produce acetic acid regardless of temperature. But a well-maintained desem is mild because the bacterial population is reduced and kept in check. Less bacteria mean less acid.

headupinclouds's picture
headupinclouds

Thanks for the reference.  I'll read through Laurel's review of desem carefully to see if I'm missing something.  I found a few posts (including a post from you in 2009) suggesting that the lengthy authentic desem starter build she describes (10 lb bag of flour, etc) could effectively be replaced by a low hydration and low temperature conversion of an existing starter with frequent enough feeding to avoid acid build up.  I had already been keeping a 75% hydration room temperature whole wheat starter, so it seemed like a natural adaptation.  Mine has been in the low 50's with daily 5:6:10 feeding for a few weeks.

Thanks for the correction on the LAB temperature preference.  I was doing all sorts of mental gymnastics trying to unify this 72-75 F window with core desem principles.  I'll sleep more easily now that the answer to this puzzle is so simple.  I appreciate your response on this, and there is certainly no rush.  I know how time consuming these technical explanations can be, and you seem to get pulled into them fairly often.

There was one other potential explanation or motivation for the large preferment from JMonkey's post, which is relevant to whole grain baking in general.  In the spirit of this loosely organized desem brain dump, I'll include it here.  In the theory chapter (III) of Peter Reinhart's Whole Grain Breads, he states:

Pre-fermented dough, whether in the form of wild yeast starter or commercially yeasted biga, provides both flavor development and acidity to control the enzymes.  When baking 100% whole grain breads, a higher percentage of these acidic pre-ferments is required than in white flours breads because of increased enzyme activity (many of the enzymes are brought into the flour via the bran and germ).  Late enzyme attacks on the starches and proteins during both the fermentation and baking stages can cause the dough to collapse into a gummy substance.

I suppose it could be argued that using a higher than average preferment (especially given the relatively low acidity of the starter) is beneficial for this whole wheat bread for that reason as well as accelerating the process in general.

The desem loaves I've been baking in the last couple of days are some of the best whole wheat loaves I've made so far in terms of both flavor and overall form, although I've never experienced the "real deal" out of my own kitchen, so I'm left guessing if I've done it right.  It really does seem to lend itself to whole wheat.  Although it is just another flour+water+salt bread, it's a shame it seems to have fallen off of the map.  I plan to make this my regular loaf for learning, so I appreciate the input.  It really is eye opening to see that these cold starters can work so well.

 

 

Debra Wink's picture
Debra Wink

I found a few posts (including a post from you in 2009) suggesting that the lengthy authentic desem starter build she describes (10 lb bag of flour, etc) could effectively be replaced by a low hydration and low temperature conversion of an existing starter with frequent enough feeding to avoid acid build up.

Yes, yes, please don't waste 10 # of good grain or flour. I did it that way the first time thinking I could then use the flour to feed the starter, but it wasn't fit for anything after all was said and done. The flour smelled like a damp old dish rag, and that translated to some strong off flavors. In the end, my desem followed the same pattern as any other sourdough, except that it took a lot longer because of the low temperature. I see no benefit to burying in flour except maybe it keeps mold at bay, but there are other ways of preventing that. Converting an established starter is truly the easiest way to go about it.

I think Laurel's bread formula for a new desem starter is 50% of the flour prefermented, and as the starter gets stronger she moves you to 33% or there abouts. But by the looks of your bread, your starter is already in great shape. Reinhart's explanation doesn't make much sense to me, because starch attack is thwarted by acidity, but protein (gluten) breakdown is accelerated by it. That is not what you want. Luckily, desem's management keeps acidity low compared with an ordinary ww sourdough kept at 100% hydration and ambient temperature. And starch attack is generally not a problem in wheat as it can be for rye, because wheat's starch degrading enzymes work in a different temperature range. (See below)

After studying Laurel, I recommend reading Thom Leonard's The Bread Book - A Natural, Whole-Grain Seed-to-Loaf Approach to Real Bread. Thom was working at the Baldwin Hill bakery back when Laurel was there learning the process. He does a beautiful and concise job of explaining why/when to reduce the prefermented flour. We shared some email exchanges back when I was playing with desem, and he helped me quite a bit. That's where my lower rate of prefermented flour came from, so I have to credit that to him. 

All in all, your loaf looks about as good as any desem I've ever seen --- certainly better than the majority of mine. Except for this freak that seems like a unicorn now, if I hadn't had the good sense to take a photo of it to prove it really did happen:

desem baguette

All the stars must have aligned that day :-)

Edited to correct that the difference is gelatinization temperatures of the starches. Starches in rye gelatinize at a lower temperature than that which deactivates the amylase enzymes, giving them about a 10-degree window of opportunity to quickly degrade starches during the baking process. But wheat starches gelatinize at a high enough temperature that the enzymes are deactivated by then. Before gelatinization only the damaged starch absorbs water, making it available to enzymes. Once gelatinized it all becomes vulnerable.

headupinclouds's picture
headupinclouds

my desem followed the same pattern as any other sourdough, except that it took a lot longer because of the low temperature.

That is a notable drawback of working at these temperatures.  Multi stage builds to bring a starter back to health or scale up for a larger bake can takes days!  I was curious about some of your comments on off flavors in one post, which hasn't been my experience.  I can imagine the start from scratch approach being more prone to this.

Reinhart's explanation doesn't make much sense to me, because starch attack is thwarted by acidity, but protein (gluten) breakdown is accelerated by it.

Thanks for another important clarification.  Now I'm curious what other bits of knowledge I've picked up from books (or the internet) are misguided or simply wrong. 

Thom Leonard's The Bread Book - A Natural, Whole-Grain Seed-to-Loaf Approach to Real Bread

Excellent.  I haven't come across that one yet.

Except for this freak that seems like a unicorn now,

That looks like a very light crumb -- uniform and not overly "holey".  A good gateway loaf for those who don't like whole wheat.  That seems like a nice sweet spot to me.

Debra Wink's picture
Debra Wink

The stated motivation for the third and final point is that a larger percentage of preferemented flour results in a faster rise, with less chance for acid build up.

This part is more of a balancing act. True, a larger percentage of prefermented flour provides more yeast to raise the dough faster. But it also means you're starting with more spent flour, more acid, and more bacteria to continue generating acid. So the balance between yeast and bacteria, and their metabolic effects, is important throughout. As well as the proteolytic enzyme content of the flour, the hydration, the temperature, etc. All of these things either contribute to encouraging or discouraging bacterial activity, and/or the rate of breakdown of the gluten network. Low hydration and low temperature slow both bacterial and enzymatic activity. A twofer. But current trends are pushing higher hydrations to open up crumb, which is kind of counter to desem's design. Higher hydration benefits bacteria and enzymes, shifting the balance in the wrong direction. The antidote is decreasing the prefermented flour, starting with less bacteria, acid and spent flour, and letting the salt in the dough slow them down. Bacteria are affected more by the salt than yeast are, so it's another way to take advantage of disparity. But don't feel you need to fix what isn't broken. Let your bread and your taste determine what's right for your flour and your dough.