The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Acetic vs. Lactic Flavor

DanAyo's picture
DanAyo

Acetic vs. Lactic Flavor

My latest endeavor is learning to bake a sourdough bread that heavily favors the Lactic Acid flavor. In an effort to achieve this goal I have baked about 2 dozen loaves back to back and often 5 or so days a week. I’ve come to some conclusions.

For me, it is informative to read that a certain method will produce a particular outcome. But where I learn best is by actually performing the method and then seeing (and in this case tasting) the results. I believe most would agree.

After said testing I know that warm ferments produce Lactic (smooth, creamy, yogurt-like) flavors and cold ferments produce Acetic (sharp, tangy) flavors. And the longer each dough ferments under either warm or cold temperature, the more prominently flavored the bread will taste.

I have also learned that it is possible to use both warm and cold fermentation on the same dough to bring out both spectrums of flavor. 

I last experimented by baking 2 identical loaves. All things being equal EXCEPT one loaf under went a total of 18 hr (counting BF and proofing time) of fermentation @ 77F. The other loaf BF for 16 hr @ 77F and cold proofed for 22 hr in the frig @ 39F. The flavor of the first bread was mild, creamy, and yogurt-like. The second bake was more complicated to describe. It had back tones of the previously described flavors, but in the forefront it tasted tangy and somewhat sharp. From this test I know now that I enjoy the Lactic flavor but not at all the Acetic side. I have the same affinity for cheese. I much prefer mild cheddar instead of the sharp version.

If you are still reading, know that I appreciate your patience. I’ve gone long to set the stage.

Now that I know I want as much Lactic and as little as possible Acetic, how can I maximize this?  My best method thus far is 16 hr BF @ 77F followed by a 79F Proof. The dough will generally tolerate 1.5 hr proof. The length of the BF is limited because the enzymatic action along with the building acid degrades the dough over time. From much testing, it seems the temperature and times are maxed out. Much more (either time or temp) and the dough falls apart, degrades. If I increase the temperature, I’ll have to decrease the time and vice-versa. In upcoming test I may BF for 15hr @ 77F and then proof @ 82 - 84F until properly proofed. I’ve learned so much from dabrownman. I’m excited to give his high temp (82 - 84F) approach. Should I push the proof even higher?

Any thoughts and suggestions are very much appreciated. Thanks for taking the time to read this long drawn out post.

Dan

 

Danni3ll3's picture
Danni3ll3

from your posts so keep it up! 

Question though: What is your percentage of Pre-fermented flour? I am impressed that you are doing 17 hour bulk ferments! Not that I plan to start doing that! I spend enough time as it is with sprouting, milling, sifting, and toasting, not to mention the bulk phase. 

Filomatic's picture
Filomatic

Yes, I'm wondering the same thing.  Did you experiment with different percentages of prefermented flour and times?  I'm really curious to learn how your arrived at that sweet spot.

DanAyo's picture
DanAyo

I made quantum leaps in the sourdough baking when I took Teresa’s Greenway’s online course, “Bake San Francisco Sourdough”. 

$20 well spent. http://www.northwestsourdough.com/

Dan

barryvabeach's picture
barryvabeach

Dan,  according to Debra Wink, to get sour, you want high temps, not low - so I have been trying around 82,  and that has increased the sour for me.  https://brodandtaylor.com/make-sourdough-more-sour/   

DanAyo's picture
DanAyo

Barry, I bet if you check with Debra you’ll learn that cooler temperatures cater to the Acetic Acid Bacteria. The Acetic Acids make for a sharp, tangy flavored bread. But it is also possble to build Acetic and Lactic flavors in the same dough.

Dan

HansB's picture
HansB

As much as I could not get by without my B&T proofer, I have not found their info about sourness to work for me. See below:

DanAyo's picture
DanAyo

Yes, Hans. I completely agree. I don’t find the information you mention correct. For those interested, here is the link in question.

https://brodandtaylor.com/make-sourdough-more-or-less-sour-part-2/

To cloudy the waters more, I think there are 2 basic sours that have very different flavors. The article doesn’t differentiate between the two. My best attempt to describe the two flavors is similar to comparing the difference between sharp cheddar cheese and mild cheddar. BUT, I have no scientific background, only observations.

Dan

DanAyo's picture
DanAyo

I think the question is, do we consider only the Acetic Acid sour? Or is the milder Lactic Acid also considered a sour flavor. At this time I am under the impression that both acids are considered sour. I hope to be corrected if this is not correct.

We all know there are 2 basic acids in any starter. One, Acetic acid produces a sharp, vinegary flavor. The other, Lactic Acid produces a mild yogurt-like flavor. It is my understanding that Acetic Acids become more prominent with low hydration and cool temperatures. And Lactic acids become more prominent with high hydration and warmer temperatures. It is also my understanding that in any given starter, Levain, or Levained bread dough that both types of these acids will be present. We can’t eliminate either one, but we can provide an environment that caters to one over the other. By doing this we can develop very different flavors. We can also mix our techniques (example - warm bulk proof and cold final proof) in order to high light both extremes of each flavor. Dabrownman is famous for this.

After I tasted a Lactic sour bread, and once I learned the above I knew I was off on a new journey. I am many experiments down the road, with many more to go.

Dan

DanAyo's picture
DanAyo

Great question, Danni. I should have included that along with the hydration. I use 2% of the total flour in the Levain. Those dough is mixed to 70% hydration. So about 20g (100% hydration) Levain for an 800g loaf.

I may lower the hydration. That should give the dough a little more tolerance for time and warmth.

Would you believe that the acid load of such a minuscule amount of starter has a noticeable affect on the dough. I’ve experimented with a sweet (non acidic) and an acid starter on the same bake. One dough stayed intact the other degraded because of the additional acid.

Dan

Filomatic's picture
Filomatic

So then how do you prepare your starter for model bread?

DanAyo's picture
DanAyo

Filo, can you rephrase yet question ? I don’t understand it.

Filomatic's picture
Filomatic

I understand you to mean that you used a less acidic starter for this long fermentation because an acidic one broke the dough down. I’m asking how you prepared the starter that resulted in what you say is your favorite bread from these tests.

DanAyo's picture
DanAyo

I used 2 different starters. One I made and 1 I got from a friend. I assume either the LAB was different or the concentration of LAB where different. The starter I got from my friend smelled and tasted “sweet”, very non- acidic. Mine is more acidic.

Here are some images from the test I ran. BTW, this test also compared Morbread flour to KA bread flour.

The image below shows 2 breads that were baked using the same exact procedures as the 2 breads below. The fermentations are are precisely controlled in a proofer and the dough temperatures are monitored. The top 2 breads were mixed with the “sweet” starter and the bottom 2 were mixed with the acidic starter. Even at such a minuscule amount of Levain (2% TFL flour pre-fermented) the results are extreme. The acid load in the last bake caused the dough to degrade. It wouldn’t hold a shape.

BTW, Morbread is outstanding for this bake. I did side by side comparisons to test flours. Morbread was the standout winner by a long shot. I tested KA BF, KA AP, KA Sir Lancelot, Bob’ Red Mill Artisan against Morbread. I even tried supplementing the KA BF with Vital Wheat Gluten and it didn’t compare. I plan to test Central Milling against Morbread in the future. For extended warm fermentation the flour makes the difference between success and failure.

Here is what failure looks like. Dough degraded to slop. Gluten matrix damaged, won’t hold a shape.

Dan

 

DanAyo's picture
DanAyo

If you wanted to make your Acetic starter less acid, you could increase the amount of flour. Feed more heavily. Also, I think a temperature of 70 - 76F would provide an environment conducive to yeast and not so much acid. Try to refresh your starter before it completely falls. Debra taught me the ideal time to feed your starter is right after it starts to fall. If you wait too long the acids will begin multiplying and the yeast will start to decrease.

I’m no expert. Hopefully others more knowledgeable will enlighten us all. I love learning...

Dan

Filomatic's picture
Filomatic

This comports with my understanding. Great work and thanks for sharing your experiments. I’ve been wanting to try a “micro levain” recipe, and this is very instructive. Have you tried this with freshly ground flour?  What’s available here in the Bay Area mostly comes from Guisto’s, and it’s fabulous. 

DanAyo's picture
DanAyo

I’ve experimented with many starter feedings. But for me a good all purpose flour works best. Whole grains make a starter starter grow very fast. I’m my case, too fast. I leave my starter out or in a proofer and I choose to feed twice a day. I can’t get whole wheat to cycle from feed to recede in 12 hours. It grows too fast.  It will start to recede in about 8 maybe 9 hours.  If a starter stays in recession for 3 - 4 hours before feeding, it will quickly become acedic and the yeast will start to decline. So, AP flour works best for me.

HTH

Dan

leslieruf's picture
leslieruf

to do this without a proofer? I don’t have one and just go with ambient temperature.

Leslie

BreadBabies's picture
BreadBabies

What if instead of doing a small innoculation in your bread, you do a large innoculation. But the innoculation itself has been fermented (for a long time) at your lactic acid producing temperature. Go ahead and let it degrade (pre-ferments are often degraded). Then experiment with mixing different amounts of that into your bread (probably add some diastatic malt to ensure browning). Perhaps the gluten from the non-fermented portion of the dough will behave differently than merely adding vital wheat gluten to a dough where the entire dough is degraded.

Again, just thinking out loud. I have no idea if it will work.

DanAyo's picture
DanAyo

Let’s think out loud together ;-)

Initially I’m more inclined to think less Levain. Here’s my thinking. Less Levain will increase the bulk fermentation time. I’m operating under the assumption that the longer a dough ferments, the more intense the flavor. And the initial reduction in acid load brought in would/might benefit the dough over the extended fermentation time. BUT, here is my concern. It seems the dough is degraded by both the enzymatic action of the water and flour mix and also the acids from the Levain. Will the enzymatic action damage the dough too much because of the extended fermentation time? Will the smaller acid load, given more time (now that the BF has been extended), produce even more acid? And will the acid increase towards the end of the ferment degrade the dough during the prolonged time?

On the other hand, your suggestion, seems to work exactly opposite. Increasing the Levain would reduce the fermentation time. It would also introduce more acid from the very start of the BF. BUT would the reduced BF degrade the dough less as a result of reduced enzymatic action?

Theory will only take us so far. It seems yet another experiment is born...

This may be of interest to some. In order to get as accurate a testing as possible I built a separator that fits inside the dough tub. Originally I opted to BF both doughs in separate containers inside the same proofer. The problem with this is the doughs do not ferment at the same temperatures. “A divider was born”.

 

To my surprise it worked the first try. It is closely fitted and as each dough expands the divider is held firmly in place. During testing the dough temps are periodically check. They are identical.

Testing is time consuming and requires persistence. But, as almost stated in the Bible , “if you continue in your testing, you shall know the truth” :D

Thanks for your suggestions.

Dan

Oh, the addition of diastatic malt. When it comes to browning, these loaves have no problem. The starches that are damaged during fermentation make the bread subject to burning easily. I reduce the temperature of the oven to 465F and often have to cover the tops with foil to prevent over browning. The diastatic malt might feed the microbes, but that hasn’t been an issue so far. Because of the low inoculation, they happily multiply throughout the duration of fermentation.

BreadBabies's picture
BreadBabies

First of all...you are a maniac....in the best kind of way. 

I realize that what I am suggesting is sort of the opposite. But my thinking is that by using the levain as your primary source of lactic acid rather than a long ferment you aren't limiting yourself on how long you can ferment your levain. Go ahead a ferment it a really long time to build up the lactic acid because you will be adding it to dough that still has integrity and NOT fermenting the final dough as long as you have been. But if you end up using a large amount of that in your final dough then you would probably need the diastatic malt. Just trying to find a way you can extend your fermentation...which in this suggestion is to ferment the levain longer... not the final dough. 

Of course there are limits beyond gluten degradation and you would have to play with those too. 

BreadBabies's picture
BreadBabies

thinking about this makes me want to try it ... but busted leg won't allow it. 

And to be clear... I was only suggesting the malt in the event you were to use a high amount of pre-digested flour... not with your low inoculation. I have Reinhart's epoxy method in mind. Some dough for your flavor...some for the integrity...something to make it rise. Mix it all up. (I just fixed a bunch of typos.  Writing on a phone.)

rpooley's picture
rpooley

I only started making my own naturally leavened bread when I learned how to promote lactic over acetic acid production.  I don't like the sour acetic acid flavor at all but I love the keeping qualities of these types of bread.  It can last a week beautifully.

I keep my starter on the counter and my kitchen is about 70-74 degrees.  I keep about 1/4 cup at a time, roughly 50/50 flour water mix.  Once or twice a week, I stir in a spoonful or 2 of flour and enough water to keep loose since I read that wetter starters also favor lactic acid production.  When I want to bake, I eyeball the flour and water (I need 100g for my recipe, 50g flour, 50g water) and add it to the starter container and let it sit for 8-12 hours.  Bulk fermentation is room temp about 4-5 hours, shape and into the fridge overnight.  For whatever reason, this time in the fridge still doesn't give it a sour/acetic acid flavor.  I'm really happy with my results.

 

 

Trevor J Wilson's picture
Trevor J Wilson

Hey Dan, this may not be exactly what you had in mind, but if you're looking to experiment with flavor then it might be worth a shot. This is the short short version of the article I'm working on for my blog that touches quite heavily on this subject. You'll need a stiffer dough, maybe 65% hydration. It doesn't work well with wetter dough. Here's the basic idea . . .

Make your dough with around 10% starter by total dough weight. Keep the temps warm -- high 70's low 80's. For your first try you'll want to use an all-white dough or mostly white dough so that you can taste the flavors of fermentation with a neutral background. You're aiming for around 10-12 hours of fermentation. This should be an active fermentation -- not the long slow overnight rise you've been using lately. 

Your basic schedule should consist of around 4-6 hours bulk (the dough should double or even triple in volume). Then punch down the dough and heavily degas with folds, and let it go another 2-3 hours or so until it's doubled again. Punch down and degas again then preshape. Let rest for 30-60 minutes. It should proof enough so that it requires another degassing before shaping. Then degas and shape. Then another 1-3 hours for the final proof and then bake.

No retarding whatsoever.

If all goes according to plan, the frequent punch downs and degassing will build tremendous strength in the stiff dough, and create an "inflated" dough that will rise high and grow to a massive volume. You'll be surprised how much proof this dough can handle during the final rise, so don't rush to put it into the oven.

This is not an "open crumb" bread. The crumb will be fine and even. But it will also be super soft and fluffy, more like the crumb of a light yeasted loaf. Very kid friendly, especially if you bake it at a lower temperature and to a lighter color.

But it's the flavor that you'll be interested in. The long, active and warm fermentation brings out a ton of flavor -- even in a white bread. The stiffer dough encourages acetic flavors, but the warm fermentation encourages lactic. And there will be plenty of yeast flavors as well for additional complexity. It's a very nice balance, there shouldn't be any of that harsh acidic flavor that you don't want. 

If your starter is healthy, then the dough will not degrade so long as you're using a good all-purpose or bread flour (I prefer bread flour with this method, but I've done it plenty of times with all-purpose as well). It's a long fermentation, but the stiff dough can handle the acid, and because you are frequently degassing the dough it does not overproof as would a similarly long fermented dough without the degassing and strength building that you perform here.

It's a different bread style altogether -- better for sandwiches and toast -- but it may provide the kind of flavor you are looking for. When I publish my article, there will be plenty more info and detail included to better explain the why's and how's. Consider this a preview. 

Cheers!

Trevor

leslieruf's picture
leslieruf

Thank you Dan for the thread, Trevor for your input. As always, we are learning so much. and there is always more to learn 😊

Leslie

DanAyo's picture
DanAyo

I plan to make this a future test bake. To be clear, when you say 10% of the TDW, this is my understanding. You use a 100% hydrated Levain. So, if the TDW was 1000g you would use 100g of 100% hydrated Levain. I read your book twice, but I want to make sure I get the Levain weight correct.

Please remember to email me when to post this bake to your blog.

Trevor, I think I speak for many on this forum when I say THANKS so much! We appreciate your kind spirit and your willingness to openly share what you’ve learned. You are a gentleman and a scholar.

Dan

Trevor J Wilson's picture
Trevor J Wilson

If you make 1000g of dough then starter would be 100g. For my article I use a 100% hydration starter, but I actually prefer this recipe with a stiff starter -- 50% or 60% hydration. Currently I've been keeping a 60% hydration starter and converting to a 100% hydration leaven for most of my bakes. I tend to use the 100% hydro starter for my blog recipes because that's what most folks are using so it limits confusion, but throughout the bulk of my baking career I've generally favored stiff starters, both for flavor reasons and ease of maintenance. Still, I switch it up fairly often. 

Trevor

DanAyo's picture
DanAyo

Would it be best to use a 60% Levain or build a 100% Levain from a 60% starter? I also keep a 60% starter.

Dan

Trevor J Wilson's picture
Trevor J Wilson

My personal preference for this style of bread is to use mature, ideally stiff starter. So when I mix this up in the morning I just use straight starter, usually around 12 hours old. I prefer the flavor that a 60% hydration starter brings to this loaf over the flavor that a 100% brings, but it's subtle and both are good. 

Trevor

DanAyo's picture
DanAyo

I’d love to learn how to handle starter/Levain timing. Say I want to start the mix at 2PM. My starter is fed each day at 7AM and 7PM. And I don’t want to start my feed @ 2AM, but it requires 12 hr (normal ferment time) in order to be ready.

How do you handle this?

I’m thinking that my normal feed is 1:3:5. In order to speed the ferment time I might go something like (2.5):3:5. So instead of 20% starter to flour, I’d mix 50% starter to flour.

Am I on the right track?

Danny

Trevor J Wilson's picture
Trevor J Wilson

Increasing the seed in your starter can certainly speed up the fermentation -- so it may very well be ready for a 2PM mix time. But then what? Do you refresh the starter at 2PM as well, again with a higher seed ratio so that it will be ready by 7PM for its usual feed? Or do you just let it continue to ferment and potentially over acidify?

I suppose you could build a separate leaven with the larger inoculation for your dough along with your 7AM refreshment, but that doubles the morning's work (if that's a concern at all). That way your starter can be left to continue at its normal pace while the leaven moves quicker for the earlier mix. (I am curious if you intend to bake this loaf at midnight or 2AM since it's a 10-12 hour fermentation without retardation, which is sort of the point).

Honestly, in your situation what I normally do is just steal from the starter at 2PM for the mix. It may not be a 12 hour mature starter, but at 7 hours it should be well-risen and strong enough to leaven a dough. Make a little extra if you need to so there's enough left over for the 7PM refreshment. To make up for the younger starter I would probably use a larger amount (maybe 12% to 15% by dough weight) or slightly raise the proofing temp (or some combo of the two). Trial and error teaches best here.

Not to pick on you (well, not to pick on you too much), but the problem in your thinking shows itself when you say of the starter, "it requires 12 hr . . . to be ready." It doesn't. Though a 12 hour starter might provide a slightly better flavor (in my opinion, but maybe not in yours), a 7 hour starter should do the job just fine. Flavor differences are subtle. These things don't have to be perfect. Bread baking should be a flexible process that we comfortably fit in with our daily routine, not something that we set our clocks to and bend over backwards for. Far better to simplify the process than to complicate it. When in doubt, simply ask yourself, "What's easiest?"

Cheers!

Trevor

DanAyo's picture
DanAyo

What I was thinking is to build the Levain for the 2PM dough mix at the same time I did my morning refresh of the starter. In this case I would have a starter and a Levain going at the same time. I thought that the higher percentage of starter in the Levian mix would cause it to mature in less time.

The reason I shoot for early afternoon for the dough mix is because the bake I am presently working with has about a 16 hr bulk proof. So if I start at 2PM, I’ll be ready to preshape around 6AM.

When I mention that the starter would mature in 12 hr. I am thinking that at 12 hr. the yeast (not the flavor) would be maximized in that time. It takes my starter 12 hr to go from feed to just beginning to recede.

I almost always opt for the best method. But, if mixing more starter at 7AM and removing what I need from the starter @ 2PM is equally good, then that sounds good and a slight bit easier.

You are very gentle in any criticism that you offered on this site. If I need “picking on” please do so. I am very interested in learning :D

Dan

DanAyo's picture
DanAyo

It’s 7AM and time to feed my starter. I know that a feed of 1:3:5 @ 76F will need to be re-fed in 12 hr. But I would like to use a Levain @ 2PM and I want it to be mature. I fed it 2.5 starter + 3 water + 5 flour and at 2PM it was perfectly ready.

Increasing the percentage of starter shortened the time to maturity. This is obvious. But sometimes the obvious is not considered.

Dan

DesigningWoman's picture
DesigningWoman

That is very clever!

 

DanAyo's picture
DanAyo

Isn’t it great when you try a new idea and it works! Both starters fed using the same seed culture @ 7AM. Image taken @ 2PM.

Glass on left fed 5:15:25. Glass on right fed 12.5:15:25.

Danny

leslieruf's picture
leslieruf

so my fingers are crossed that I have understood this. I don’t have a proofer but my microwave is keeping temperatures around 80°F.

Baking later today is the plain 🤞🏽😊

Leslie

jbentson's picture
jbentson

Dan I believe it is Acetic acid not Acedic acid

DanAyo's picture
DanAyo

I’ll try to remember the correct spelling. But, I have to admit, for me changing old habits can be a challenge. Thanks for the heads up. I’ll do my best to communicate properly.

Right now I’m saying Acetic, Acetic, Acetic... :D

Dan

Lechem's picture
Lechem

But I'll have to confirm with him first something along the lines of amount of starter to flavour. 

A small amount of liquid starter but a larger percentage of a low hydration starter to maximize the flavour. 

Just dropped him a message and I'm sure he'll look into this discussion. 

DanAyo's picture
DanAyo

I’m interested to learn more about low/high hydration as it relates to flavor.

I think I’ll start the post documenting the next test now, even though the s it not finished.

Dan

doughooker's picture
doughooker

Frankly, I don't bother with these biochemistry experiments any more :-)

I've taken the bull by the horns and add the acids directly to the dough and have never looked back. The bread is divine. No starter and it proofs in 2 hours. Details in my blog:

http://www.thefreshloaf.com/node/49375/san-franciscostyle-sour-bread

Doc.Dough's picture
Doc.Dough

In every experiment I have run, the trajectory of LAB growth is to multiply faster than the yeast until the pH gets to <5.0 where the yeast and LAB growth rates cross over.  Below pH 5, the LAB continues to replicate all the way down to around pH 3.8 at which point the total population of LAB stabilizes while the yeast population continues its exponential growth until the glucose in the dough is exhausted.  During this period at and below pH 3.8 the LAB continue to produce acid at a rate that seems to be modulated by the concentraiton of usable sugars so that acid production slows down as the yeast growth rate (CO2 production rate) continues to decline.  I have TTA data that confirms acid production in a very high hydration (250%) levain for over 30 hrs at room temperature though I cannot distinguish the relative amounts of acetic and lactic acids present.

The claim is made above that at higher temperatures the LAB are inclined to produce acetic acid while at lower temperatures LAB tend to produce more lactic acid.  The only lever I know of to adjust acetic:lactic ratio is the amount of fructose in the mix. So I am curious about the underlying biochemistry by which temperature controls the specific acid production rate.

To suppress the yeast growth rate so that acid production continues for extended periods, it seems necessary to reduce the population of yeast relative to LAB which DBM teaches us can be achieved with long periods of starter refrigeration. So whether you want large amounts of lactic or acetic acid you have to start with just enough (but not too much) yeast.

Since the vapor pressure of acetic acid is so much higher than that of lactic acid, the only acid you can actually smell in a sourdough is the acetic component, while the lactic acid has a distinctive (after)taste.

I am curious how the relative amounts of lactic and acetic acid were determined in the experiments described above.

Additionally, the loss of structure in an old dough is likely not caused directly by acid, but by protease activity which is increased at low pH rather than by high acid concentration (TTA), so I am interested in the rationale for attributing the loss of gluten strength/dough structure to acid alone.

DanAyo's picture
DanAyo

Doc Dough - You wrote, “Additionally, the loss of structure in an old dough is likely not caused directly by acid, but by protease activity which is increased at low pH rather than by high acid concentration (TTA), so I am interested in the rationale for attributing the loss of gluten strength/dough structure to acid alone.”

I was under the impression that higher acidity caused the dough to weaken at a faster rate. I say this because in a comparative test the dough with the Levain with more acid degraded much more over the same length of time. But if I understand you correctly it is not the increased acidity, but that the lower PH creates an environment that facilitates more/higher protease activity. So, it is actually that protease activity and not the acid that is responsible for the premature breakdown of the dough. Do I understand that correctly? I appreciate the clarification.

Dan

I decided to lookup information, in order to learn more about this. And I must say, after trying to read scientific papers on the subject how much I appreciate your simplified answer. 

derived from gluten (e.g. gliadin), which are involved in coeliac disease and they are present in wheat-baked foods. During endoluminal proteolytic digestion, prolamins of wheat (a-, b-, c- and x-gliadin subgroups), rye (e.g. secalin) or barley (e.g. hordein) release a family of proline- and glycine-rich polypeptides causing an inappropriate T-cell- mediated response (Silano and De Vincenzi 1999a). Studies with fragments of a-gliadin clearly indicated that few short sequences very rich in glutamine and proline residues (e.g. P-S-Q-Q and Q-Q-Q-P sequences) are toxic to coeliac patients and they caused an inflammatory response of the small intestinal mucosa. The infusion of the 31–43 fragment of a-gliadin, which contains the sequence Q-Q-Q-P, directly into the jejunum of treated coeliac patients was shown to be toxic by mucosal biopsies (Marsh et al. 1995).

This study deals with the proteolytic system of Lact. plantarum strains (CRL 759 and CRL 778) isolated from sourdough and their ability to hydrolyse the toxic 31–43 a- gliadin fragment.”

This kind of information is waaaay above me. It causes brain-pain to read these type of things, much less comprehend it :D

 

Doc.Dough's picture
Doc.Dough

http://www.aaccnet.org/publications/cc/backissues/1978/Documents/chem55_461.pdf

This paper contains a lot of useful information. 

First, it quantifies the acids in commercial sourdough at various points in the process.

Second, it assesses the ratio of lactic to acetic acid.

Third, it points out that the pH that brings the protease out to play (3 to 4) is also the pH where the LAB will put your dough when the LAB population density stabilizes.

Fourth, it addresses the inhibition of protease activity through the addition of salt, though while 3% salt is a little high for most breads, it turns out that as you increase the TTA, you probably want to increase the salt as well to balance it out.  If you examine Hamelman's formulas for breads with increasing amounts of whole grain (which turns out to also increase the TTA in general), you find that he increases the amount of salt as well.

I am curious about how you measure "acidity". Generally TTA is taken as the measure of acidity and it correlates with the perceived level of "sourness" that a loaf delivers in the mouth.  Protease activity on the other hand responds to pH which is only indirectly related to TTA.  You can have a dough with a pH of 3.8 that contains only a small amount of acid as measured by TTA while another sample (fermented longer) will have nearly the same pH but a much higher TTA and deliver a much more sour sensation.

I don't know the exact source of the protease enzymes but it could be that your two different flours either innately contain or develop as a result of biochemical activity different levels of protease activity.

 

HansB's picture
HansB

I have found that this is accurate in my SD baking. Keeping my starter cooler and cold fermenting produces much more acetic, sour flavor for me.

 

Bacterial Fermentation

 

Bacteria are primitive one-celled organisms. The types of bacteria common in bread dough consume the same simple sugars used by yeast cells. The primary by-products of bacteria in dough fermentation, though, are two types of organic acids: lactic acid and acetic acid. Lactic acid is also found naturally in milk and in concentrated form it produces the tangy flavor we find in yogurt. Acetic acid is found in all varieties of vinegar and is more sour than lactic acid.

 

ORGANIC ACIDS PROVIDE STRENGTH AND FLAVOR

 

The types of bacteria that produce these acids can thrive in temperatures of 50-90F and are collectively referred to as lactic bacteria. As bakers, we are concerned with two types of LAB, homofermentative and heterofermentative.

 

These names may seem hard to pronounce and even harder to remember, but it is important to identify them and explain a bit about their behavior. Yeast must be regulated to control how fast the dough rises, but the bacteria primarily determine how well your dough will mature and how the bread will taste. 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.

 

This is, perhaps, the one concept in artisan style baking that escapes bakers who look for easy, time saving ways to make bread. Unfortunately, bacterial fermentation almost always proceeds more slowly than yeast fermentation, much more slowly. Scientist have successfully isolated strains of the yeast saccharomyces cerevisiae that can speed carbon dioxide production considerably. Lactic bacteria have so far been much less cooperative; the bacteria in bread dough we make today probably aren’t different from those present in the times of Moses.

 

HOMOFERMENTATIVE BACTERIA

 

Homofermentative bacteria prefer environments that are wet and moderately warm, perhaps 70-95F. Their chief by-product during fermentation is lactic acid which is fairly mild in it's sourness compared to the sharper acids contained in lemon juice or  vinegar. Homofermentative bacteria can survive in somewhat drier conditions and within other temperature ranges but they do better in the warmer range.

 

HETEROFERMENTATIVE BACTERIA

 

Heterofermentative Bacteria do better in somewhat drier and cooler environments, they prefer temperatures of about 50-65F. They produce both lactic acid and acetic acid as by-products as well as a small amount of CO2. Acetic acid is also found commonly in vinegar and it’s flavor is much sharper that that of lactic acid.Heterofermmentative bacteria can survive in some numbers as different temperatures than specified and in wetter environments, but drier and cooler situations favor their reproduction and their ability to ferment bread dough.

 

 

Daniel T. DiMuzio, Bread Baking.

 

bikeprof's picture
bikeprof

I'm not seeing it...so, once again, here is an important reference on the topic from Wink and the TFL crew:

http://www.thefreshloaf.com//node/10375/lactic-acid-fermentation-sourdough

 

I'll be taking Debbie's Science Behind Sourdough class next weekend in Jersey City, and am rereading the above thread in preparation...should be fun...

 

bikeprof's picture
bikeprof

Here is just one snippet from the link I posted:

"Acidification is also influenced by hydration and temperature. Contrary to popular belief, all three groups of sourdough lactobacilli prefer wetter doughs a bit on the warm side, many growing fastest at about 90ºF or a little higher. For the homofermentive species producing only lactic acid, increasing activity by raising the hydration and/or temperature will increase acid production. Decreasing activity by reducing hydration or by retarding will slow production. There is a direct relationship between activity and lactic acid. During heterofermentation, for each molecule of glucose consumed, one lactic acid is produced, along with one carbon dioxide (if a hexose is fermented), and either one ethanol or one acetic acid. But under wetter, warmer conditions, where sugars are metabolized more rapidly, the tendency is toward lactic acid and alcohol production in obligate heterofermenters, and all lactic acid (homofermentation) in the facultative heterofermenters. Lactic acid production is directly related to activity during heterofermentation just as in homofermentation, even if only half the rate.

At lower hydrations and temperatures (lower activity), more acetic acid is produced, but not because of temperature per se. Acetic acid production is influenced indirectly by temperature, in that it affects the kinds of sugars available. The fructose that drives acetic acid production, is liberated from fructose-containing substances in flour, largely through the enzyme activity of yeast. And, because lower temperatures are more suited to yeast growth than higher, more fructose is made available to the bacteria at lower temperatures. At the same time, the bacteria are growing and using maltose more slowly, so the demand for co-substrates goes down as the fructose supply goes up. The ratio of acetic acid to ethanol and lactic acid goes up, because a higher percentage of the maltose is being co-metabolized with fructose. Reducing hydration has a similar effect of slowing the bacteria more than yeast, which I believe is the real basis for increased acetic acid production in lean breads made with refined flours."