The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Tip - Lactic vs Acetic Smell Test

DanAyo's picture
DanAyo

Tip - Lactic vs Acetic Smell Test

There is a tremendous interest in sourdough, largely in part due to the distinct flavors produced by Lactic and Acetic acids. There are a number of current descriptions attempting to describe each flavor and/or smell. Example; Acetic = vinegar, Lactic = yogurt. I often use Acetic = sharp cheddar cheese, Lactic = mild cheddar.

I think I’ve come across a very simple way to observe the obvious differences.

  • Start with an active starter
  • Mix a 60% starter
  • Mix a 100% starter
  • Ferment both starters in the same location
  • Make sure they mature at or near the same time  * See note below
  • With the covers removed from each of the mature starters, cup your hands over the opening (to seal the gasses in) and place your nose between your hands.
  • Smell the differences and compare the 2 starters
  • Tastes a minute amount (Don’t be chicken :D)

If you do the comparative test, please report your findings. Reading and hearing about something is good, but the sensory test will drive the truth home.

* Starter are unique. In my case the 60% starter was mixed 1:7:12 and the 100% was mixed 1:20:20 for a 12 hour feed cycle @ ~73F. 

Although the test requires a small effort, the results produced should be vivid. The flavors of sourdough vary quite a bit. Not only from mild to pungent, but also from Acetic to Lactic and their combinations. In any starter Lactic Acids will dominate in percentages, but Acetic Acids are potent and their smell is strong.

So, how do you coax the 2 different acids? Cool and dry = Acetic, warm and wet = Lactic.

Danny

dmsnyder's picture
dmsnyder

Whether a single feeding is enough to create dramatic differences.

Along with most others here, I have long advocated easy, one step conversion between liquid and firm starters, according to the recipe used and acid balance desired. The problem is, I have been disappointed more often than not. The bread is good, but doesn't really have the flavor profile I was hoping for.

I'm beginning to wonder if one needs to maintain a starter over some longer period of time and with a consistent feeding schedule to achieve a reliably predictable balance of flavors. I know that the folks at the SFBI are meticulous in keeping their liquid starter on a 12 hour feeding schedule and feeding it with a consistent mix of AP and rye flours.

So, I am starting an experiment. I am mixing a 50% hydration starter fed with a AP/WW/Rye flour mix. I will feed it on a regular schedule - I'm thinking every other day . I will refrigerate it if life throws off my schedule. Then, in a week or two, I will build it up and make bread. My goal is a more sour bread. 

BTW, I have a loaf cooling now that was leavened with a starter that started firm and was fed twice at 50% hydration before mixing in a final dough. It was retarded for 17 hours. It has a "twin" that I will retard for 20 or 22 hours.

I look forward to reading about your experimental results.

David

DanAyo's picture
DanAyo

David, I wished Doc lived next door. Maybe we could get him to ascertain the TTA in the single cycle hydration change. I’ve tried PH strips, but don’t have much confidence in them.

Last night I wanted to prepare a 100% starter. So, I mixed it up using a 1-20 ratio of starter to flour in order to get the feed cycle to last 12 hours. I continued to refresh my 60% starter. It is never refrigerated and is feed every 12 hours. In the morning after 12 hours had past I smelled and compared both starters. The smell was completely different between the two. The 60% starter, as usual, smelled what I call “sweet” (not acidic). As expected the 100% starter was extremely pungent. It brought a giant smile to my face :-) By the way - the 100% starter appeared to be timed well for the 12 hr feed. It appears that it achieved max rise and just beginning to recede, but not much.

I do expect and hope the acids continue to increase with continued feedings, but as pungent as it smells already, I’m not sure.

Please give this a try and let us know your findings.

Danny

DanAyo's picture
DanAyo

In writing the above post, a thought came to mind that doesn’t fit my rationale. I believe Acetic = cool and dry, Lactic = warm and wet. And Acetic is sharp (vinegar and Lactic is smooth yogurt). If that is correct, how come the 100% (warm and wet) starter smelled so strong and sharp? It wasn‘t near as strong as ammonia, but it definitely was strong and sharp. I would expect that odor from Acetic Acids.

I would like to understand this.

Danny

 

David R's picture
David R

I haven't smelled lactic acid on its own, ever. Have you?

(Acetic acid is easy, it's vinegar.)

DanAyo's picture
DanAyo

DavidR makes a good point, Lactic acids don’t have strong odors. Why did the starter smell so pungent (healthy sour)? The starter lives on the counter and was kept warm (mid 70s) and wet.

Dan

”those that seek the truth, must willingly accept their errors”
This stuff is hard. And there is no end to learning and discovery.

mikedilger's picture
mikedilger

... at 41C, the dough smelled very very good, very San Franciscy.  I mentally labelled that smell as Lactic acid, but I really have no idea.  Unfortunately the dough didn't work well otherwise, and the smell did not carry through into the final flavor at all.

I'm not convinced that temperature or hydration are huge determinants of lactic vs acetic.  I think type of flour (refined white flour vs anything else) and starter microorganism equilibrium (has the starter been on refined white flour only?) are bigger factors. But this is just a theory. Heterofermentive LAB use 5-carbon sugars (ribulose-5-phosphate, xylulose-5-phosphate, through transketolase) that other LAB don't use, and so if these sugars are available, those heterofermentive LAB will persist in number. And while they are there, they will make their own 5-carbon sugars (from glucose-6-phosphate through 6-phosphate-gluconate via 6-phosphogluconate dehydrogenase). All of these pathways end up making either acetic acid or ethanol. If the food doesn't have 5-carbon sugars, maybe (just maybe) those heterofermentive LAB will be outcompeted by the other LAB that don't waste machinery on handing sugars that are not significantly present. Then all the glucose-6-phosphate can go down the other homofermentive path and end up as lactic acid.

 

In practice, pure white flour starters smell different to me.  And I've always associated that smell with lactic acid.

mikedilger's picture
mikedilger

... L.sf. doesn't feed on 5-carbon sugars at all so it won't diminish. It is obligately heterofermentive so it will always produce acetic acid, but it produces more lactic in a ratio of 4.6 to 1, which is nicely weighted towards lactic.

Here are the relevant metabolic pathways. Sorry for the poorly organised chart (still trying to get graphviz to lay it out better):

Metabolic Pathways

syros's picture
syros

Just a personal observation - you guys are way over my head. 

I just made a 60% starter to make a recipe that dmsynder gave for the San Francisco Style SD from Mike Giraudo. Because my starters are usually 100% hydration, this was a challenge for me. After a couple of feeds, I left my stiff starter in the oven with the light on overnight which was probably a mistake.

It was warm when I took it out, and I could see that it had domed and was receding. When I took the lid off, the pungent smell was strong! I let it air out a bit and took the plunge to make the bread with it. I have posted the photos of the bread (not yet cut into) on the blog section. All to say, my 100% starters only get that strong smell if they have been in the fridge for a week or so. 

It will be interesting to see how this bread looks when I cut into it and what it tastes like. It was bulk fermented 8 hours at room temp, and cold retarded for 12 hours then baked.

I'm sure nothing I've said has contributed anything here, but I was just so surprised at how pungent the stiff starter smelled - which was probably because the temps got too high. I won't do that again!

DanAyo's picture
DanAyo

UPDATE

12 hr after initial test - It is 12 hours since I performed the starter smell test. When feeding time came tonight the starter no longer manifested the pungent, sour smell. I think this is because the room temperature was considerably cooler and the starter didn’t mature. I placed the starter outside since it will be colder there. My hope is that the cooler temps will retard the maturity of the starter until tomorrow morning. Key Takeaway - for optimum sour the starter should be fully mature.

24 hr after initial test - This morning the starter smelled slightly pungent. The starter temp was 68F. I decided to place the starter in the proofer and raise the temp for an hour. The temp rose to 88F and the smell was much stronger.

Question - Is it probable that a very warm starter smells much more pungent because the heats causes the mixture to become less viscous, allowing more gas to escape?

Why would a wet and warm starter smell so strongly sharp, when the consensus seems to be that lactic acids don’t produce strong smelling vapors?

Dan

 

dabrownman's picture
dabrownman

in warmer temperatures is that warmth means molecules move faster when they are cold and those that are volatile,  become more so.  So a warm stored starter should smell much more pungent than a cold one for two reasons, the wee beasties have been working harder and the off gassing of the smell is more abundant.  Makes sense to me  for sure.

dabrownman's picture
dabrownman

First of it isn't just hydration that promotes acetic acid production it is also low temperature.  When I was developing the NMNF Whold Rye NMNF starter that lead to the retarded, whole gran, bran levain to get the LAB to yeast ration higher  to make more acid in general and to get the LAB to make acetic acid. I will never for =get what Debra Wink told me.  It wasn't so much the low temperature and low hydration that would do the trick but the whole grains and very long time that would do it.  Since the temperature was so low, and things happened so slowly,  it would take a very very long time, weeks, for the culture to really get where I wanted it

Time and whole grains are way more important than hydration and temperature from my experience although all are required.

David R's picture
David R

Yeasts reproduce quite quickly, but maybe their life cycle length isn't the primary factor.

Obviously, if you change your starter feeding routine, and then - only five minutes after the new feeding has been done for the first time - you make a batch of dough, that dough is working with the old starter.

One indicator is that a new feeding routine reaches equilibrium, which I would define for this purpose as "the starter's response to the new feedings has stabilized and is predictably the same each time". (Which also means, from the microbes' point of view, that the starter's keeper is stabilized and responding predictably. 🙂)

But maybe more time is needed after an equilibrium is reached, for new developments to take place?

doughooker's picture
doughooker

According to what I've read, the Larraburu sponge was made from clear flour, which is less refined than white flour.

mikedilger's picture
mikedilger

Well there goes another theory.  This shit is hard.

doughooker's picture
doughooker

"This shit is hard."

Courage!

doughooker's picture
doughooker

Could we have specific times and temperatures please, in addition to describing the smell?

We haven't reached a definite conclusion about Larraburu's 4-hour, 105 F proof.

DanAyo's picture
DanAyo

Chris, times and temps. I know 12 hours and I think 76F. The starter was originally mixed with no test or experiment in mind. It was born when I smelled the huge difference between the 60 & 100% starters.

As far as the 105F for 4 hr, that was a bust for me. I’ve attempted that 3 or 4 times and the results were always dismal. I don’t eat bad bread, so the birds got to feast :D

David R's picture
David R

Regarding Larraburu specifically:

I propose, for your entertainment only, two thoughts: first, that the originators of Larraburu's process believed that they knew why it worked, and second, that they were vastly mistaken in that belief. 😁

dabrownman's picture
dabrownman

'real' formula for sure because many of us ate that fine bread at least a couple of times.... even it you just bought it at the airport:-)

David R's picture
David R

Oh, I know for sure that it worked.

I'm saying maybe they didn't know why.

doughooker's picture
doughooker

This is why I'm pursuing the starterless approach. Temperature counts for almost nothing when you don't have a colony of microbes to deal with. There is more consistency/less variation in the finished product. None of this "my bread isn't sour because my kitchen is too cold".

Don't be so quick to lose interest in starterless, Danny. It works just great for me. We need to figure out why it doesn't work for you.

DanAyo's picture
DanAyo

Chris your starterless approach is a novel idea. But IMO it seems more suited for non-sourdough bakers and/or commercial pursuits.

Naturally levained breads are much more healthy and nutritious. I believe I gain much less weight eating breads that have been fermented for extended times. I estimate I eat 5-6 slices of bread a day, every day.  It is more digestible, according to what I read. Then there is staling. What yeasted bread can compare to naturally levained bread. And finally the real deal breaker. Texture and flavor. If you ever develop a yeasted bread that is equal to or better than a good levained bread, I hope you remember me as a good friend. You will be rich beyond measure :D

I champion you for such a unique endeavor. But I am not a worthy candidate for conversion. The value I hope to derive from your endeavor is the possibility of subsidizing my naturally leavened breads with natural acids that you are promoting.

I am very appreciative for your efforts in this area and I thank you for sharing them.

I hope to call you Monday. I plan to have baked the latest version using Doc’s suggestions as you stated them before our call. When will you get a chance to try it?

Danny

David R's picture
David R

It's sourdoughless.

It's "starterless sourdough" in the same way that chess is "painless boxing" - a completely different item, pretending.

If the pretense was completely successful, it would be a spectacular accomplishment, but the pretense isn't really successful at all. Yes it's sour, yes it's dough, but until you can fool a critical expert - for example, to fool Dan into believing that your bread is his own because there's no difference (note: not saying no important differences, but simply 100% no difference) - then it's not a legitimate alternative. This is indeed terribly unfair, but it's also the situation as it stands. Much like when someone is making an accusation, when someone creates an imitation it's up to the imitator to do all the work of proving that the imitation is good, and the imitation is judged by the standards of the listeners, not by the imitator's standards.

doughooker's picture
doughooker

"If the pretense was completely successful, it would be a spectacular accomplishment, but the pretense isn't really successful at all."

It's successful in my kitchen, loaf after loaf.

I can't be in Danny's kitchen to make sure he does everything right. He could be making a mistake that we're not aware of, and he only baked the one loaf. I've baked this many times without a problem and it always has a good flavor.

Why do I get good results and Danny doesn't? That's the mystery that has to be unraveled.

dabrownman's picture
dabrownman

http://www.theartisan.net/flour_descriptions_and_definitions.htm

In wheat bout 2.5% is germ and 14.5% is bran together that is 17 %  Straight flour is what all patent flours are milled from and straight flout is usually 72% of the original.  So the bran, germ and straight flour add up to 89%.  So 11% is sort of missing but maybe not really. - since nothing gets thrown away  Clear flour is what remains after all patent flour is removed from the straight flour supposedly.  Long patent can be 90-95% of the straight flour so lets say that 90% is the long patent flour.  90% of the straight flour would be .9 * 72 or about 65% leaving 7% for the 3 grades of clear flour but maybe nit really.  I'm thinking that the 11% that went missing after the bran, germ and patent were milled out is also considered the darkest grade of clear flour and the other two lighter grades of clear flour are sifted from the 7% after all the patent flour is removed from the straight flour.

This might be why Larraburu crumb was not as open as could have been if the levain was made with clear flour though, if it really was made with clear flour.  It is certainly cheaper than patent flour and bakers are always looking for cheap and good enough to do the job plus the wee beasties would love the clear over patent any day.

Happy baking

mikedilger's picture
mikedilger

I've read multiple sources (e.g. wikipedia, papers, bread books) where 100% extraction means whole grain, and 72% extraction means straight flour.  According to the link you've presented, 100% extraction is straight flour (100% of the 72%) and lower extractions are percent-of-straight-flour rather than percent-of-whole-grain.

This is news to me.  I'll have to be more aware of the different meanings of extraction rate in the future.

As for that missing 11%, it just gets taken out along with the bran and germ because they can't perfectly separate the grain, so some endosperm gets lost just to be sure the bran and germ are completely removed.

 

doughooker's picture
doughooker

What is the difference between "straight" and "whole grain" flour?

mikedilger's picture
mikedilger

Milled Flours

mwilson's picture
mwilson

Flavours are not "produced by" lactic and acetic acids.

Flavour is a result of sensory stimuli that occur in the nose and on the palate.

Flavour = taste + smell.

Smell, or aroma is the more bountiful experience and is due to the presence of volatile flavour compounds which can be detected ortho-nasally or retro-nasally.

In reality lactic acid doesn't really have any aroma whereas acetic acid is volatile and its acidity can be detected nasally.

Flavour descriptors are very much associative and so individual experiences or interpretations will vary. Generalisations can be gleaned, however.

As part of my studies I have tasted diluted acids; acetic (ethanoic), citric, malic, lactic and succinic.

Yes, I would agree likewise as I think most would, acetic acid is "sharper" and lactic more mellow, round, smooth in taste. (see: synaesthesia)

To me the acetic acid smelt very "musty" and tasted horrendously vinegary while lactic was the least offensive.

There are probably hundreds of flavour compounds that are produced as part of sourdough fermentation and the adulteration of dough with just acids is no match to actual fermentation and is why chemically acidified bread doughs have scored poorly in sensory evaluations.