A question about acetic acid in sourdough
Acetic acid is produced when bacteria turns alcohol into vinegar.
There really isn't enough sugar in bread flour to make a lot of alcohol. For beer, under the right conditions with malting grains and boiling them in water, one can extract enough sugar for an average ABV of 3-4%. It also takes a lot of time for the yeasts to convert all the available sugar to alcohol. Higher percentage ABV brews will often have added sugar as well.
Given that we use bread flour which isn't malted. Or if it has added malted flour it's a small percentage and not enough to make a lot of alcohol. It's not in the right medium, liquid, to encourage alcohol production and the bread is made within a day or two and not weeks. How is there enough alcohol for sourdough to have acetic acid? It must be in very small quantities if present at all.
For instance...
18g sugar per litre (1000g) of water = 1% ABV
And I think it doesn't all turn into acetic acid either. I seem to remember 1% ABV will make 0.5% vinegar. Or something like that. Please correct me if i'm wrong.
There is only 5-14g sugar in flour per 1000g flour. That will be a potential of 0.3% ABV to 0.8% ABV. It's not in a medium that encourages alcohol production and there isn't enough time. Even if all gets turned to alcohol only half of that gets turned into vinegar.
So we're talking about minute amounts of 'possible' vinegar.
So is there really any acetic acid in sourdough? And if so, how?
Supposedly various LAB can produce acetic acid as well as lactic acid, depending on the bacteria present and the fermenting conditions. Sourdough isn't just yeast, and those tables and numbers for brewing won't really apply so well.
Here's Debra Winks:
https://www.thefreshloaf.com/node/10375/lactic-acid-fermentation-sourdough#comment-54525
TomP
So thinking about this as someone who has had some experience in making wine it doesn't directly translate to sourdough as far as alcohol and acetic acid?
Acetic acid can be produced other ways not just by bacteria turning alcohol into vinegar.
Thanks for the link.
It is worth noting that acetic acid has very low odor and flavor thresholds:
These low threshold values may help us detect even those minute quantities present in sourdough.
I'm a home brewer and beer with ABVs exceeding 8 % can easily be made with standard brewing yeasts. With wine strains 12% to 13 % or more can be attained. My last porter was above 6 %.
As a brewer you go to some lengths to get a lot of alcohol, don't you? If you brewed beer like sourdough bread is made you wouldn't get those ABV numbers, I'm sure.
I'm not sure what you mean by "some lengths". Brewers just do what sourdough bakers do except it takes a bit longer.
That is manage the fermentation by controlling the temperature of the wort in which the yeasts feed --too high and the yeasts produce unpleasant tasting by-products-- like sourdough bakers control fermentation and baking schedules by feeding schedules and retarding the process sometimes.
Basically we crush and introduce 150 F to 160 F water to the grains to activate the enzymes in the grain and allow them to break the starches into sugars. Then we cool the sugar water to about 64 F to 68 F for ale-style beers and add the yeast. Then we allow the yeast to ferment the sugar water for 10 days or longer. The truth is brewers make sugar water and yeast make beer.
I think you've just illustrated my claim:
- Basically we crush and introduce 150 F to 160 F water to the grains to activate the enzymes in the grain
Bakers rarely do this. Sometimes a soaker is made with bran, grain, or sprouted grain, and sometime it's made with water in that range, sometimes with the intention of sweetening the bread. But it's not common and it's not the essence of bread making.
- The truth is brewers make sugar water and yeast make beer.
Baker's don't make sugar water to make bread.
- Then we allow the yeast to ferment the sugar water for 10 days or longer.
I'm not sure I have made your point. I did admit that brewing beer took longer, but that both brewing and sourdough baking involve controlling the fermentation.
Both involve activating the enzymes; try making bread without liquid. We merely heat our water to a higher temp.
And brewers start earlier in the process; that is obtaining the sugar. If bakers had to process sugar cane or sugar beets into the sugar they needed for the bread it would be a longer process than adding 160 F water to crushed grains.
And oh yeah, you forgot to mention the time it takes to make your starter. When brewers start with grains, the basic process is as described above. You are assuming that you have a starter ready to bake, but that starter took a few days to get ready.
What a fun discussion. You're up for the next round.
Hmmm. For the most part bakers aren't trying to create sugars, and the yeast itself will create most of what it needs from the flour. Yes, there's some amylase in the flour, and yes that breaks help down the starch, but I don't see it as creating a sugary substrate like you do. Bakers see the water as a means to create a gluten network (for wheat flours), and to create a starchy slurry or gel.
Yes, it took a week five years ago. OK, it got refreshed a few hours before use.
For the most part home bakers are content to use water at room temperature or tap temperature. For most recipes there is no need to heat the water at all. Instead of sugar, one main if understated goal for sourdough breads is to improve the flavor with the metabolic products of lactic acid bacteria. If I understand it right, a brewer tries hard *not* to develop LAB.
Not to mention that brewers don't bake their sugary, boozy liquid in a finishing step.
Yes, well, OK, yeast, yeast food, liquid, of course there are some similarities. You can even just buy a sack of sugar, put it into a container with some yeast, and come back some time later and you (might) get a drinkable alcoholic liquid. I wouldn't call that just the same as making bread, though.
Abe does both. Maybe he'd like to chime in here.
That's why I was thinking about acetic acid within a sourdough but from making alcohol perspective as supposed to the LAB being able to also produce acetic acid.
The process of malting and boiling releases all the sugar from the grain to easily be converted to alcohol over time. Yes, yeast can convert carbs into simple sugars and into alcohol but not within the timeframe of making bread nor I would think in the medium of a dough rather than a wort as wouldn't be conducive for yeast to produce a lot of alcohol. Of course over time it'll produce alcohol as a by product e.g an over fermented dough or hooch in a starter but It wouldn't be as much as a beer - I would think!
So I would think the alcohol potential of a dough would fall far below a crafted beer.
P.s. I think the question has been answered. Seem to remember, think it was something Debra Wink mentioned, that LAB under certain conditions can produce acetic acid. Tom reminded me. So the acetic acid is not coming from converted alcohol. I was making some wine when the question occurred to me and I was thinking about acetic acid being converted from alcohol forgetting about the LAB.
My original point was that both brewers and sourdough bakers exert some control over the fermentation processes while acknowledging that beer requires more time than sourdough baking.
Then the discussion seemed to become a digression pitting sourdough against beer. Either or, but not both. I want a table with both beer and sourdough on it.
And an even fuller table and pantry with olive oil, various cheeses, hard apple cider, vinegar, pickles and relish, coffee, real vanilla, chocolate, kombucha, mushrooms, miso. buttermilk, and lots more. We wouldn't have any of these without microorganisms.
Some of these are spontaneously fermented and can hardly be improved upon. Other foods may benefit or perhaps different varieties can be obtained by selecting special strains of microbes or controlling the time allowed for or adjusting some of the conditions for fermentation.
And the time required for some is obviously longer than others. My understanding is that about 9-months are needed for fermentation and processing of harvested vanilla beans into the elixir many of us crave. And real vanilla contains more than 250 flavor and fragrance components most of which are missing from synthetic vanilla. And we all know that wines, and some beers, and cheese can be aged for varying lengths of time.
Aren't microorganisms wonderful and where would we be without them!
However, as Tom said, they have to have the sugar available to do so. My original thought was breadmaking doesn't produce enough alcohol to make a lot of alcohol and certainly not enough alcohol and time to make acetic acid. But then Tom reminded me that the bacteria which make lactic acid, under certain conditions, can produce acetic acid.