Acetic Acid / Vinegar in Dough
I often explore different aspects of bread baking.
Recently I was looking at using Acetic Acid / Vinegar in direct baking doughs.
There is very little published (that I could find) in this subject. So I thought I would share what I have found.
Generally vinegar is used as a dough conditioner at about 1.5% of the weight of the flour. Vinegar is about 4% - 4.5% Acetic acid.
I wondered whether adding it would enable more flavour producing reactions with the alcohol produced by the yeast.
My intent was to make a simple bread add the acetic acid, ferment at 24C / 75F for a slow fermentation giving time for the flavour chemistry to work and then cold proof the dough for the same reason.
The bread was 80% moderate strength bread flour13% protein, 20% freshly milled whole rye flour, 0.0063% instant yeast and 60% hydration. Usually I would make this loaf with a natural leaven and so I have a good idea of the loaf volume, crumb and flavour.
The method used was
30 min flour hydration
A very brief machine knead, 30 seconds with a beater on the slowest setting.
3 episodes of stretch and fold over four hours
Stretch and fold shaping with moderate de-gassing, 14 hours in the fridge at 4C / 39F
Baked in cast iron cloche (challenger pan) at 230C / 446F.
Results:
The crumb was lighter and was nicely soft with that French Bread rubbery bite.
The crust was thin and crispy and had a good flavour and aroma.
There were no vinegary notes to the bread.
The fermentation was faster
The dough was more elastic, stronger gluten
Some of the colour was ‘bleached’ out of the dough. Oxidised carotenoids. Carotenoids are flavour molecules.
The flavour was diminished. Much poorer than this bread would ordinarily have with the whole rye flour.
Anyone reading this list should recognise precisely the same effects as those of adding Vit C / Ascorbic acid to the dough.
This bread had 20% whole rye in it. The crumb is usually a markedly denser than this with that amount of rye flour.
As a flavour enhancer it was a total fail.
I see King Arthur sell a dough conditioner which is acetic acid and Vital gluten.
I can only guess at what has happened. With naturally leavened breads the acetic acid is produced slowly and I suspect that allows more flavour reactions with the alcohol produced slowly by the yeast. Here I effectively dowsed the dough with ascetic acid and it has oxidised the gluten making it more elastic and it oxidised the carotenoids which give colour and flavour to the bread. This is precisely what vitamin C does to a dough.
Vinegar makes a superb dough conditioner if you don't mind the flavour loss.
Anyone got any more insights on this?
I used 2% Live Apple Cider Vinegar 4.5% Acetic acid
Sea salt at 1.8%
The effect of the vinegar are precisely what I would expect had I used VitC / Ascorbic acid, but it was easier to use than trying to weigh Ascorbic acid at 0.02g - 0.04g / kg of flour.
Apologies for the huge photo - I don't seem to be able to edit the post to place a smaller one.
Acetic acid and ascorbic acid are both organic acids, but they are very different in their properties.
Acetic acid should have no direct ability to oxidize the carotenoids in the flour. While it can be reduced to acetaldehyde or ethanol, it usually requires relatively strong reducing agents to accomplish. It may be possible that there are enzymes present in the flour that can catalyze this reaction.
There are enzymes in flour that allow ascorbic acid (normally an antioxidant) to oxidize bread dough. The ascorbic acid is oxidized by enzymes to dehydroascorbic acid, and that is what oxidizes the dough. When I returned to baking bread after many years, I was initially puzzled by the use of ascorbic acid as an oxidant. It wasn't till I read that an enzyme was involved that it made sense.
Another possibility could be that the acetic acid has disrupted the polyene (double bond) chain of the carotenoids, although I would think it would require a much stronger acid to cause this to happen.
I don't have a good chemical explanation for your empirical results. Maybe some other TFL members have some insight on this.
(Note: to reduce image size, you should be able to select the image after inserting and drag the frame to a smaller size.)
Thanks for coming back with those points.
Yes, agreeing about Ascorbic acid chemistry and that would suggest a different chemistry with ascorbic acid. In fact it may well have been your discussion here some years back which put me wise to that.
There was a very marked loss of colour and flavour to the dough. So much flavour and colour was lost I could have passed this off as a white bread, but for some bran flecks.
So, I think I can say 'something was done to the carcinoids, probably', nothing more. I take on board what you say.
There was a marked increase of the gluten elasticity as well. This I have assumed must have been. 'Oxidation', but again I don't have the chemistry on this to assert anything.
Your chemistry is already beyond mine on this.
Thanks for coming back. As a simple baker I know what the effect is now, but not the why. It would be great to know.
Thanks for the tip on picture resizing. I will remember for the future, that door seems to be closed now.
Thanks for sharing your bake Kevin however 99% of what you wrote needs addressing for its inaccuracies and faulty reasoning.
Industrially, vinegar is added to bread dough as a mould inhibitor and is not typically used as a dough conditioner as you stated.
Carotenoid pigments are not flavour compounds they are pigments. Colour can inform our preconception of how something will taste, however. Retention of these natural pigments can act a signifier of well-made artisanal bread.
Vitamin C.
Vitamin C or ascorbic acid can be added to bread dough to facilitate an enzymatic oxidation reaction which affects the thiol groups of proteins, by oxidising naturally occurring glutathione, this then mediates disulphide bonding (strengthening) of gluten proteins. This oxidation reaction does not cause oxidation of carotenoid pigments.
Vitamin C is not a bleaching agent - Not all oxidising agents are bleaching agents.
Utilising Vitamin C for gluten strengthening requires oxygen since itself is oxidised in the process. Oxyegn must therefore be actively incorporated through mixing to make it work effectively.
Ascorbic acid can be use as reducing agent by adjusting the dose and eliminating oxygen. Plant bakeries may make use of vacuum dough mixers to achieve this.
Ascorbic acid (lower dose) + molecular oxygen = Oxidiser
Ascorbic acid (higher dose) + vacuum = Reducing agent
Methodology
From what you write it suggests that you are comparing the qualities of this bake using yeast and vinegar to the same formula made with sourdough. If that is the case, then all your observations hold no weight because there is no equal basis on which to compare them.
In designing an experiment changing one thing at a time is a necessity to eliminate influence from other factors which may interfere with the results. Most people accept that sourdough bread taste better than yeast leavened bread. Comparing flavour between the two and attributing the difference to the effect of acetic acid is without foundation.
On the note of eliminating influence from other factors it would not be my choice to use live vinegar but distilled instead. Fresh milled flour could also be inconsistent.
Notes
Whole, freshly milled flour will be rich in enzymes including oxidising enzymes such as polyphenol oxidase and lipoxygenase enzymes from the bran and germ. Lipoxygenase enzymes oxidise lipids (fats) coming mostly from the germ and in doing so the reaction releases hydrogen peroxide H2O2 which invokes further oxidising reactions, including bleaching of the dough.
Adding acids may increase the redox potential, which therefore promotes the propensity for oxidation primarily with molecular oxygen present in the atmosphere.
I learnt today that Vinegar may contain ascorbic acid.
Further reading:
Organic acids in bread-making affecting gluten structure and digestibility
Insight into durum wheat Lpx-B1: a small gene family coding for the lipoxygenase responsible for carotenoid bleaching in mature grains
Michael
Yes, I am fully aware of the chemistry of vitamin C - I recognised that in a reply above. It is not so material to this experiment. The term bleaching was descriptive rather than chemical, it was in single inverted commas.
No, Vinegar is not solely added to commercial breads as an antifungal. Though that is an FDA approved use. It can also be added to dough as a conditioner as well. "Breads baked from wheat flours (protein contents 14.1–16.5% at 14.0% mb) that were pretreated with 2–3 mL of gaseous acetic acid per kg of wheat flour, showed maximum bread height and specific volume (cm3/g). Flour-water suspension and the crumb pH values were gradually decreased with increased amounts of acetic acid. Gas generation and dough expansion tests with bread dough showed that the addition of the same amount of acetic acid, which achieved maximum specific volume, also showed the highest rate of gas generation and dough expansion.
"Effect of Gaseous Acetic Acid on Dough Rheological and Breadmaking Properties"
From this and other scientific articles I have since read I am coming to the position that vinegar increases the extensibility of dough. Indeed I see that Bakerpedia make reference to this.
Excepting that I have baked with 20% Rye flour regularly over many years and using many different approaches. I think you are being a little pedantic in applying strict science methodology to this necessarily simple and subjective trial.
My sourdough bake of this bread develops good flavour and this comparative test is valid on those grounds. The question in my trial is on subjective differences regarding rheology and flavour differences.
Carotenoids are also a source of flavour molecules. "If the dough is overmixed, too much oxygen is incorporated and the carotenoid pigments (natural that are responsible for the creamy coproduction) will be negatively affect these pigments and automatically lead crumb color and a blander flavor." M Suas, (along with many others). And, that was a very notable outcome of this trial.
It is also noteworthy that K.A. use acetic acid in their dough conditioner.
After 20 years of home milling and using my current Landrace from the same harvest for some two years I think that, though you are technically correct the flour is fairly constant within my kitchen. Perhaps more consistency than if I had used a commercial flour with varied sourced wheats and which will has gone through quality control correction.
As for one variable at a time, you are correct, excepting that this is a real life experiment based on subjective assessment of dough behaviour and final taste, comparing two different baking methods.
Yes, you are again technically correct about using distilled vinegar and looking at your comment about Vit. C in vinegar, one might imagine apple cider vinegar might well have a raised Vit. C content.
Again, I am sure that you are technically correct. However should this simpleton response be acceptable: I have baked predominantly with whole grain flours for forty years and have never seen any notable evidence of this. So to that degree your observation is not useful in the real world.
I would add to this that if you are taking the metabolic pathway of "polyphenol oxidase and lipoxygenase enzymes" from your Durum semolina link below: I wonder if the production process was taken as a constant and I can well imagine that one issue might well be the inclusion of air (oxygen) during the intensive processing. My own home made durum pasta retains its colour.
All in all I have had to read a few science papers in order to make this reply. It appears that acetic acid:
Increases extensibility
Reduces the bread flavour
Is an anti microbial
Increases bread keeping qualities.
It's not so very useful to quality home bread baking in my book.
You appeared to be shoehorning scientific articles in rather than having a decent grasp of what might be happening here.
This is a sad day for me - You have always been a poster whom I have respected.
Please, in the future could we (all of us) not write things like this? They weaken the post and don't add to the helpfulness level that so many posts on this site offer.
I'd rather concentrate on the very interesting and important topic central your post - to what extent academic or theoretical information plays out in practical bread-making.
With respect,
TomP
Well Tom, out of respect for what you say I have edited that out.
You might have done better to have messaged me. I am reasonable and would have 'corrected' my post.
But, please, do not ignore the attitude of the post to which I replied.
Attitude? The hubris of absolute certainty, a lack of questioning and an attacking stance, rather than presenting evidence and enquiring.
The poster was out of order and evidentially wrong footed.
I don't feel comfortable posting here any more.
I hope that after some time goes by that you will feel more positive about posting again. I have gotten a lot out of reading your posts, and I'm sure that many others have too.
TomP