June 8, 2012 - 10:27am
Let's talk bread theory - overproofing
I'm trying to clarify my understanding of overproofing. Here's my definition: overproofing is when fermentation has strained gluten to its limit. In other words, when gas buildup has stretched gluten to its breaking point. Is this an accurate understanding? Are there are other adverse effects to the dough that I am not accounting for? According to this, 2 identical doughs, although one using high gluten flour and the other using AP, rising in identical environments will overproove at different times, due to the diference in their gluten contents?
Also, can overproofed dough just be given a new forming and new rise and achieve the originally intended quality? Has gluten been destroyed from the overproofing?
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Hello Breadhead,
A discussion of over-proofing could also take into account the dough being spent. In other words, there is no food for the yeast to feed on. In this case, re-shaping the dough, which you ask about, is a waste of time; as is the hope of adding some colouration to the dough by baking the final product for longer. Would you argue that this comes into "over-proofing"?
Best wishes
Andy
Andy,
Good point. If the sugars have all been consumed then the bread can longer rise, nor can you get caramelization on your crust. My gut tells my that that isn't what's immediatly meant by overproofing, but this is something to consider here as well. I wonder if there is a way to calculate the amount of sugars in the flour, and the rate at which the organisms consume them. Also, I hope the pun in my subject line wasn't too terrible.
BH
When I do to my dough what I call over-proofing, I have left it proof for so long that there is little or no potential for rise left in the dough. If I am lucky, it will bake in the shape it is now. If I am unlucky, it will collapse during baking because it was on the way to collapsing anyway. At best, without oven spring it is a slightly denser bread and a bit harder, too, if baked by the same method. I associate this with lack of remaining nutrients, and nothing I can do with shaping will cure that. Nor would more gluten have helped.
Aha! So this is like Andy is saying. I guess the consumption of the sugars is a real issue. Could you guestimate how long this happens in? How drastic are your overproofing times? Were they doughs at room temp or in the refridgerator?
My doughs are proofed at room temperature. In the worst case the bread had been proofing probably twice as long as it should have, in other words, about two to two-and-a-half hours. The dough had begun to slouch over the edges of the pan. I baked it immediately, starting with a cold oven and leaving off any lid. A lid wasn't possible anyway, with the dough hanging over the sides. The bread flattened down just a bit and was harder than normal, but was edible. A less severe time it had only been maybe a fifty percent too long and the dough was just starting to encroach on the edges of the pan. I put a lid on and baked as normal. A tiny bit of dough cooked out between the lid and the pan, making the bread look like a plastic molded item which has not been trimmed. Again it was a little hard, but not fallen. These experiences occurred this spring, and reminded me to pay better attention to the dough in warmer weather!
Do you think if you would have re-kneaded the dough at that point it would've re-risen as normal? Like hitting a reset button?
No, I think it would have not risen again. At least not the worst one. If it had any nutrient left, it would have had some oven spring. At that point, also, it would have begun digesting the gluten and making ketones. These don't smell edible.
It's possible that one could add flour and water, and restart the process. In effect, using the dough as a large preferment. But you'd have to make several more loaves than just the one you intended to make.
As a thought, I suppose you could add a tablespoon of sugar to the exhausted dough. I'm not sure what that would taste like.
Oven spring has little to do with residual nutrients in the dough. It is all about the expansion of the trapped CO2 and the resulting volume increase of the foam that is the bread.
If the dough leaks CO2 it is overproofed whether or not there is sugar remaining; if the yeast runs out of food the dough may be underproofed or overproofed.
The dough may leak gas for many reasons, including breakdown of the gluten due to acidity.
Emily Beuhler disagrees with you on oven spring. According to her, one factor is a final burst of fermentation as the dough heats up in the oven. There are also chemical reactions occuring. It is not purely a mechanical process of a biologically and chemically inert system.
I think, for the rest, it becomes obvious that both gluten and yeast nutrients play a part in when a dough collapses. Perhaps those of us who use strong flour probably tend to run out of nutrients before the gluten is ruined, while those who use weaker flour tend to blow out the gluten structure before the nutrients are used up.
Therefore the phenomenom that is called overproofing is a physical state of collapse of the foam which contains carbon dioxide, and not always the result of one particular mode of failure.
Seem reasonable?
I have heard the claim that there is a last gasp by the yeast between oven entry and yeast expiration, but when I run the numbers it doesn't work out.
If you have an analysis that says otherwise I would love to be wrong.
Hi Doc,
For arguements' sake, if your final proof holds the dough at 30*C, then it will take several minutes in the oven before all of the dough reaches 53*C and the yeasts are killed off. So there will be a last burst of yeast activity. Even though the yeast is nearing the end of its life, the temperatures close to our body temperature are those most favoured by yeast. If you are thinking there is no yeast activity at the point when the dough is set in the oven, then, I suggest that the dough is actually spent, and the bread produced will be rubbish. If this were the case, the yeasts would die because they had run out of food. That means no residual sugars in the dough, which, in turn means no dough structure, and, no caramelisation either. So, love away, you are wrong about this. A final burst of yeast activity does play significant role in oven spring.
Best wishes
Andy
That explains why the very over-proofed bread was pale as well as flattened and harder. No sugars left for carmelization. Thank you!
Yes the yeast is still alive when the bread goes into the oven. Yes there is still some sugar left in the dough. But the two much larger contributors to oven spring are the (already produced) trapped CO2 in the bubbles and the trapped CO2 that is dissolved in the dough. And if you retard the dough, a lot of the CO2 that is produced goes into solution and not immediately into volume expansion. When you put it in the oven with steam, the surface (within a few seconds) goes to the high 90's (°C) and the surface becomes pretty impermeable to diffusion of CO2. The second thing that happens is that the dissolved CO2 begins to come out of solution and (in low hydration doughs) form blisters or begin expanding the outer surface of the dough. As the temperature of the dough rises, the trapped CO2 expands according to PV=nRT. The strength of the dough will determine to some extent how much volume expansion occurs, but the reconfiguration of the dough to maximize the ratio of volume to surface area opens up the slash marks, makes a baguette round, and makes a boule become more spherical as it bakes.
The yeast which has over a couple of hours perhaps doubled the volume of the loaf, has the capacity to produce CO2 at perhaps 2x the average rate of gas production during the proofing phase. 100% volume growth in 120 minutes is slightly less than 1% per minute; 2x would be 2% per minute; the volume growth rate during oven spring is very high within the first 2 minutes; it can't be dominated by the yeast contribution since the only yeast that is affected by increased temperature is in the outer few % of the diameter. It is this fraction of the total dough that participates in the (hypothetical, back of the envelope, unverified, speculative, ...) 2% per minute maximum so if the participating fraction of the loaf is 5%, then volume expansion rate due to yeast is 0.1% per minute for at most 10 min. Someplace I have a spreadsheet with all of this in finer detail but you get the idea.
So I am not convinced. But I have ordered Emily Buehler's Bread Science anyway, just because it sounds like a terrific resource and a fun read.
Emily Buehler, "Bread Science", second printing 2009, pages 186 and 187. For obvious reasons I can't pass on the chart, but she has a plot of temperature at the crust and in the center, versus time. According to her, oven spring is mostly complete in the first 10 minutes.
She says at 60 degrees C yeast dies and starch gelation begins. For the crust this is in about 7 minutes. For the center this is in about 12 minutes. By the time the temperature reached 80 degrees C, the starch gel is sufficient to support the bread. The gluten denatures, all enzymes are deactivated, and carbon dioxide, water, and ethanol escapes. The crust reaches this temperature in about 9 minutes. The center reaches this temperature in about 15 minutes.
Hence one of the important factors behind the use of steam. It delays crust formation, and therefore helps to maximise oven spring
Andy
There may be also a small release of dissolved CO2. The solubility of CO2 decreases with increased temperature (try heating beer or soda water). Some CO2 generated during proofing will have been dissolved in the water and this will probably come out of solution as the temperature rises. But this could be a minor effect.
I take it to be that over-proofing for most people is indeed to do with the dough losing the ability to hold its structure.
As a dough rises its structure becomes more fragile. The localised strength in any given area decreases as the overall mass increases. A dough on the more extensible side will start to blow bubbles when over-proofing occurs. A dough on the stronger side will remain at its full capacity until it slumps.
For the most part an over-proofed dough could be punched down and re-shaped. Although considerations must be made.
As Andy pointed out a dough may be "spent" and not have enough available sugar for the yeast to raise the dough again. This is a likely outcome where too much yeast or leaven has been used. Providing the gluten is still in good shape this situation can be remedied by remixing the dough with some yeast-food, specifically a sugar that yeast can consume directly; maltose or glucose - these sugars can pass through the cell wall of the yeast and be converted to CO2 and alcohol straightaway.
In the case of sourdough enzymatic reactions occur more rapidly simply because there are more of them. The gluten structure will weaken much more quickly than with a yeasted dough. This needs to be considered also.
Hopefully this sheds some more light on the nature of over-proofing.
Michael
In other words, if it has been formulated to withstand an additional rise, both in gluten content and in nutrients versus yeast, you can punch it down and let it rise again, but if not, you can't. *chuckle*
Not really. Most doughs by default can withstand many rises, especially yeasted ones. No formulation required.
Aditionally yeast food availability isn't a set thing. Enzymes are at work converting starch into simple sugars.
I was basing my comment on your assertion that a dough should never run out of nutrients unless too much levian was used. I happen to think my dough performs very well for the conditions under which it is intended to perform. The fact that I can't cause it to double three or more times does not mean it is made incorrectly. It just means that it is formulated to rise twice and be baked, without spending more than half a day at the job.
Michael,
I had hoped someone would mention enzymes!
All good wishes
Andy
I aim to please :)