The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

How do the gas bubbles (alveoli) evolve in size?

DanAyo's picture
DanAyo

How do the gas bubbles (alveoli) evolve in size?

How do the alveoli evolve in size? Are large bubble born that way? Are large bubbles the result of smaller bubbles that coalesce? How come all small bubbles don't grow into larger ones?

The question was birthed as Doc.Dough observed in another Video TEST when he asked, "where do the big bubbles go"?  His question intrigued me.

I made an initial 30 second YouTube video so that we could observe the alveoli in a 180 gram 123 SD over a period of 12 hours. When viewing the video you can change the playback setting in YouTube to slow it down if you choose. I set mine at 25% in order to get a better visual.

Lets put our heads together and try to learn more about this elusive process. 

Here is the first test video. https://www.youtube.com/watch?v=3jwmYxYrM_0

Here is the second test video. https://www.youtube.com/watch?v=2PAm50fGBCI This test differentiates in the 123 SD mix. 10% whole spelt and 5% whole rye where added to the mix. There is also a good visual to indicate the areas of under and over-proofing. These videos provide a window, via time lapse video into the inner workings of a bread dough. I recommend pausing the video at various stages to study the clock in order to evaluate the time lapse to produce a given proof or bubble growth. The test starts at about 8PM and runs through ~8AM.

Time lapse video test 3 was fairly uneventful, IMO. I decided to try covering the top of the dough with water to see what would happen. See this video here. https://www.youtube.com/watch?v=ri0Cm8v_YFk

Test 4 was using a Ciabatta style dough. 85% hydration 12.3% white flour and 350 slap and folds. https://www.youtube.com/watch?v=xtucjcPaZNY

Please reply with observations, thoughts, and more questions. I would also like ideas for improvements for a possible next video dealing with this subject. I am mulling over the thought of videos that will display comparative testing. I hope to video 2 or more doughs rising at the same time in the same video. The thought of comparing various flours, or different hydrations, or maybe even various percentages of levain in multiple doughs at the same time is intriguing. I think the information will be beneficial to myself and others.

Danny

kendalm's picture
kendalm

just watched to multiple overproof vid - are you sure you're from Louisiana ? You sound like a new Yorker ! Ha ha, anyhow, all of your loaves looked real mature to me even the first, by loaf 3 or 4 boy I felt like i could smell the sourness by then !

heres an observation - btw I looove your lame ! We are talking about big bubbles and as you slash in every case we see rather large bubbles in the interior. FTR I am of the opinion that you will get bigger 'holes' should you see scattered small alveoli as in a mm in diameter. I like to think of this analogy - blow up a balloon with one breath. The balloon doubles in size (or thereabouts). Now keep inflating to say 6 inches. Observe the balloon and now add one more breath. It ain't much bigger.  that is to say that thr amount of energy needed to double the size of a small alveoli verses a much larger one is geometric function (if we care to math it out).  that's all within the scope of one single gas cavity and within the dough many compete for space amd if we assume good proofing such that they all exhibit the integrity needed to contain the expanding gases - then fewer small alveoili should lend better to more larger 'holes' since there is more real estate to grow. Case In point when i slash i am scanning for scattered small alveoli and real lively young looking dough. That's not to say that matrure dough can't produce fantastic bread. As mentioned before, ive made some incredible pizza with well overproofed dough it's just a different animal entirely. All in all - I love this video but I think you started on the overproofed zone and went well into the geriatric realm !  

DanAyo's picture
DanAyo

https://youtu.be/VdYLi1qeozI It shows that first run of the test. NOTE; the video linked is part of THIS POST. The first loave baked at 50 minute proof. Have you evaluated those? I ran two test. My goal was to go from grossly under proofed to grossly over-proofed. The second video definitely went over-proofed. I jumped for joy when I finally produced a pan cake. I think it took almost 6 hours proofing to get there.

Dan

Oh! The accent. I try to sound educated on the video, but I’m Cajun all the way...

gary.turner's picture
gary.turner

This answer is derived from Bread Science and from private correspondence with the author, Emily Buehler, PhD (chemistry).

First, the CO₂ produced by the yeast does not cause the alveoli. The physics are not there. The interior pressure (P) is related to the radius (r) by the equation: P = 2γ/r, where γ is the tension on the outside of the bubble.

As is seen, for a new bubble, radius = 0, the interior pressure must approach the infinite. Not happening. Instead, the CO₂ enters into solution in the dough. It out-gasses only into an existing alveolus. From where do these bubbles come? They are bubbles created in the mixing and kneading stages. The kneading has two primary purposes (gluten development/alignment aside); working air evenly into the dough and distributing yeast throughout the dough.

The initial size of the alveoli are primarily determined by how you work the dough. The punch down is aimed at making big bubbles into small bubbles. Expelling gas is not the goal. Your aggressiveness here will determine whether you end up with a sandwich bread or one that provides a place for the baker to nap. The final punch down and shaping is the most important time for this control.

The large bubbles can eat the smaller because the pressure differential between them may be enough to break the gluten or lipid membrane between them. As a note of interest, if the amount of solid fat is sufficient, it will replace the gluten for a stronger film.

gary

DanAyo's picture
DanAyo

Please elaborate - “First, the CO₂ produced by the yeast does not cause the alveoli. The physics are not there. The interior pressure (P) is related to the radius (r) by the equation: P = 2γ/r, where γ is the tension on the outside of the bubble. As is seen, for a new bubble, radius = 0, the interior pressure must approach the infinite. Not happening.”

I recently read that the alveoli are a result of air pockets that originate (from mixing, dry flour, folding, and other such manipulations) in the dough. Gasses fill these voids and because the gluten network contains that gas, the bubble (alveoli) expands. So the yeast gas don’t produce the cavity, it just expands it. Is this correct?

I’ve been thinking... If the above paragraph is true, might it be beneficial to machine mix a dough very wet (similar to Ciabatta) and then after incorporating many air pockets, slowly add the remaining flour. My hope is to highly aerate the dough with the mixer, then introducing the remaining water to achieve the desired hydration. The idea is based on the thought that Ciabatta almost always produces extremely open crumb. Is this a viable idea?

 

gary.turner's picture
gary.turner

Quote:
So the yeast gas don’t produce the cavity, it just expands it. Is this correct?
Yes. More next …

Quote:
If the above paragraph is true, might it be beneficial to machine mix a dough very wet (similar to Ciabatta) and then after incorporating many air pockets …

Is this a viable idea?

It is something I do for a different reason.  I use a liquid pre-ferment, either a poolish or 100% hydration sour-dough added to all the additional liquid.  Then mix at fairly high speed.  My intent is to jump-start yeast's hanky panky.  Fast oxygen-fed reproduction gets the yeast off to a robust start.  Brewers pitch their yeast and strongly rouse the wort.  The yeast feed and reproduce strongly until the oxygen is gone then switch to an anærobic mode, making alcohol and CO₂.

I'd think any decent method of mixing/kneading will work plenty of bubbles into the dough.  The loaf's volume will be about the same with either large or small alveoli.

Pay attention to your handling of the dough while kneading and punching down.  Avoid expelling the gas.  Let your hands set the size of the bubbles.

gary

DanAyo's picture
DanAyo

Gary, you wrote, "Pay attention to your handling of the dough while kneading and punching down.  Avoid expelling the gas.  Let your hands set the size of the bubbles."

gary.turner's picture
gary.turner

Is there a question there, Dan, or are you emphasizing what I said?  I do consider that an important issue of kneading and shaping.

g

DanAyo's picture
DanAyo

Sorry Gary, there was a complete responce but for some reason I didn’t get it posted.

Gary, you wrote, "Pay attention to your handling of the dough while kneading and punching down.  Avoid expelling the gas.  Let your hands set the size of the bubbles."

I’ve run quite a few video test recently, and I think I may have reason to rethink my procedured when it come to BF and proofing. I have had a difficult time accepting the advice of some very accomplished bakers when it comes to BF. Quite a few recommend 30-50% increase for complete BF. The recent Under/Over-proof test and also Leslies latest test tells me that I am proofing too long. After watching a number of these videos in slo-mo, I think I see a pattern. I plan to stop my BF at 30-50% and proof very modestly (if I don’t opt to retard). My doughs don’t bloom as much as Id’ like and the ears are most often absent. Hopefully with this young dough things will change. But only testing it out by baking will prove it out or not. I hope to get the extreme open crumb in the oven, not on the bench. But I always plan to be gentle when handling and shaping the dough. We’ll see.

Dan

kendalm's picture
kendalm

wow if it takes essentially infinity psi or any pressure unit for that matter to form a bubble from nothing then where would the gas go should there (in a hypothetical case) be no initial bubbles.? Would it just dissolve into the dough ?

makes me think about soda - actually yes this makes sense. It's a known fact that soda explodes when you shake it - reason is you are creating more bubbles mechanically which then act as nucleation points - a bit like snowflakes needing a dust particle.  whoa daddy !

 

 

DanAyo's picture
DanAyo

Here is the second test video. https://www.youtube.com/watch?v=2PAm50fGBCI 

This test differentiates in the 123 SD mix. 10% whole spelt and 5% whole rye where added to the mix. There is also a good visual to indicate the areas of under and over-proofing. These videos provide a window, via time lapse video into the inner workings of a bread dough. I recommend pausing the video at various stages to study the clock in order to evaluate the time lapse to produce a given proof or bubble growth. The test starts at about 8PM and runs through ~8AM.

Bigblue's picture
Bigblue

Love your vids. I watched this several times. Very helpful. Thanks. Keep them coming :)

WatertownNewbie's picture
WatertownNewbie

Wow, what a lot of time and effort devoted to helping all of us gain a better understanding of what is going on during proofing.  The two videos with the blue glove were tremendous, especially when played at 0.25 speed.  The experiments with the spaced bakes were great too.  One question I have for those bakes was whether you could tell from a taste test which loaves were which (i.e., did the flavor change as the proofing progressed further?).

Thanks again.

DanAyo's picture
DanAyo

WaterTown, I am a big fan of "sour" sourdough. For my taste, none of them hit the mark. These loaves were destined for the neighborhood. It's not to say, they didn't taste good for many people, just not my kind of bread.

The breads were baked for testing, with no thought for flavor.

Dan

HKbreadwinner's picture
HKbreadwinner

to tape how fermentation progresses, and to see the maximum point of over-proofing.  And it was absolutely fascinating to see how the aveoli evolve over time.  Subjective to what wants to achieve, but to me, the optimal point for big aveoli development was at about 6-6.5 hours (I think at about the 2:15PM mark).   After 7 hours the gas bubbles just start to consolidate and collapse.  The interesting observation though, and this is where it gets confusing, is that at the 6-6.5 hour mark, the dough already grew to 3 times!  That's obviously way beyond what anyone recommends.  So based on people's 20/30%-50% growth recommendation, that should yield insignificant bubbles judging from your video.  So the question still remains.  Where the heck are those big bubbles? From baking?  I mean, I see them at 6.5 hours in your video, but isn't that way overproofed at 3x growth?  Lastly, how does Trevor J. Wilson and the Tartine book instruct 20% growth and still achieve those wildly open crumbs?  The agony, lol.  I need to review Maurisio and Trevor's comments from a couple weeks ago on my chat regarding fermentation time.

Also, what temperature did you ferment these at?  My ambient temp is easily 80%, and at six hours my dough MIGHT double (more like 75% growth), but definitely not triple. 

Again, thanks for always exploring and feeding our curiosities!

DanAyo's picture
DanAyo

HK, I’ve done a number of these test videos, so I’m not sure which video you are referencing. But each video has a temperature/humidity meter in the shot. I think they ran @ 77F.

So @ 6-6.5 hr the dough appears strong, but carefully watch the video after that. Notice how the bubbles rise to the top and burst. I think the dough @ 6 hr is much weaker than it appears. Imagine what will happen to the bubbles, when to the heat of the oven causes the gas within to expand?

RE: BF proof. On this subject my thoughts are evolving. Prior to testing I found it difficult to accept the advice of guys like Trevor and Maurizio regarding 30-50% increase for the BF. I thought (like you wrote) that if I bulked longer the bubbles would grow larger and the resulting crumb would reflect that. I thought, all I had to do was be extremely careful when shaping. BUT, maybe I was looking at that wrong. I studied the videos considering the buubles. Yes, the bubbles are nice and large @ 3 times growth, but haven’t they become extremely weak and fragile? Is it possible the ability of the yeast to produce additional gas is in the process of becoming exhausted? Will these large beautiful (but weak) bubbles be strong and resilient enough to survive shaping? And what happens when these bubbles (if they survive the handling) hit the heat of the oven? Will they be able to expand and cause the loaf to bloom? (NOTE - notice in the video what happens to the bubbles after the extreme rise.) Then I thought, no wonder my scores don’t open hugely and produces erect ears. The dough is tired, weak, and out of gas.

At this point, it is only a concept. I haven’t proved this yet, but I plan to exercise extreme discipline and stop the BF much earlier than usual. Also, after the Under/Over-Proof testing, I think I am proofing too long. My next goal is to prepare a relatively “young” dough for the oven, with hopes of huge bloom and tall ears. I think the magic might occur in the oven when moist, super heats expands the gases, enlarges, the alveoli, and rips those ears wide open. Hey! A guy can dream :-)

Dan

littlelisa's picture
littlelisa

This is fascinating stuff, Dan. Thank you for taking the time to share this with us! 

I was intrigued to see the blue glove slightly inflate and deflate over the course of the proofing/overproofing process. For me this was visual evidence of the excess of gas being produced within the container. (Genius idea to use the glove like that, avoiding the pitfall of a tightly closed container, but still sealing in the gases and thus demonstrating how gas content increases in there. 

I was also intrigued at the point you note, at which most artisanal bakers stop the bulk ferment. Are you talking here about time or about size/feel of dough as indicator that it's time to stop? I would usually expect my dough to double (or perhaps even triple) during the BF stage, and I kind of stop it by feel - sometimes shorter than recipe sometimes longer, but basically when the size looks "right" to me in relation to the dough ball it was when unproofed. (I know! So unscientific!) I was just curious as the dough in the experiment didn't appear to have doubled at all. 

 

With regards the water - I suppose water is heavier than air/gas (which is why the float test would work to demonstrate fermentation), so as the dough ferments and produces gas, the water would gradually work its way through the permeable membranes or holes in the dough, and fall to the bottom, no?

And, as an aside, I found your earlier video (the staggered bakes demonstrating stages of overproof) also fascinating. Particularly fascinating to me was that your first loaf had a quality of texture to the dough (kind of widening or webbing areas at the surface) that I would normally take as indicators of overproof already. Yet it wasn't overproofed. Clearly some of my own "look and feel" parameters don't apply the same to SD. When you slashed your unbaked loaves, the appearance was like cutting through the skin of an overripe brie! This is an appearance I've never noticed in non-SD baking (normal lean artisanal loaf, made with commercial yeast), but obviously I have to change my visual calibrations in this brave new SD world :-)

Thanks again

Lisa

HKbreadwinner's picture
HKbreadwinner

Hi Lisa, when you double (or even triple) your bulk size, what hydration are you using for your dough?  Is the dough shapeable without severely deflating at 80 and above?

littlelisa's picture
littlelisa

Hi HKB, 
It occurs to me now that I'm talking about non-SD doughs, as I took such a long break from making bread with wild leaven. My non-SD doughs are shapeable after doubling or tripling, yes. Does the wild yeast type make a big difference to extensibility/slackness? I'm guessing yes...

 

Lisa

DanAyo's picture
DanAyo

Lisa, you wrote, For me this was visual evidence of the excess of gas being produced within the container.” That made me think the the gas was escaping the dough, which is a bad thing. But, maybe it is the gas expanding within the dough, and as the dough expands so does the glove. Similar to putting a ballon in the vessels wiith the rubber glove on top. Then somehow inflating the ballon. That would make the glove rise. Im not sure if gas was s escaping the dough or not, but it is an interesting question. Maybe someone else can help with this. I did notice that near the end of the video that the glove would begin to deflate. I can’t explain that either.

Concerning the BF, take a look AT THIS?

 

You mentioned the dough looking like “over ripe brie”. The dry skin was an error on my part.  The skins dried out because I proofed all 8 loaves on a covered couche, and I didn’t have a plastic bag large enough to encase them. Next time - a huge garbage bag :-)

Dan

 

littlelisa's picture
littlelisa

Hi Dan - regarding the gas being produced - yes, it would be produced inside the dough, causing the volume of the dough to expand. The dough increases in volume, pushing up and forcing the air above it upwards (displacement?), thus pushing the glove up. When the dough starts deflating, its reduced volume allows the air above to to shift downwards again, hence the glove wobbling back down. 

I never really get round to covering loaves in plastic as I'm usually proofing batard-type shapes on a big wooden board (note to self: get round to getting some long oval baskets). This was never an issue with my non-SD breads, but I'm noticing a definite "cheese-skin" effect from the longer rises SD likes. 

 

Lisa

littlelisa's picture
littlelisa

ok, for me this is the hardest hardest thing. I always feel like I'm in the dark at this point. 
Dan, you wrote:
"After watching a number of these videos in slo-mo, I think I see a pattern. I plan to stop my BF at 30-50% and proof very modestly (if I don’t opt to retard). My doughs don’t bloom as much as Id’ like and the ears are most often absent."
I used to think it was the windowpane test that indicated the point at which you stopped the BF. But I've had that belief blown away because now people seem to develop to windowpane at mixing stage. THen leave for a BF. And it's not doubling volume. What is the sign? A sort of airy lightness to the dough? that's all I look for... that in combination with time. But... so vague...

DanAyo's picture
DanAyo

Lisa, you wrote, "The dough increases in volume, pushing up and forcing the air above it upwards (displacement?), thus pushing the glove up. When the dough starts deflating, its reduced volume allows the air above to to shift downwards again, hence the glove wobbling back down."     This is what I don't get about the rising and lowering of the glove. The glove rises because the gas produced by fermentation increases and that causes the dough to rise pushing the glove up. But even though it is true that as the dough falls so does the glove, what happened to the gas that caused the dough to rise?

I am under the impression that the dough fell because the gluten got weak over time and allowed the gas to escape the dough. But what happened to the gas? Didn't it rise from the weakened dough and remain in the vessel? How was the pressure reduced, enabling the glove to fall?

Maybe this example can explain my thought. Lets say you have 2 balloons, and 1 is placed inside the other. So now the smaller balloon is inside the larger and both are moderately filled with air and sealed closed. Now the smaller balloon develops a tiny pin hole and begins to leak air until it starts to collapse. Even though the smaller balloon is deflating and decreasing is size, wouldn't the larger balloon maintain it's original size because the escaped gas from the smaller balloon is still trapped inside the larger one? 

I appreciate the help

Dan

gary.turner's picture
gary.turner

 You provide an interesting question. Have you considered the CO₂ may have re-entered solution in the dough. In that case, the total volume will closely approach the volume of the pre-rise dough.

g

littlelisa's picture
littlelisa

Dan, you wrote: "But even though it is true that as the dough falls so does the glove, what happened to the gas that caused the dough to rise?" I too am scratching my head! I am no physicist (I'd love for someone more confident in physics to be able to explain this to us).

Gary's suggestion that the CO2 may have partly dissolved makes some sense to me. 

But also: Is it possible that at the point that the gases are produced by the yeast, their temperature is fairly warm because of the heat released by the fermentation, and also being in close contact with the fermenting dough? As the dough falls and releases the gas, it diffuses into the air in the container and also decreases in temp... contracting. In fact all the air enclosed by the glove would surely undergo a gradual drop in temp as the fermentation activity drops. 


DanAyo's picture
DanAyo

Teresa Greenway claims that the CO2 is absorbed into the dough during cold retard. And that because of this the dough blooms greatly in the warm oven.

I don’t understand that one also. Would love to get an understanding of how CO2 acts within a dough. 

Dan

pipaid's picture
pipaid

The amount of gas that can be dissolved in water depends on temperature and the gas' pressure.  In general more gas can be dissolved at lower temperatures, and when the pressure drops and/or temperature increases, then the excess gas comes out of solution and forms bubbles.  Think about opening carbonated beverages: the sudden pressure drop creates a lot of bubbles, and there are more bubbles in warm beverages than in cold.  This is the reason for ice-filled champagne bowls.

This may or may not apply to dough: after all, a significant portion of the dough is water, but on the other hand, the bigger portion of the dough is not water.  If it does apply, then it could explain Teresa Greenway's claims: refrigerated dough could absorb more of the generated CO2 than at room temperature, so then there is more CO2 to come out when the dough is heated in the oven, potentially causing more oven spring.  I don't know how significant the difference might be.

Another possible implication is that dissolved gasses don't contribute to rising of the dough, so in the cold the yeast has to work harder, and eat and digest more for the same volume increase.