# Bread dough - CO2 cannot itself form bubbles, it must diffuse into existing bubbles? **URL:** \ **Category:** Factual Questions\ **Created:** [March 16, 2008, 2:28am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517 "2008-03-16T02:28:53Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 16, 2008, 2:28am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/1 "2008-03-16T02:28:53Z")
I was discussing bread making with someone on another forum - he’s a fairly experienced baker, by all accounts - he stated that carbon dioxide produced by yeast cannot, of itself, form bubbles in the dough - it can only diffuse into existing bubbles of ordinary air that have been incorporated during initial mixing. The assertion comes supported by citation of [this](http://books.google.co.uk/books?id=EKGUPlEwP5MC&pg=PA94&lpg=PA94&dq=%22the+origin+of+the+gas+cell+in+bread+dough%22+baker+mize&source=web&ots=7Uo4VQaGeL&sig=kayJVBSEpDiuI6LO1WoyeWWsKI8&hl=en#PPA94,M1) book - which looks like it’s pretty established science. So my question is: why is this the case? Why cannot CO[sub]2[/sub] excreted by yeast, in dough, produce its own bubbles? ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [March 16, 2008, 2:41am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/2 "2008-03-16T02:41:30Z")
Well CO2 forms plenty of bubbles when I open a can of soda, and I don’t think there’s any ordinary air there. It could contain some dissolved oxygen as well I guess. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 16, 2008, 2:43am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/3 "2008-03-16T02:43:59Z")
Sure, but that’s not yeast making the bubbles - it’s coming out of solution. ---
**Author:** ![sjc](https://avatars.discourse-cdn.com/v4/letter/s/e5b9ba/32.png) [@sjc](https://boards.straightdope.com/u/sjc)\ **Post date:** [March 16, 2008, 2:57am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/4 "2008-03-16T02:57:32Z")
My first thought is that it’s not so much that the CO2 _can’t_ form bubbles, more that it doesn’t do it very well on its own (at least for the purposes of making bread). As far as I know, however, CO2 may not be able to make the bubbles in bread on its own, but my intuition is that the situation is closer to the one I stated. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 16, 2008, 8:38am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/5 "2008-03-16T08:38:29Z")
This book goes into a little more detail: [Technology of Breadmaking](http://books.google.com/books?id=qJiSXi0vgXoC&pg=PA21&dq=%22Technology+of+Breadmaking%22+nitrogen&sig=h7JqVnfOdktxOKkmUegSPRszci4) > [@](#): > > Carbon dioxide gas has many special properties and at this point we are concerned with two: its high solubility and its relative inability to form gas bubbles. As the yeast produces carbon dioxide gas, the latter goes into solution in the aqueous phase within the dough. Eventually the solution becomes saturated and unable to hold any further carbon dioxide which may be produced. The rate at which saturation occurs depends on fermentation conditions, but is fairly fast in all breadmaking processes, as shown by the rapid expansion of the dough as the gas is retained within the developing or developed dough structure. > If the carbon dioxide does not form its own gas bubbles how then does the expansion of the dough through gas retention occur? Two other gases are available in significant quantities within the dough as a result of mixing… Carbon dioxide’s high solubility and relative inability to form gas bubbles are directly related to its propensity to form carbonic acid in water. (see [this post](http://boards.straightdope.com/sdmb/showthread.php?p=3275873&highlight=supersaturated#post3275873) in the thread " Pressing Scientific Issue: Do Pump-Caps Preserve Soda Fizz?, Part II") The slow CO[sub]2[/sub]/carbonic acid equilibrium essentially [buffers](http://en.wikipedia.org/wiki/Buffer_solution) the carbon dioxide concentration at saturation. Since bubbles form in _super_-saturated solutions, CO[sub]2[/sub] isn’t as quick to form them as most other gases. ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\ **Post date:** [March 16, 2008, 10:03am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/6 "2008-03-16T10:03:05Z")
The problem might be one of bubble _nucleation_, the formation of initial, very small bubbles. There is a substantial energy hurdle to get over for small bubbles to form. This is related to the phenomenon of _superheating_, where clean water heated in a smooth-sided vessel such as a test tube can be raised substantially above boiling point without forming steam. When a successful nucleation event finally occurs, a whole lot of water turns to steam at once, “bumping” the water. To prevent this from happening, “anti-bumping” stones can be added to provide bubble nucleation sites, so the water boils continuously rather than going through superheating and bumping cycles. Yeast forms CO2 slowly, and it will initially go into solution in water in the dough. When the water is saturated with CO2 it will “want” to come out and form bubbles. But if bubble nucleation is hard, it will require a degree of supersaturation before the bubbles can form. If the CO2 is diffusing into existing bubbles and making them grow, the supersaturation will never be achieved and so CO2 won’t form its own bubbles. I guess this is important because it’ll affect the texture of the bread. The more pre-existing bubbles there are to act as nuclei, the finer the bubble distribution will be, which is probably a matter of how much kneading was done. The tendency for dissolved CO2 to form carbonic acid is a complication, but I’d bet on bubble nucleation being the most important factor here. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [March 16, 2008, 5:46pm UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/7 "2008-03-16T17:46:52Z")
let’s try that again: [QUOTE=matt] The tendency for dissolved CO2 to form carbonic acid is a complication, but I’d bet on bubble nucleation being the most important factor here. [/QUOTE] I expect there’s more than one correct answer here. Bread dough is a complicated system, and it’s easy to find critical variables. Here’s a bit on [CO[sub]2[/sub] supersaturation:](http://www.atypon-link.com/ICE/doi/abs/10.1205/096030898531828?cookieSet=1&journalCode=fbio) > [@](#): > > Proving of bread dough was modelled using classical one-component diffusion theory, to describe the rate of growth of bubbles surrounded by liquid dough containing dissolved carbon dioxide. The resulting differential equation was integrated numerically to predict the effect of initial bubble size and system parameters (carbon dioxide concentration, surface tension at the bubble interface, temperature) on bubble growth. Two situations exist, potentially; the dough could be either supersaturated or subsaturated with carbon dioxide. When the dough is supersaturated, the model predicts a critical bubble size above which bubbles grow indefinitely, while below the critical bubble size bubbles reach a limiting size and stop growing. I’ve made bread of both hole types. The trick is in controlling it so you get the size distribution you want. Apparently, even [vacuum cycling](http://www.freepatentsonline.com/70160709.html) can be useful in making some types of bread doughs. It’s time to drag the vacuum pump out of the basement. 😉 ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 17, 2008, 10:35am UTC](https://boards.straightdope.com/t/bread-dough-co2-cannot-itself-form-bubbles-it-must-diffuse-into-existing-bubbles/441517/8 "2008-03-17T10:35:03Z")
So is this one of those ideal gas law/partial pressure things? - that the CO[sub]2[/sub] exists in solution at a concentration not sufficient to emerge as its own bubbles, but more than sufficient to compel it to mix with existing bubbles that contain a low concentration of the gas?