The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Starter Bubbles, Bottom to Top?

Mebake's picture

Starter Bubbles, Bottom to Top?

When i refresh My sourdough starter, i see bubbles through the glass container that start to appear at the base, and then appear higher as fermentation proceeds. Why aren't bubbles appearing throughout the starter altogether?

Some food for thought..

Edit: Does the same apply to a dough built from a starter?

Could TFL members explain why is that?


cranbo's picture

someone correct me if I'm wrong, but isn't the gas generated by yeast CO2, aka carbon dioxide?

Just like a soda pop, bubbles will rise, and the CO2 is bubbling out of the starter solution, escaping into the air out of the weak (early) structure of the dough.

Could also be that the bubbles form more easily at the bottom because they are supported by the dough, while the bubbles at the top are escaping more easily, and you don't see them at the top until a certain point, when the structure at the bottom of the dough starts to weaken.

Just a couple of W.A.Gs...

Mebake's picture

Thanks, cranbo, but a soda pop has carbonic acid which is saturated with c02 under pressure. You are right about the weight of the dough at the bottom. I'am thinking gravity is one reason for it..

Mini Oven's picture
Mini Oven

we'd be talking about evenly spread bubbles of different sizes.  (Spin to deflate!)

We also could be talking about air pressure?  Air pressure weighing down the air bubbles in the dough?  High altitude baking has a problem with the CO2 rising too fast, less air pressure.  

So it stands to reason that 5 meters under sea level, in an underwater kitchen,  the bread dough may need more leavening power.  Any body underwater?  Submarine maybe?  

Mini in a yellow submarine

davidg618's picture


Submarines are maintained at one atmosphere pressure, so bread dough behaves the same at sea level, and 20,000 leagues under the sea in a submarine.

Otherwise, there's a whole lot of physics and chemistry going on when carbon dioxide is disolved in an aqueous solution. Partial pressure of CO2 at the interface between the dough and the air or container material is probably he biggest contributer to initial bubbles forming on the bottom, and, shortly following, the top surface. If the partial pressure of CO2 is the culpret, dough should behave similarly in zero-G, i.e, bubbles would first appear at the surface of the dough mass.

Baking the dough in zero-G might be a bit more of a challenge. Perhaps an Astro-pan de mie would work?

David G

dmsnyder's picture

I can't buy the gravity/pressure theory. The dough at the bottom of the bowl is under more pressure (from the mass of dough above it) than the dough at the top. The CO2 bubbles at the bottom should be more compressed than those at the top.

My suspicion is that the differential in CO2 production is due to differences in oxygen, there being more O2 where the dough is more exposed to the air. I think what you are seeing is more CO2 being produced in the anaerobic conditions deep in the dough.

Another factor may be temperature differential. If the surface of the dough is cooler, fermentation is more active in the depths of the dough.


Mebake's picture

Thanks, David, It could be all of the above... Cranbo, Mini, DavidG, and David.