Questions For Discussion - I: Stirring Starters
I want to pose a number of questions that I hope will stir up some discussion. I have ideas about some of them but no real facts. Here's the first.
I have measured the volume of a starter as it rose after feeding. I've done this several times with various starters and a poolish. The general pattern was the same. The starter would, after a delay, start rising and build up to a roughly constant rate, then start to taper off.
If at this time I stirred the starter, it would naturally deflate and then start rising faster than before with little or no delay. I've even stirred it up again and again it would start to rise even faster. I also did this with a piece of dough, which I had to knead instead of stir, and got a similar pattern.
My overall question is: What is going on here? It comes with sub-questions:
1a. After the initial mixing of the starter, there is the usual delay before rising starts. But after stirring there isn't much if any delay. Why the difference?
1b. Wouldn't the handling during shaping act like kneading or stirring, and is this the reason proofing usually goes faster than bulk fermentation?
1c. Is there a way we can put this behavior to use?
Before any stirring, the samples I've measured increase in volume at a more-or-less constant rate. If there were a lot of multiplication of the yeast, the rate should increase since more yeast cells would be available to emit gas. I think this confirms what we're all taught, that the conditions during bulk fermentation are mainly anaerobic and the yeast cannot multiply. But why would there be faster growth right away - without that initial lag -after stirring?
TomP
Comments
Hi Tom, the overarching answer to a lot of this is CO2 saturation. You don't have it after initial mixing of the starter or dough, and so you'll see a delay in rise until the dough's water or starter reach CO2 saturation. Stirring may release gas that has expanded into the bubbles, but the dough or starter's water is still saturated at that point (and you have more cells producing it) so little to no delay. This interplays with the rheological state and limits of extensibility at a certain point.
Hi, Debra, very interesting. I've known about CO2 saturation, and that more gas can be dissolved at lower temperatures, But I have never been sure how much of a factor it is in practice.
How does this factor into the increased rate of volume increase after stirring the starter? Stirring increases the elasticity which, I would have thought, would not lead to an increased rate of the the expansion.
I've known about CO2 saturation, and that more gas can be dissolved at lower temperatures, But I have never been sure how much of a factor it is in practice.
I think it's important, but maybe the missing piece here is that microbes don't produce CO2 in the gas form. They produce and excrete it in the dissolved form, CO2 aqueous. It doesn't expand into gas (in the seed bubbles created in mixing) until saturation is reached, hence the initial delay in rise after addition of fresh flour and (unsaturated) water. And yes, the amount of dissolved CO2 that a starter or dough can hold is very much related to temperature.
How does this factor into the increased rate of volume increase after stirring the starter?
Stirring or kneading the starter releases (excess) gas from the bubbles. But the dough's water is still saturated. So any new CO2 produced at that point will be visible as rise. And you likely have more cells producing CO2 in full swing by then.
the conditions during bulk fermentation are mainly anaerobic and the yeast cannot multiply.
Yeast don't need oxygen to multiply in starter and dough.
This experiment by colinm ties in nicely with this topic, and you two even participated in that discussion ;-)
Oven Spring, Bulk Fermentation, and an Experiment | The Fresh Loaf
I do remember that thread and I don't seem to have taken anything very specific from it except for a general reassurance that one can shape or bake much earlier in the developmental cycle than is usually written about. These two conversations together are starting to gel things in my mind.
Following.