Thought I would share some general info on yeast fermentation and over proofing. My hope is that it may help someone by better understanding what is happening. This is based on my best current knowledge. It is written towards sourdoughs, but is equally valid for yeasted breads.
There are multiple things that occur during different stages of fermentation for sourdough breads. The actual fermentation process (yeast based) is exactly the same as with a regular yeasted bread. Each starter will vary – as will the specific yeast strains in the starter. They are commonly not as robust as commercial yeast. In any yeasted bread, there are two primary influences of how fast or slow fermentation occurs – the temperature and the amount of yeast added. For a regular yeasted bread – you might vary the amount of yeast from 0.2% to 2.5%. With all else equal, at room temp, this would cause a variation in fermentation time from ~12 hours to ~1 hour. The same is true for a starter. You can vary the amount of starter you add from 5% to 40%. There are other potential issues with a starter as you approach or go over 40%. (The starter is in the middle of it’s own fermentation process). At room temperature, this may cause a variation in fermentation time from ~12 hours to ~2 hours. This is more variable as each starter is different including how it is maintained and when it is used relative to it’s last feeding. Yeasts consume sugars and produce carbon dioxide and ethanol. This is the actual fermentation process. There are few natural sugars in flour and for sourdoughs, sugars are not frequently added to the dough.
The second process is the combining of proteins to form gluten. The dough can be mixed to “force” the proteins to combine or be allowed to develop gluten naturally (the proteins will combine naturally over time). Autolyse, no-knead, stretch and fold, etc. are examples of more natural gluten development. Different flours have varying amounts of gluten resulting in anything from weak to very strong gluten structures in the dough.
The third process occurring is activity from the enzymes naturally found in the flour. They are doing a couple significant things. They are busy converting starches (what flour mostly is) into sugars. This process begins when water is added to the flour(s) and continues throughout the fermentation process. It is also occurring during an autolyse. Different flours have different levels of enzyme activity. Enzyme activity can be increased by sprouting and drying the grain before milling. Commonly, the mill adjusts this by adding malted barley flour (sprouted and dried barley) as needed. The baker can also add diastic malted barley (typically <1%) or use sprouted flours to increase enzyme activity. The second thing happening is the enzymes are changing the gluten structure making the dough less elastic (returning to its original shape) and more extensible (able to be stretched).
The combination of these three processes is common for yeasted breads and sourdoughs. The visible rising of the bread is the result of the carbon dioxide produced by the yeast being trapped by the gluten structure. The bread dough inflates. The dough is also continuing to produce sugars, ethanol and the gluten is changing.
The level of enzyme activity, the strength of the gluten, the amount of yeast/starter added and the temperature all influence this process. A low gluten dough may not have the strength to double in volume. A very high gluten dough may triple. Overly enzymatic dough may overly damage the gluten resulting in a gummy bread. It is totally a balancing act.
The stronger the gluten structure, the longer the “window” is before the dough over proofs.
The poke test is a measure of the gluten state. Gluten has two main properties – elasticity and extensibility. As the dough ferments it fills with gas and stretches the gluten. If the dough is more elastic, when you poke it, it will resist and return to it’s shape (fill back in quickly). As the dough becomes more extensible – it will stretch and the indentation will tend to remain. You are looking for the point where the dough is more extensible but still has some elasticity. If the indent simply remains, you have lost elasticity. Time to move forward in the process. As hydration increases, this test becomes more difficult to use.
The general guidance of doubling is exactly that – general guidance. Some doughs may increase by only 75% while others by 200%.
My opinion is that it is better to err towards the under proofed side vs. over proofed.
If left untouched, the gluten structure will eventually fail and the dough will collapse. This in my view is a non recoverable error – it is simply better to start over. Anyone who keeps a lower hydration starter will observe this very thing. It will overproof, collapse and when stirred the gluten has no structure and the starter has changed consistency.
Degassing dough allows some (or all) of the trapped gases to escape. This allows the gluten to relax and by reshaping you restrengthen the gluten. It will begin to fill with gas again. However, the gluten has already become less elastic and more extensible. The dough will stretch more easily and the dough will “double” much more quickly. This is why a final proof is so much shorter than the bulk ferment.
For those who stretch and fold over a 2-3 hour period, each one partially degasses the dough and strengthens the gluten. You should not expect the dough to increase to the same extent during the bulk ferment as you have successively degassed the dough.
All of this is exactly the same for traditional yeasted doughs and sourdoughs. You have only changed the strain of yeasts doing the fermentation.
The bacteria (LAB) side of the starter also consumes sugars (different than the yeasts) and produces lactic and/or acetic acids. While the yeasts produce some acids, the LAB are much more efficient at it. The primary effect on the fermentation process is that as the dough acidifies, the yeast and LAB activity will slow. They also alter the gluten such that it is easier to digest – but do not seem to significantly impact its ability to retain trapped gas.
Over proofing is mostly an effect of the gluten strength – but also increases the ethanol content which impacts both yeast activity and gluten. It is not that the yeast have run out of food. When you degas and reshape – the enzymes continue to convert starches to sugars, the yeast consume them and produce CO2 and the dough rises again. The enzymes will eventually run out of starches to convert and fermentation will cease. The more yeast, the faster this will occur.
You are trying to find a balance of flavor (long fermentation), gluten extensibility (full lofty loaf) and color (enough sugars left for the crust to caramelize). For sourdoughs, you are also looking to manage how much acid is produced by the LAB – how sour, health benefits of easier digestibility and lower glycemic index and longer shelf life.
This question is one of the most challenging for the baker. When the same recipe is repetitively made using the same flours, the results will become predictable for the baker. Temperature becomes the biggest variable. When trying a new recipe or first learning, it is simply difficult. At some point – you come to understand how the flour will perform, how the hydration will influence things (higher hydrations weaken the gluten) and what to expect based on temperature. When learning – lean towards under proofing slightly. It will have a small impact on flavor and volume – but will produce a much better loaf than one from over proofed dough.
Watch the results from baking. If the dough rises substantially during the bake and tears open, it is likely under proofed somewhat. If you want the dramatic oven spring – under proof. Best wishes.