Flavour & Fire
The Sourdough Journal
Bulk Fermentation
This is where the waiting becomes the work.
After mixing and the first stages of dough development, there comes a point where doing less becomes part of the process. During bulk fermentation, the dough is given time to develop as a whole, while the microorganisms in the starter continue to ferment the available sugars, producing gas, acids and a growing complexity of flavour. The structure you began to develop through mixing and folding continues to change, gradually allowing the dough to become lighter, stronger and more capable of holding what fermentation creates.
It can be tempting to think of this as the quiet part of sourdough, because for much of it, you are simply leaving a bowl of dough on the counter. Yet beneath that still surface, the dough is changing constantly. Temperature, time, flour, starter activity and dough strength are all working together, which is why bulk fermentation is less about watching a clock and more about learning to recognise what the dough is telling you.
What Is Bulk Fermentation?
Bulk fermentation is the main fermentation period after the dough has been mixed and before it is divided and shaped. The dough remains together as one mass, giving fermentation time to develop while the structure continues to strengthen and organise.
During this stage, the microorganisms in the starter consume available sugars and produce carbon dioxide and organic acids as part of fermentation. Some of the carbon dioxide becomes trapped within the developing dough structure, creating the bubbles and aeration that will eventually contribute to the texture of the baked loaf. At the same time, fermentation produces compounds that gradually influence the flavour and aroma of the dough.
This is the stage where something you have mixed begins to become something you can shape.
What Happens During Bulk Fermentation?
Several processes are taking place at the same time, and they are closely connected. As fermentation produces carbon dioxide, the dough becomes increasingly aerated, while the developing gluten structure gives those gases somewhere to collect and remain. With time, the dough may become smoother, lighter and more elastic, and its volume will gradually increase as fermentation progresses.
But fermentation is not only about making the dough rise. The activity of the starter also changes the flavour and character of the dough, with organic acids and other fermentation products contributing to the distinctive qualities of sourdough. How noticeable these changes become depends on the conditions in which the dough is fermenting, which is why two loaves made from the same recipe can develop quite differently.
The recipe gives you the ingredients.
Fermentation gives them time to become something more.
Time and Temperature
Temperature is one of the strongest influences on the speed of fermentation. A warmer dough will generally ferment more quickly, while a cooler dough takes longer, meaning that the same recipe can behave very differently from one kitchen to another and even from one day to the next.
This is why a fixed instruction such as “bulk ferment for four hours” can only ever be a starting point. The temperature of the dough, the strength and activity of the starter, the amount of starter used and the flour itself all influence how quickly fermentation progresses. Even the temperature of the room can shift enough over the course of a day to change what those four hours actually mean.
The clock tells you how long the dough has been fermenting. The dough tells you what those hours have done.
How Do You Know When Bulk Fermentation Is Ready?
One of the most useful skills in sourdough is learning to recognise when the dough has moved far enough through fermentation to continue to the next stage. Rather than waiting for one precise visual signal, you are looking for several changes that begin to appear together.
As fermentation progresses, the dough will usually become lighter and more aerated, with bubbles developing within the dough and sometimes becoming visible along the sides or underneath. The surface may become gently rounded or slightly domed, and when you move the bowl, the dough can develop a soft, lively wobble rather than sitting heavily in place.
Exactly what you see will depend on the dough you are making. Hydration, flour type, temperature, starter activity and dough strength all influence its appearance and behaviour, so there is no single shape or percentage of rise that can define readiness for every sourdough.
You are learning to read a combination of signs.
Underproofed or Overproofed?
Bulk fermentation can stop too early, but it can also continue for too long, and both situations leave their own clues in the dough.
When fermentation has not progressed far enough, the dough may still feel dense and relatively tight, with less aeration and development than you would expect. It may not yet have the strength and elasticity needed to move comfortably into shaping, because the fermentation process has simply not had enough time to progress.
When fermentation goes too far, the balance can shift in the other direction. The dough may become increasingly slack and fragile, losing tension more easily and becoming difficult to handle without disturbing the structure and gas it has already developed.
Neither situation is simply a matter of the clock being right or wrong. Fermentation is a moving process, and recognising where your dough is within that process becomes much easier when you learn to combine time with what you can actually see and feel.
When Should You Stop Folding?
The folds from the previous stage are particularly useful during the earlier part of bulk fermentation, when the dough is still developing the structure it needs to support fermentation. As time passes, however, the dough becomes increasingly aerated and delicate, and the purpose of handling it gradually changes.
At some point, another fold is no longer helping the dough develop. It is simply disturbing what the dough has already built.
There is no universal number of folds that tells you exactly when this moment has arrived. A dough that still feels loose and spreads quickly may benefit from another gentle fold, while a dough that has developed tension, holds itself together and shows signs of fermentation may be better left undisturbed. As the bulk progresses, the emphasis slowly moves away from building more structure and towards protecting the structure and gas already present.
Sometimes the most useful thing you can do is nothing at all.
Bulk Fermentation Is Not Just About Volume
It is easy to reduce bulk fermentation to one question: How much has the dough risen? Volume is certainly useful, but it is only one part of the picture.
A dough can increase substantially in volume while still lacking the balance of structure and fermentation needed for shaping, just as another dough may show plenty of activity without appearing dramatically larger. The amount of rise you see is influenced by the dough itself, the flour, hydration, temperature and the strength of its structure, so treating one particular percentage as a universal rule can be misleading.
This is why bakers learn to read the dough rather than relying on a single measurement. Time and temperature give you context; volume, bubbles, texture, elasticity and movement provide the clues that help you understand what is actually happening.
The more often you make sourdough, the easier those clues become to recognise.
From Bulk Fermentation to Shaping
Eventually, the dough reaches a point where it has done enough. Fermentation has developed gas and flavour, the structure has matured, and the dough has enough strength to be handled without immediately losing everything it has built.
Now the purpose of the process changes.
Instead of allowing the dough to continue developing as one mass, you begin preparing it for its final form. The next stages — shaping, cold proofing and scoring — will ask you to handle that structure carefully, preserving as much of the fermentation you have spent hours creating as possible.
Bulk fermentation is the quiet middle of the sourdough process. You give the dough time, and in return, it gives you signs. The skill is learning to recognise when those signs are telling you to keep waiting — and when they are telling you it is time to move on.
This is where the waiting becomes the work.