Important note to keep in mind: Bulk fermentation is slow and the window of when it is complete is large. Err on the safe side if you are unsure. The point at which the dough is ready for shaping can be an hour and in a cooler kitchen, sometimes more.
Bulk fermentation is the stage after the dough has been mixed. It is called Bulk because in a bakery it is the stage before the dough is divided ready to shape and proof. It is when the dough is fermented in bulk. It is the stage when the gluten network is developed in home baking. Fully developed gluten is the cornerstone of every good loaf. It is perhaps the most important stage of bread baking.
Commercial bakers do most of the gluten development in a mixer. This enables them to do a brief bulk fermentation saving them time and money. The cost to them is poor bread flavour, as good flavour is brewed into the bread through longer fermentation times. Here I assume that a mixer, if used at all, is only used to bring the ingredients together and perhaps sixty seconds or so on slow speed to get the dough started.
What does Bulk Fermentation Do?
It is the stage where the gluten network is developed.
It is where most of the fermentation takes place creating the bread's flavour.
Gluten Network development – Breaking the Bonds
When first mixed the gluten proteins form weak bonds with each other. Kneading (which includes slap and fold, coil folding, lift and folds etc) breaks these bonds by mechanical action. This is like snapping a twig. Once those bonds are broken, they cannot reform. Instead, different bonds form where the sulphur atoms on the end of each gluten molecule binds the sulphur atoms on the gluten near to it. This is often referred to as the S-S bond in baking. These bonds are strong and they are the foundation of a strong CO2 trapping gluten network. For this reason, I favour either a brief 60 second machine knead (slowest speed) after the flour has hydrated at the beginning, or five or six minutes of slap and folding. Slap and folding is very effective for breaking the weak bonds. This is the preferred method used in France for this very reason. However, which ever method you choose will work. Throughout bulk fermentation more weak bonds are being formed and the stretch and folds continue to break them allowing the S-S bonds to replace them.
Gluten development and time
Gluten develops naturally over time. Machine kneading puts energy into the dough which increases the rate of gluten formation. We as home bakers want to ferment the dough for a longer period to allow the flavour to develop. The gluten network will form along the way.
Building sheets of gluten
When gluten first develops strong S-S bonds, the proteins are tightly coiled. Being coiled up they cannot trap CO2 to allow the dough to rise. We need to stretch these coils out into gas trapping sheets. We do this by repeated stretch and folds, laminating the dough, or coil folding. As the coils are stretched out the dough becomes more elastic because the coils are more fully extended. In the rest intervals the dough relaxes again as more coiled chains are formed and as the gluten sheets pull back like rubber no longer under tension. By repeatedly stretching the gluten network and folding it over itself we gradually form multi layered sheets of gluten with superior gas trapping ability.
Tearing the gluten
Despite the S-S bonds being strong they can be broken. Forcing the stretching will break the bonds. Once broken they cannot reform. If this happens the dough is better repurposed as flat breads, or if it is very bad, as a chapati, or roti which require very weak gluten.
It’s immediately apparent when the gluten is being torn as the surface of the dough takes on a shaggy appearance. These are the torn gluten edges. If these are seen, stop immediately and let the dough rest and relax. No further stretching is possible at that point.
The old ways of kneading
There are two very traditional ways of kneading. The oldest which has been used across the bread baking world from Persia to North Africa and East Russia to the Nordic countries, is to place the dough in a container such as a wide bowl or trough and then to repeatedly push clenched fists into it, first left then right then left again. Every now and then the baker will take one side of the dough and fold it across to the other side. It is a form of ‘stretch and folding’.
The fist push method gave way, in some traditions, to ‘heel of hand’ kneading. This is more violent and it can easily tear the gluten sheets with weaker doughs. Here the heel of the hand stretches the dough away from the baker before it is folded back onto itself, the dough is then turned through 90 degrees and the process repeated.
Both of these are a lot of work, but they develop the gluten quickly.
Now with higher hydration the gentler stretching and folding methods are often preferred.
How much gluten development can we expect to develop
Many of us look at the flour packet and the first thing we want to know is the amount of protein in the flour. What we cannot easily find out is how much of that protein is Glutenin (the precursor of gluten) and how much of it is Gliadin, another protein. Gluten gives the dough elasticity. That is the ability to snap back after being stretched, like a spring. Gliadin allows the dough to be extensible. That is, it lets us stretch the dough more without it springing back. In bread baking we need both. Good modern strong bread flour has about 2/3 glutenin and 1/3 gliadin. Heritage wheats are often nearer 50:50 gluten and gliadin. Additionally gluten is a family of proteins not a single particular one, some types are stronger than others. Some form stronger bonds than others. For this reason, millers do a number of tests to see how strong (elastic) that particular flour is. Gluten strength can vary depending on the ground in which it is grown along with the weather, particularly the amount of sunshine the plants receive.
When we have a poorer quality flour, we must stretch the gluten more gently and reduce the amount of stretching we do. Those gluten networks are more delicate. Heritage wheats, and ancient varieties such as Khorasan (Kamut in the U.S.), Emmer, Spelt and Einkorn, all have weak gluten and they need gentle handling.
Fermenting flavour – The building Blocks
Another aspect of bulk fermentation is flavour development. This mainly comes from three sources. The natural pigment carotene, which gives flour a slightly off white, or yellowish colour. Carotenoids are flavour molecules. Vigorous machine mixing destroys them through oxidisation which occurs in vigorous machine mixing. So too does bleaching the flour. Most of the flavour in wheat is in the bran and germ. Slow milling Watermills and Windmills rub the fatty germ into the endosperm (the white flour), for this reason it is not then removed by bolting. These flours will make better flavoured breads. Using a little whole grain flour, even at 10% of the total amount of flour used, will make a ‘white bread’ much more flavoursome and at a mere 10% it will still have a soft white bread mouthfeel. These are our building blocks for fermenting flavour.
Fermenting Flavour the chemistry
As our dough ferments organic acids are produced by the yeast and the Lactobacilli (LABS), if we are using a natural leaven. LABS produce more acids and so stronger flavours are developed, but yeast produces acids too. Another source of acids is the CO2 itself. As it reaches saturation levels some of it dissolves into the water in the dough. When it dissolves it forms carbonic acid.
These acids react with the alcohol, which is produced by the yeast and together they form flavour molecules. The reactions are much slower than the yeast can rise a bread and so using too much yeast to get a faster fermentation works counter to flavour development. For this reason, when using instant yeast in bread I use the lower figure of the manufacturer’s scale of 1% - 0.66%, or more easily 3.15g / 1 level teaspoon to 500g of flour. Cold bulk fermentation and cold proofing are all about flavour development too. The flavour reactions are slowed, but they continue in the fridge. Whereas the yeast fermentation is pretty much halted at 10C–12C, 50F-54F.
These weak organic acids also react with the flavonoids in the bran and germ to produce flavour as well. The processes are so complex and interlinked biochemists have not yet been able to map them all.
The magic of degassing the dough
As we do our kneading (lift and folds, slap and folds, lamination, or coil folds), we degas the dough a little. That is, we expel CO2 from the dough. With less CO2 the dough is no longer saturated with it. When this happens a considerable amount of Carbonic acid comes out of solution in the water and the acidity of the dough falls. With lower acidity the yeast becomes more active. Some authors say folding air into the dough allows the yeast to be more active. This is not the case. It is the degassing and lower carbonic acid levels.
Later on, when shaping the dough, degassing will have a marked effect on the crumb. Heavy degassing will give a closer crumb whereas minimal degassing will give a crumb with larger alveoli (holes) with more larger holes. But once again it lowers the carbonic acid levels allowing the bread to proof more rapidly because of the lowered acidity. Degassing also redistributes CO2 in the alveoli, giving a more even crumb.
Of friends and foes in the dough
Flavour development can look after itself. The more time we give it the more flavour we will get.
These friends and foes are both the enzymes in the flour. Whole grain flours are higher in the enzymes found in the wheat germ. White flour too has some enzymes.
There are two key enzymes in flour which matter most to us. Both are crucial for making good bread and both can wreck a loaf if it is fermented for too long, or their levels are too high.
They are Amylase and Protease.
Amylase – These break down starch into maltose which is the sugar that yeast metabolises best. Sucrose is not easily metabolised by yeast. If you want to boost your bread add a little liquid malt to it and not sugar. An excess of time for amylase to act, or too much amylase, will break down too much starch. When we bake a loaf, it is the gluten structure which gives it structure when it goes into the oven. As it bakes it is the starch structure which takes over this role. If the starch is too degraded by the amylase the bread will collapse into a gummy mess in the oven. Freshly milled flours are high in enzymes and so they’re less tolerant of prolonged fermentation and cold fermentation in the fridge.
Some millers add amylase to their doughs. If you have such a flour, then long bulk fermentation is not advisable.
Protease – These sound like the very devil. They chemically cut up the gluten structure. This makes the bread more digestible, but again too much fermentation will cause too much gluten network damage resulting in a heavier bread. Again, this is evident in over-extended cold bulk fermentation and too long spent cold proofing in the fridge. That is why most bakers recommend 12-16 hours in the fridge only.
The gluten disruptors
A number of things are added to dough which disrupt the formation of the gluten network. These sometimes merely get in the way of the gluten molecules. Examples of these would be seeds, fruit and kibbled grains. It is best to add these later on in the bulk fermentation by using lamination. This is a process whereby the dough is stretched out into a sheet, sprinkled with the ingredient being added and then folding the dough up on itself with them inside.
Fats are another gluten network inhibitor. Fats coat particles and in this way they make it more difficult for bonds to form. For this reason the quantity used must be controlled. They also coat the starch packets making it more difficult for the amylase to break them down into sugars for the yeast. When working with weak glutens it is sometimes better to laminate fats into the dough after the first set of stretch and folds. The same goes for many other things we add to doughs from time to time.
If using lamination I do so in place of the second set of stretch and folds. Later on the gluten network can be too strong to allow for as much stretching.
Finally we have the issue of bran. Bran acts like small sharp knives which physically cut up the gluten network as we do our stretch and folds. When wholemeal, or whole grain flours are used it is important to handle the dough gently and if possible to reduce the number of stretch and folds to a minimum.
The phenomenon of accelerating dough rises.
After the dough is first mixed nothing much seems to happen. This is because yeast has a lag time. After yeast is introduced to a new environment, your dough, it can take up to about an hour before it starts fermenting. It is a yeast adjustment period. For this reason, I add my natural leaven at the beginning when I give my newly mixed dough a 30-minute to 45-minute rest to allow the flour to hydrate. Instant yeast is best added then too.
As the bulk fermentation continues so too does yeast multiplication. The yeast population will double about every two hours for a natural leaven and it doubles about every hour and a half for commercial yeast. At first nothing seems to be happening. The yeast is in its lag phase, but the gluten is still forming. After the first couple of hours of bulk fermentation there is twice as much yeast present and some dough rising is seen. After four hours there is four times as much yeast and the dough rises more rapidly. In the last hour of bulk fermentation, the dough rises in a satisfying brisk manner.
As we have seen bulk fermentation has to be slow and long to develop flavour, but not too long or the enzymes will do too much damage and that timing will vary depending on our flour. Especially if rye flour is used. It is very high in amylase. Broadly speaking the timing here is not critical. If the baker is sensible and follows the basic guidelines with cold fermentation and does not attempt excessively long worktop dough fermentation in a warm kitchen, the enzymes will not be a problem. They are something to be aware of with flours which have had amylase added, when using diastatic malt (very high in amylase), rye flour, or freshly milled flour. Typically, bulk fermentation takes around four to six hours in a warm place. That is 24C – 28C 75F – 82F
What intervals are best for coil folding
I have seen all sorts of recommendations and once drew up a chart listing many so that I could try to understand them. After trying out many I came to see that the timing is not that critical. What is important is how many.
We have seen that coil folding, or whatever method is being used, is used to stretch out the gluten sheets and fold them over to build a gluten structure. It also stops too much carbonic acid build up which allows our fermentation progresses a little faster. There is a baker’s rule. ‘Dough should never be left for more than two hours without something being done to it’. (J.Hamelman). I like to do some kneading immediately after the flour has hydrated. I will do my first folds at either thirty minutes or an hour later. Mostly I do them at one-hour intervals all the way through. If I am rushing the dough, I will do the first three folds at thirty-minute intervals, but that is for high-speed baking.
What matters more is how many sets of folds. With high hydration doughs I will do four sets. That is because languid coil folding is less effective than say slap and folds. With weak doughs I might only do two sets. There isn’t so much gluten to develop in them and it tears easily. Typically, I will do three sets.
Having said that, if the gluten structure isn’t developing very well, I will add another set in by shortening the intervals, not extending bulk fermentation time.
Double or Bust
The old adage of, ‘let the dough double in size’ is not a bad one, but it is only a rough guide.
Some competent home bakers swear by a 20% increase in dough volume for some loaves. I have let mine triple once or twice when using the baking technique called ‘Falling asleep’. They have all produced a good loaf. We can relax a little on this.
What we are trying to achieve is peak gluten development. As the dough ferments and as we do intermittent folds, the gluten structure gradually becomes stronger. However there comes a point of peak gluten development. This is when the gluten structure has developed to its maximum. After this point is reached its strength will diminish due to enzymatic action. It is this same enzymatic action that causes a preferment, or natural leaven to become more liquid as it ages.
The key measure is whether the dough is losing its elasticity during bulk fermentation. This is where folding at intervals comes in handy. After each set of folds, we should see an increase in the dough’s elasticity. If at any point the dough's elasticity, after folding, is much the same as at the previous set of folds, we have reached peak gluten development. Worse, if the dough has less elasticity after folding than previously, we have passed peak development and the dough should go straight on to shaping and proofing. In this deteriorating dough elasticity scenario, shorten the proofing time if you can. The enzymes have the dough on a downward slope and the sooner the dough goes into the oven the better.
The ideal is to move on to shaping and proofing just before peak gluten development is reached. Shaping is the equivalent to an extra set of folds and proofing is additional fermentation time.
Doughs with different flours will all have different peak gluten strengths. Some will reach that point a little sooner than others. Doughs with very strong gluten are more tolerant. The higher level of gluten means more can be lost during fermentation and the gluten structure will still be good.
If all else fails:
Bulk fermentation is complete when little extra strength is gained when doing coil folds or similar.
If you are unsure roughly go for the dough doubling, but a little less will be fine. Eventually experience kicks in and the baker just knows they’ve got the best gluten development they are going to get.
Tip: If the gluten is a long way past its peak, consider making flat breads. A flat bread will be light even with weaker gluten as it does not have to support the greater vertical weight of a loaf.
Preserving your hard won gluten network
I’ll cover this in more detail in another article. However, when moving on to shaping take great care not to fold unfermented flour into your dough. This will give you unfermented gluten which will weaken the structure you have built up. If the dough is too liquid for a free-form loaf, then bake it in a tin or pan, or switch to baking English Muffins in rings. Did I mention flat breads?
Use as little flour as you can when shaping and keep it underneath and the outside. Some baker folk use a thin smear of oil on their worktops.
With practice all but the wettest doughs need no flour on the worktop at all.
If during bulk fermentation something comes up and you won’t be able to keep to your schedule. There are two choices. If it is simply that you need to go out for an hour, then leave it to ferment. You can fit your interval folding into what time is left.
If the dough is going to be left for more than two hours then simply cover the dough to stop it drying out and pop it into the fridge, until such time as you can continue. That might be overnight in which case switch to cold bulk ferment methods the next day.
Bulk fermentation is part science and part craft. The length of time that should be allowed for it is not strict and the baker has quite a bit of leeway.
As stated at the beginning: Bulk fermentation is slow and the window of when it is complete is large. Err on the safe side if you are unsure. The point at which the dough is ready for shaping can be an hour and in a cooler kitchen, sometimes more.
Proofing, on the other hand, is time critical and sometimes even fifteen minutes can make the difference between a good loaf and a poor one.