How much to bulk ferment sourdough?
Hello. This has confused me quite a bit from when i started making sourdough. I am used to having two rises, doubling in size, that you punch down with yeasted breads. But with sourdough its different. With my sourdough recipe, i usually let it rise 25-50% during bulk fermentation, and then retard in the fridge overnight (I am guessing it rises another like 40% in the fridge). I have had great results with this, but when the Youtuber, Foodgeek made a video about whether bulk fermentation affects open crumb, i was suprised. His results showed that the less you bulk ferment, the more open crumb and the more oven spring you get, and the more you bulk ferment, the more even crumb you get. (Video link: https://www.youtube.com/watch?v=eroSKcWzb4E) Can someone explain this? My guess is that if you shape early, with little bulk fermentation, the bubbles after the shaping gets to increase in size undisturbed. Whereas if you shape late into the bulk fermentation, all the bubbles that are in the dough gets kinda pushed down and spread more evenly into the crumb.
This just makes me think: 'Why are we even bulk fermenting then, if open crumb is what so many people want?' Would i be able to completely omit bulk fermentation for open crumb and great oven spring? And also, last but not least, Why are we not applying the same technique to yeasted breads? (Letting it rise less for more open crumb and better oven spring) Answers would be very appreciated :)
I don't think you can generalize like that as it depends on the fours, the makeup of dough, etc. as a dough needs to ripe to a certain point whether you call it bulk ferment or whatever. Some doughs will need a shorter fermentation while others require longer. With that said though, I think many people have a tendency to over ferment a dough thinking it would need more time.
Bulk fermentation builds flavors, so if you skip that step, you will either have a very bland bread or will need a very high percentage of pre-fermented flour to give you flavor.
https://www.thefreshloaf.com/node/70086/causes-oven-spring
All of the next statement is just my speculation after reading the thread linked above. I might be way off. :-)
According to the information in this thread, the two largest causes of oven spring are carbon dioxide gas getting forced out of the dough water and the dough water evaporating, especially into carbon dioxide gas bubbles (formed through fermentation). With no bulk fermentation, there's very little carbon dioxide gas to form bubbles and all the water evaporates into the weakest part of the dough (path of least resistance). That's why you see the large cavernous holes in an under fermented dough. So, for the FoodGeek findings, if you're somewhat under fermented, there's a little less carbon dioxide gas in the dough hydration and there's less existing carbon dioxide bubbles already formed. The water has fewer places to evaporate into (as compared to a fully fermented dough) and you get larger holes. Take a look at this bread I made yesterday. Decent hole size and distribution, but if you look at the dough between the large holes, you'll see it's pretty dense. Not a lot of tiny bubbles or airiness. This dough was very slow during bulk and just didn't rise as well as I wanted during final proof. Less CO2 bubbles formed and the water evaporated into the larger holes. Again, this is all my speculation at this point...
As Ming mentioned though, there's a lot more that goes into it than just fermentation. The bread above had 20% non gluten flours, which limits the amount and size of gas bubbles that can form. So that plays into the crumb structure too.
But what if you made up for the little to no bulk fermentation with a longer proof in the fridge?
I am currently trying it out. I made a dough, 63% hydration and 20% inoculation. I autolysed the flour while i was waiting for the starter, then mixed it and kneaded it for a total of like 7 minutes (until it passes windowpane). I preshaped and final shaped, and it is now in the fridge. I will be baking it tomorrow in about 24 hours. I am gonna send some pictures of it tomorrow.
I agree that the CO2 is going to be a function of time after mixing - the bugs don’t know that they are bulk fermenting or proofing, after all!
but I think there is something to shaping and getting skin tension, and taking out big air pockets from kneading/ folding in that shaping phase . TBH I’m sceptical that big holes are a function of fermentation at an under proofed stage (how is more fermentation going to remove those big holes, and fermentation is occurring right through the dough). So I think prolonging the physical things - stretch and fold and shaping gelos with evening out big holes and skin tension. But I like a longish proof. If all at room temp, my bulk is typically 3 hrs, and my proof about 4-5 hrs, pending temps etc. if I use the fudge overnight I will retard ~8 hrs if working from home, or ~20 hrs if not. Then I might bake anywhere from straight out of the fridge up to 2-3 hours warming up - it depends on what stage the dough is at!
I have wondered why this is, but then I have noticed that really underfermented dough does indeed form those long, large holes. I have a kind of mental model of why this is which is based on the behaviour of balloons, plus the observation that the rise in a loaf during baking is from CO2 leaving solution and from water evaporating into the bubbles. No doubt in an under-proofed loaf a larger amount of the rise is from water, not CO2.
Initially after mixing, we observe a few bubbles in the dough which slowly expand. I think they are mainly trapped air, but perhaps they are bubbles formed around places where there is a higher concentration of yeast cells. It takes time for small bubbles to appear in the dough in between those larger holes because bubbles behave a bit like balloons - the pressure needed to start a hole going and expand one when it is really small is much higher than that needed to expand one once it is larger.
The larger bubbles may not be so big during fermentation, but if the dough is baked before enough smaller bubbles form, the big bubbles will get bigger and bigger as their internal surfaces are the only places where water and CO2 can evaporate into the vapour phase. And like balloons (in the initial phases of inflation anyhow), the larger they get the less pressure it takes to inflate them even more.
But if baking is delayed and the dough is allowed to ferment further, the increasing rate of gas production will start to make bubbles in the dough in between the initial large bubbles. This can be observed through the side of a transparent mixing bowl, initially the space between the observable bubbles is smooth, then later on smaller pinhead-sized bubbles can be seen in it. This is actually not a bad test for when dough is getting ready (you will need your reading glasses though). Now if the dough is baked, the smaller bubbles collectively compete with the larger ones as places for water and CO2 to evaporate into, so the larger ones do not become monsters. Stretching, shaping and so on helps even bubble size out so the "larger bubbles grow quicker" effect is reduced.
I've seen this video. As a result, I now bulk ferment to 25%, (I use 30% inoculation/70% hydration) and have had great, reliable results.
I believe (and this is just my opinion) the reason why the shorter bulk fermentation time works so well is because the natural yeast still has a lot of "life" to give the bread during the final, (cold ferment) rise and initial bake. Initially, I was allowing my dough to rise so as to double in size, this almost always resulted in over proved dough and a flatter final loaf with a very closed crumb structure. Using 25% rise results in a very good ear, beautiful oven spring and a nice open crumb structure.
Just my experience, for what it is worth.