Aerobic and anaerobic fermentation and how does it work?
Hello and greetings to the forum, which i have been reading for quite some time. Lots of infos and great people here, so first of all thank you for your whealthy knowledge.
I have been baking bread for some time now, not very successful for a long time (i really wanted to find out for myself without any books, and the internet wasn`t even around these days).I really started to get into it about a year ago with the discovery of Jim Lahey`s "no knead bread" again.
Some things in baking i could never wrap my head around but now i think i am beginning to understand how it all fits together. I hope you can help me solving these questions (and please excuse the lenghty explanation)...
I will start with the things i can't understand:
Slow fermentation:
Slow fermentation will give better bread than fast fermentation. When you aim for a longer proofing time you use less yeast or a lower temperature. But in reducing the amount of yeast or lowering the temperature you actually only reduce the rate of metabolism of the yeast. But for flavour and volume of the dough that is actually what you want to get: A lot of metabolism equals a lot of volume (CO2) and a lot of flavour (products of fermentation). By reducing the yeast you just slow down fermentation, changing the quantity without changing the quality of the fermentation, why should this give you a superior quality? (Just think about the absolute metabolism that takes place).
Depletion of sugar or substrate when the dough is overprooved:
Everybody is talking of depletion of sugars when the dough is at the end of proofing. There is a lot of substrate (starch) in a batch of flour. Yeast (as i understand it) can convert starch to sugar. So how can there possibly a deficit of it when it is sitting right in the middle of a whole lump of it? What is really depleted when your dough is overprooved?
Proofing and "2nd rise"
I understand the concept of proofing a dough, but why do you have to proof a dough a second time after shaping. Or, why do you have to shape the dough after the first rise at all and not bake it right away? Is it really only a matter of giving structure to the dough?
This is how i think it all makes sense again:
Yeast is a double action organism: If there is enough oxygen, it will do aerobic fermentation, which uses the oxygen for metabolism and mainly produces CO2, so leavening the dough. If oxygen is depleted, it will swich to anaerobic fermentation which mainly produces alcohol and flavorful compounds, but a lot less CO2.
In a long fermentation, yeast becomes starved of oxygen, because of depletion of it and of an atmosphere filled up with CO2. So it switches to anaerobic fermentation (ethanol fermentation) which produces all the flavourful substances.
In shaping the dough after proofing, you actually switch the yeast to aerobic fermentation again by introducing oxygen to the dough by handling it. The so-called "depletion of sugar" after proofing is really a depletion of oxygen which is reintoduced by shaping and will therefore be the start of a "second rise".
So the only reason for preferments like poolish, biga or old dough is to introduce anaerobic fermentation to your dough, so you just have to care about leavening with aerobic fermentation while baking?
Does that make sense at all? I would be glad to hear your opinions about these ideas.
Greetings from Berlin, Germany!
Nils
PS: As i am not an english native, excuse my mistakes or laborious wording...
I can drive a car but don't know all the workings of the engine. For an answer to all your questions you're going to need someone with far more in depth knowledge and the science behind bread.
However I can chime in with two points:
1. There is a difference between fermenting and proofing. Proofing is the result of fermenting. Something that is over fermented will always be over proofed. But something that is over proofed doesn't necessarily mean it's over fermented. Proofing is more about allowing the dough to rise to a certain amount that is best for baking allowing good oven spring. It can over proof but you can knock the dough back and proof again as long as it hasn't over fermented. But many use either term to mean the same thing. I just thought I'd comment on this but doesn't really answer your question.
2. Kind of ties in to my previous point. Shaping and final proofing is to create a loaf with a taut skin and allowing it to rise to a certain amount will give you a good loaf of bread. If it rises above the correct amount before baking it will collapse on itself. Think of it like a balloon being over stretched and popping. But in the bulk stage you aren't concerned about that just yet. You're doing the bulk ferment for flavour, good texture and you'll use this time to work on the gluten formation. So you bulk ferment till ready and depending on the dough/recipe etc it may rise more than the final proofing or not so. Then you shape it to strengthen the dough further and creating a loaf ready for final proofing.
P.s. your English is perfect!
Wow! That's a whole lot of questions and I hope other posters can fill in the blanks for you too.
Slow fermentation will give better bread than fast fermentation. "Better" is in the eye of the beholder. An open crumb and dark, chewy crust is very distasteful to a lot of people. Fast fermentation (or no fermentation) is generally targeted at production bakeries because they can churn out a lot of so-called "bread" and meet a production schedule. Slow fermentation is about developing flavors and textures, and isn't specific to yeast alone. Straight bread (yeast only) can be some of the most bland-tasting stuff out there. With that said, one way to develop flavors in straight bread is by using a fermentation process called a poolish.
Changing time, temperature and ingredients plays with the chemical composition of the ferment, and not just the pace of cell division. Bacteria and yeast try to adapt to these changes by changing the chemical environment in which the prosper and reproduce. Some conditions will favor bacterial growth and other conditions will favor yeast. These changes alter the development of certain sugars, and bacteria and yeast do not consume the same sugars. The byproducts of bacteria and yeast can result in better flavor or more oven spring (gas) depending on how you manage the environment of the ferment. There is much at play here and there is a wealth of information on this subject.
Depletion of sugar or substrate when the dough is overprooved: There will a point in time when the expansion of the bacterial and yeast colonies will exceed the available supply of starches and sugars. Anyone who has waited too long to proof and bake their bread will usually find that the dough turns to soup and not into a brick. When push comes to shove the living colonies go after the gluten and that is the end-stage in the life cycle of a loaf of bread.
During the fermentation process we bakers usually employ the stretch and fold method which serves two purposes. By gently working the dough we strengthen the gluten structure. We also redistribute the bacteria and yeast into new feeding grounds, which keeps them healthy and happy. Yes, there can be a lot of starch in the final mix... or maybe not. Some of my formulas use both a levain and a poolish, which are essentially depleted of starches when they are introduced to the final mix. If 40 percent of my final mix is already depleted, and the introduction of the levain and poolish include some very healthy, hungry and agressive bacteria and yeast, there really isn't as much available nutrition as you may think.
"(W)hy do you have to shape the dough after the first rise at all and not bake it right away" There are a couple of things at play here. Timing is a huge factor. Having the gluten development reach its peak at the same time as the maximum gas development, in concert with the maximum flavor development, requires a certain mastery to which we all aspire. Even the best of us are constantly humbled by the intricacies of bringing all these factors into play at the same time. Quite accurately you can bake a loaf of bread at anytime throughout this process but you may not end up with what you were expecting. Choose another time and you will end up with a different product. Most of us are striving to recreate something we like and we adhere to specific protocols in an effort to reach that end. IF you sell bread your customer is expecting the exact same loaf of bread today as they bought last time. As the saying goes, "Making bread is easy. Making good bread is hard, and making good bread consistently is nearly impossible."
Most of us here do not recognize the "first rise" theory, but instead work the dough over a series of hours. Slow fermentation means slow gas development so there really isn't a "punch down" moment in the process. Instead we ferment, divide, shape, proof, then bake over a multi-hour or even multi-day time period.
Whenever you handle the dough the gluten strands tighten. Think of it as a muscle that has cramped-up after a massage, that really still needs a lot of work. It is probably easier to wait for the muscle to relax before trying to work it again and that is why we wait between handling exercised. With that in mind we wait for the gluten to relax before trying to work the dough again. Moving too fast will tear the gluten strands that we worked so hard to build.
I hope this provides you with some answers to your questions. The subjects are very broad and I am simply skimming the surface on most of this stuff.
PS: Your English is 100% better than my German (nil)
Jim
Because yeast fermentation is not the only thing happening in the dough that produce flavor/aroma, and by slowing down fermentation you give them a chance to proceed.
No, starch is converted to fermentable sugars by ferments native to flour, natural or added. That's why yeast is eventually able to outcompete them.
Sometimes you don't. There are breads that are baked directly after the shaping, and there are breads that are shaped directly after mixing. But generally it is best to split it into rise and proof. Think about it this way - you want to give your bread a certain amount of fermentation time which results in certain gas production. That gas production could be too large for the bread to hold its shape, so you separate that excess into a separate preliminary step.
Forget respiration. There's never enough oxygen in the dough for that. For all practical purposes it's always fermentation.