April 30, 2009 - 11:19am
Why should a levain be used at the peak of ripeness?
There has been some discussion lately about how to tell when a levain is ripe, but why is it important that a levain be used when it if ripe? Why not use it when it is half-way ripe or 3/4rds ripe?
--Pamela
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I see it as analogous to an athlete wanting to be at peak performance level for an event: you have the energy to perform at your highest level.
That includes man, yeast, and since the Kentucky Derby is this weekend - equines.
But doesn't the peak of ripeness mean that the levain is just about out of food/fuel?
--Pamela
Presuming you've built your levain from your culture in anticipation of using it in a final dough, the mixing of the levain with the rest of the ingredients will give it lots more muchies and keep it at peak peformance so it can do its job - which is to raise and flavor the bread.
At least, that's my humble theory.
Firstly I'm a relative newbie, I do however have experience with propagating and growing yeast in brewing.
Yeast and bacteria multiply in favourable conditions, producing their by-products as they do so, giving us what we want from them, namely, CO2 and acid ( in sourdough)
As their food supply dwindles they begin dying off in their own by-products and become less viable.
As new food is introduced into their environment, and a portion of their old "toxic" environment is removed, they resume multiplying. This cell growth continues untill something of a plateau is reached whereby the greatest number of viable cells for the available food is attained, just before they start dying off again. In this state, thay are considered most viable, and it is this peak condition that we want for our levain, so that there are the greatest number of viable cells to do the job of fermenting our dough, for the least amount of "spent" food.
Just my observations only, others more experienced will correct me where I'm inaccurate.
Paul
I don't doubt your humble theory, Lindy, but do wonder if there are other reasons involved since the levain is mixed with other ingredients before going through bulk fermentation.
I mean, on the one hand, we use a levain to prepare a piece of leavening (starter) for a batch of dough. If we just threw the starter in with the rest of the ingredients, then, I suppose, we wouldn't exactly-approximately know how long the dough might take for bulk fermentation. So we mix up a levain and run it almost out of fuel and throw it in with everything else and etc., and we know approximately how long things are going to take.
But, on the other hand, what would happen if we used a levain that was at half ripeness? Would the final dough's bulk fermentation proceed at a slower pace? Would the final loaf have less flavor and or less volume? I'm just wondering what the effect(s) would be.
--Pamela
Make some small loaves and use different timed starters in each one. If your starter takes 6 hours to get ripe. Try making a dough ball each with a 2 hour old, 4 hour old, 6 hour old and 8 hour old starters. If you want to time the experiment to watch them race together. Then prepare the 8 hour starter first, two hours later the 6 hr and so on when the last starter is 2 hours old. Mix up your 4 little dough balls and watch them grow. Even better, stuff them into 4 like glasses and mark them at hour intervals. Time them and see where the truth lies. This is only a suggestion but it might answer your questions.
Mini
I did think of running an experiment, but ugh! I'm just hoping someone knows why the levain should be at the peak of ripeness.
--Pamela
The couple of times I used my culture when it was a bit past its prime (by that I mean it had already peaked), either to make a levain or in place of the preferment, I noticed less rise and a less open crumb when compared to the same bread with a culture/levain at prime. I don't recall that flavor was impacted.
I had remarked on my thought that the strength of the levain had such effects in another thread (not sure which one), because I can't figure out any other cause.
To counter this, I now refresh my cultures just before I leave for work the day I plan to build a levain, so they'll be pretty much at prime when I get home. That restricts most baking for weekends, unfortunately.
The dough temperature has more of an effect on the length of the bulk fermentation than the strenth of the preferment. This is pointed out by Hamelman and our friend Dan DiMuzio, whose book just arrived here today (looks like a great read, Dan!).
If anyone is doing this experiment I would like to know the results.
But I'm not really sure how to rephrase it. However, if I ask about the goal of retarding, then I can answer by saying, e.g., that it delays the time it take for the dough to achieve maximum extensibility (gluten development) thereby maximizing CO2 development. At least that is what I think Suas is saying.
I'm trying to find a similar way of stating why we use a levain at the peak of ripeness.
--Pamela
If we let the levain go to ripeness then we have the maximum fermentation time which should equate with better tasting Bread. Also, I believe adding the Final Dough at that time also serves the purpose of refeeding the levain. So we get maximim advantage of the levain without over extending it so it will continue on strong.
I believe that others have expressed the same sentiments, but I'll dare to be redundant.
Why use a levain at its peak? Well, my first question would be: Why use any pre-ferment at its peak? My answer (since I seem to have degenerated into talking to myself) would be that the purpose of a pre ferment is to completely ferment the flour involved to gain additional flavor in the final loaf. So by cutting the pre fermentation process short, flavor would be compromised. Also, the acidity that comes from the pre ferment (which strengthens the gluten structure and results in improved keeping quality for the bread) would be less if the pre ferment was not mature.
Another consideration with a levain would be to have the yeast community at its most well fed and vibrant since you will not be adding additional yeast. By allowing the levain to fully ripen, you have gotten the maximum amount of yeast to develop in the amount of flour provided. I suppose that by using the pre ferment at a less mature stage, you would need a longer rise time for the dough - since you are starting with a smaller yeast community. In some cases this might be fine, but negates some of the benefits of a mature pre ferment if you were concerned with the timing your bakes or (as in the case of a professional bakery) leveraging time when you weren't paying staff. One of the advantages of the pre ferment is that it is mixed and then allowed to develop overnight - when in a small bakery no one is at work or is being paid.
Dough temperature is always important to rise time, but I would consider that when you are not dealing with commercial yeast, levain health is also a significant factor.
As for exhausting the available food, you are, of course giving the yeast a lot more food when you mix the dough, which leads me down another path. I just received the formula for Solveig Tofte's baguettes (which is not mine to share, so please, don't ask.) What was interesting (besides the relatively low hydration - something I've gone on and on about elsewhere) was the very high percentage of pre fermented flour. Because of this Ms Tofte adds malt so that the yeast does have additional food for the rest of the fermentations. Now, Ms Tofte is no slouch in the bagutte department - having done very well at the last Coupe du Monde, so I've been thinking about this a lot as of late in terms of how much flour I should be pre fermenting.
I have baked with an immature levain and I was most unhappy with the results. The bread didn't rise well and just wasn't - you know - "right." So I find it simple enough to give my pre ferment the time it needs.
Hope this helps.
When you use a levain at its peak then perhaps you are using it at the point when some kind of balance between maximum homo and hetero bacteria and a desirable yeast concentration has been reached so as to achieve a double goal with respect to flavor and proper extensibility of the final dough.
I'm trying to get beyond practical considerations such as timing, etc., and really figure out the role-goal of a pre-ferment/levain.
--Pamela
Of course, a pre ferment is something that has practical considerations - it is a compromise method that allows some of the flour to get a very long fermentation (and the benefits that come with it) - rather than retarding a whole batch of dough.
Mr Hamelman has a nice discussion of this on page 18 of his book, but being the kind of person I am, I have thought deeply about some of his formulas. He very rarely (if ever) recommends retarded fermentation for a bread made with a pre-ferment made with commercial yeast. Why? Because I speculate - in his mind - he has already brought the benefits of a long fermentation to the dough with the pre ferment and he needs to get about the business of getting the bread baked.
For naturally leavened breads, he will recommend retarding more often, to give the finished product a more acetic quality.
So, a pre ferment has goals similar to long slow fermentation if you are using commercial yeast.
With wild yeasts, I believe there is a secondary goal of getting enough yeast growth before any additional retarding so that the dough does not have to ferment so long that it develops more acid than it can really handle. While some acidification helps the gluten structure, too much can really cause problems and the gluten structure will be harmed.
Certainly with rye breads the acidifying of the dough is the primary reason for the pre ferment.
I let the levain ripen fully because I got bad results when I didn't. I actually got enough acid damage in my doughs to turn them to "glop" (a technical term) with an underdeveloped (or over developed) levain. They would start out like normal doughs (I baked with commercial yeast for a long time before I started the wild yeast baking in earnest, so I knew what bread dough should feel like) and then degrade into the aforementioned glop. Very unpleasant. My "sourdough" baking went from night to day when I took that one little step - so cold, hard experience stays my hand when I look at an unripe levain and think "Should I bake with this?"
Hope this helps.
I've taken another look at what Hamelman says on pg. 18: Benefits of Pre-Ferments. Thanks Lindy for bringing this page to my attention again. I've read it before but perhaps not with the same mind-set as today.
What Hamelman is saying now makes a lot of sense. We use a preferment/levain in order to accomplish extensibility, which occurs as a result of the acidity of the preferment. Other factors include flavor developement, keeping quality, and time reduction.
And, preferments/levains are the most efficient vehicle for accomplishing the above.
--Pamela
...an excellent post - as usual. I always enjoy your insights.
SF
Hi,
I expect the reason to use it at the "peak" of ripeness, is that this is when the maximum number of yeast organisms are in the starter.
With that said, I'm very lax about how much starter I chuck in (I often measure flour/water in a levain build, but approximate the starter). Also, my levain builds rarely use starter at it's peak. If my starter has been hanging around in the fridge too long, I usually just increase the amount of starter. This doesn't seem to affect my final product. But, then, I haven't been scientific about testing it.
My two cents worth...
MommaT
As I understand yeast, from my beer brewing experience, it is an organism that metabolizes food aerobically when there is oxygen present, and anaerobically when the oxygen is all used up. In both cases yeast produces carbon dioxide, but during aerobic fermentation hardly any alchohol is produced. However, yeast makes more of itself (multiples faster) during aerobic fermentation. Yeast production peaks just as the oxygen reaches depletion.
At this peak when the density of yeast cells per liter of liqud is greatest--it's called "krausen" in brewing; I think that's German for "crown"--a portion of the yeast is drawn off, and added to new wort--the sugar water that becomes beer--to start it fermenting. In the new environment the yeast cells encounter a fresh supply of oxygen, and continue multiplying at the aerobic rate. Thus the new wort starts fermenting vigorously, and the fermenting wort that contributed the peak density yeast begins to slow down, the crown deflates (anaerobic fermentation) and alcohol production increases.
Now back to bread: I think the analogous thing happens in bread, but I've never read a book that confirms it. When a levain (or sourdough starter, or polish, or biga, or whatever) is fed new flour--and maybe sugar too--mixed with water, it encounters an oxygen rich environment and reproduces like rabbits giving off lots of carbon-dioxide.
The key is to introduce the maximum number of viable yeast cells (highest density) to our flour, water, and salt mixtures. (analogous to the wort in brewing) so we get vigorous rises. That peak in brewing is visable in the thick layer of foam that forms on the top of fermenting wort: the "crown". Analogously, the maximum yeast density of our levain is visible in its bubbles and its expansion. (It would also suggest that "old dough" really can't be very old. In bakery practice, it's usually only one day old, after which the rate of yeast cell production in the old dough is exceeded by yeast cell death; i.e., its past its peak.)
I think my analogy is correct, but I'm neither a beer nor bread scientist, merely a homebrewer, and a homebaker (and, of course, a consumer of the best of both). I welcome correction from the more expert.
David
Great discussion! I think the upshot of all this is, if you use your levain at less than optimal strength, you have less yeast to do the work. So, what happens when you make a loaf with only a little bit of yeast? It may eventually replicate enough to raise the dough but it will take a long time and the flavor will be very different from what you have in mind since the other beasties are also multiplying. Sour bricks.
It's more than the yeast that we're after here. We need the acidity too which affects the final dough's extensibility (gluten development) and flavor.
--Pamela
Hi clazar123, the difference I've found is only in the time to rise. The sour flavour is vritually nil for a quick rise but great for a slow rise, irrespective of the starter potency. i.e. my starter, when well fed and vibrant, rises the SD faster but produces little if any sour flavour. Conversely, my starter when it has not been fed for a few days, simply takes longer, thats all. But the flavour for my long fermentation and rise, is much better the longer it takes.
I always prefer flavour over speed, now that I know the difference, and I only feed my starter to keep it reasonably active, and I am no longer concerned about trying to attain the absolute peak of health for it all the time.
I guess my real point is, I'm having a hard time believing all the talk about keeping a SD starter in peak health. Seems to me to be a waste of time and flour. My best SD loaves are when I use very, very little starter and therefore use a very long fermentation ( 2-3 days) in cool conditions. Wow, what great flavour !
I'm speaking ONLY of my own experiences here, having not tried other commercially available starters. My starter is one that I began 2 months sgo with nothing more than flour and water.... I fully accept that others may find different results and therfore for them a different starter feeding regime may indeed be required.
Paul.