low hydration + cool starter index
Yeast vs LAB lag phase (may be relevant to Desem starter optimization)
Debra Wink writes:
Reducing sourness can be accomplished by shortening the refreshment cycle, not because of aerobic vs anaerobic, but rather by taking advantage of the disparity in lag phases between yeast and lactic acid bacteria (LAB). Bacteria reproduce faster than yeast, but yeast have a shorter lag phase. The lag phase is that time between refreshment and the start of population growth (reproduction). The organisms need a little time to sense their environment and re-orient themselves to the change that refreshment brings (pH, nutrients, waste products, etc.) before they begin growing again. For LAB it takes longer, so yeast start growing first. Each time you feed, it starts a new lag period. If you stop the refreshment cycle short, so as to keep the LAB from taking off, you give the yeast a little advantage in the race by cutting the LAB off at the knees.
You can't completely eliminate LAB, but you can reduce the sour by cutting their numbers.
While I'm sure LAB do encounter longer lag times compared to yeast, bear in mind that the higher the inoculum the shorter the lag..
I did find a paper that looked at the cell numbers of LAB and yeast during the refresh cycles of lievito madre done for panettone production. The starting ratio from storage was 10:1 (LAB:yeast). After each of the short-time (4 hours) refreshes the ratio shifted towards 100:1 (LAB:yeast). So based on that evidence this high inoculum (small feed) and short duration didn't favour yeast at all, it favoured LAB.
Feeding this way cuts back on acid, that's what it really does. LAB have no problem holding their own and will typically always outnumber the yeasts.
100:1 is a standard and stable ratio.
Liquid vs firm sourdough:
Debra Wink writes:
So, why does my firm starter produce milder bread than my liquid one, when firm starters have a higher percentage of acetic acid? Because it has a lower total acid concentration. More specifically, the bacteria grow slower in a dry starter, so their population shrinks over multiple refreshments (yeast seem to hold their own).
Debra Wink writes:
In general, when baking with 100% whole wheat, what % of the total flour do you try to pre-ferment
In general I don't care for sourdough's acidity in whole wheat breads, so I don't make them. I tried desem for a while, and it was milder, but I wasn't loving what, to me, seemed like a strange flavor. The things that promote mildness, aside from keeping the starter at cave temps like desem, is keeping it very stiff, feeding 3 times a day leading up to mixing your dough, use as little prefermented flour as will do the trick (11-18% probably), and try to get it from mixer to oven in about 6 hours or so. There are a lot of enzymes in whole wheat, and they will break down the dough if you take fermentation out too long. But this varies a lot from one brand/type ww flour to the next, so you just have to experiment.
Population dynamics http://www.thefreshloaf.com/comment/95232#comment-95232
Debra Wink writes:
By "strength," in this context, I think what we're really talking about is the collective power of the yeast to huff, and to puff, and to blow the bread up :-) In other words, a strong rise, or rising power. It is the yeast fraction in the culture that provides the lift. Lactic acid bacteria (LAB) could raise dough in theory, but in practice, they fall flat. So, a good rise is all about healthy, vigorous yeast. Bacteria contribute acids which flavor dough, but also play a big part in gluten structure and rheology. In the short term acid tightens gluten, contributing to dough strength, but in the long term, it accelerates proteolysis, contributing to its breakdown. And it adds sourness that is not welcome in all breads. You'll find yeast/lift at one end of the starter spectrum and bacteria/sourness at the other. You can't maximize both at the same time; one comes at the expense of the other. Where you want your starter to be on the spectrum, depends on the bread you are making. For panettone and pandoro, it sounds like maximizing lift, and minimizing sour is the goal.
I think the key to understanding starters, is to recognize that population dynamicsand metabolic effects are two separate, albeit related issues. Population dynamics have to do with organism numbers, and how they interact and fluctuate in relation to each other and to their starter environment. Whereas metabolism is about what those organisms aredoing, and what effect that has on the dough. The magnitude of those effects are related to the population numbers. But the numbers are regulated largely by how hospitable the sourdough environment is to the various species, and how much antagonism there is between them. Does that make sense so far?
Dan gave us a good overview of howdoughis affected by hydration (some cereal chemistry as well as metabolic effects), but now let's take a look at how thecultureis affected---the population dynamics---because that will determine themagnitudeof the metabolic effects. Lowering hydration will slow all the microorganisms, yes, but yeasts are not quite as sensitive to it as the lactobacilli. In other words, the growth rate of the bacteria declines more sharply than that of the yeasts. Sourdough LAB thrive in warmth at high hydrations; low hydration and cool temperatures really slow them down. Yeast benefit from this, because they have less competition from the bacteria, so they have more space, and the resources to expand. They aren't quite as hindered by low hydration, low temperature, low pH, salinity, etc., as lactobacilli are, so even if they do slow some, they gain an edge because the bacteria are slowed more. And the one thing that yeast are more sensitive to than lactobacilli---acetic acid---is reduced as the bacterial population shrinks. So, when you knock back the bacteria, yeast tend to flourish, and rising power increases as sourness decreases.
But the key to it all, is multiple refreshments. It's the regular dilution through feeding that shrinks the bacterial population here, because they aren't keeping pace with the yeast, relatively speaking (and starter ripeness, and readiness for feeding is determined by yeast rise and fall). Because it takes some time for the populations to change and re-stabilize, a starter maintained firm (and fed frequently) for at least a week is probably going to give you better results in your panettone than a liquid starter, even one that is firmed up "as needed." It's the difference between a true firm starter, and a firm pre-ferment. The effect will be different, because the populations are different. In a firm culture, you are actually manipulating the starter environment to suppress bacteria (sour) and enhance yeast (lift), whereas a firm pre-ferment is more about manipulating the metabolic effects to increase acetic acid. See the difference? A culture maintained firm will give you less sour (and more lift). A firm pre-ferment made from a liquid starter may give you more. The magnitude of the metabolic effects reflect the relative differences in population numbers.
Generally speaking, a high inoculum will favour a more lactic flavour while a small one will open the door for more acetic acetic development.
Q: How do I judge maturity of a low hydration (e.g. 50%) whole grain starter as used in Desem, and what is an optimal maintenance schedule?
Open crumb w/ 100% spelt bread: