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Biga/Poolish/Pate Fermentee - why knead?

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woefulbaker's picture
woefulbaker

Biga/Poolish/Pate Fermentee - why knead?

Hi

Reading Reinhart BBA etc. regarding Biga and Pate Fermentee (not so much Poolish) I noticed that the preparation of these preferments involve kneading and proofing much the same as you would for any final dough.

Since I presume neither gluten nor  trapping carbon dioxide, bulk/volume are major concerns for a preferment, why are these stages of kneading, proofing and degassing necessary in a preferment?   Is this something I also need to do with poolish? (I don't think I've ever successfully had a poolish 'double in volume' btw).

Actually perhaps a bigger question: why use a preferment at all? I'm not sure I follow the logic.  How does it improve flavour (if one presumes flavour comes from extracting all we can from the flour),  if the bulk of the flour used in the final dough has yet to be added?

 

Thanks,

 

Toby

umbreadman's picture
umbreadman

I've kinda wondered similar things about kneading bigas and such for gluten development myself, but I have learned a little bit about them. As I understand it, the reasons for the things you wonder go like this:

For one, the CO2 capturing properties of developed dough are a bit helpful, as they signify the "ripeness" or readiness of whichever preferment you're using. If it didn't rise, it would probably be more difficult to tell when the yeast have reached they're maximum/critical level of activity. By letting it rise/proof, you get a feeling for how active it is by how long it takes to ripen.

Degassing is helpful because supposedly (I forget how it works on a molecular/chemical level at the moment), excessive amounts of CO2 interfere with optimal yeast activity. though, degassing makes a bit more sense in the final dough than in the preferment, I suppose it would still be helpful to ensure the yeast are getting a good, strong start.

The idea of using a preferment to improve flavor comes with the actions of yeast, bacteria, and enzymes in dough, which i won't touch on (unless you're interested). They each contribute in different ways, and having an amount of pre-fermented dough in the final dough increases the initial active proportion of these things. Or to put it another way: Enzymes are present throughout the flour, but useful active yeast/bacteria are introduced by the baker. If you use a small amount of yeast and add it straight to the dough, it is more likely (but not definately certain) the starch-breaking enzymes will overact and dismantle the dough structure before you get a full rise and flavoring from the yeast. If you use a preferment though, you have a larger proportion of yeast and bacteria, as well as "enzymed" flour to begin with, and things will (usually) result in a decent rise by the yeast right in step with good flavor production by all contributors.

I hope that helps; if you want to know more I'm sure people will be eager to add. I'm pretty sure i got that all right, but if not, hopefully someone can correct it. I also apologize if it's too long; i usually end up explaining a lot.

-Cyrus

JERSK's picture
JERSK

   Biga is a rather stiff preferment,50-60 % hydration, and requires some kneading as it does contribute to the overall gluten structure. This should only take a few minutes of kneading.It is usually used in higher hyration doughs to give them extra strength as well as depth of flavor. Poolish has a high hydration, usually 100%, and is used mostly for depth of flavor. It should double in volume for maximum effect. This can take 12-16 hours. It also must be mixed well for this to happen. A biga takes easily that long and may triple in volume. A poolish should be used ideally when it starts to collapse. Though it is not essential. A biga can hold it's structure for 2-3 days. Pate fermentees are just additions of dough from a previous batch. I don't see why any kneading would be required. They're usually added at the end of your final dough mixing or kneading for deeper flavor. Another option German's use is called "altus brat" or old bread. You just simply add a piece of stale bread that's been softened in water to your dough. This adds some additional flavor and is used quite a bit in rye breads, but can work in any bread. As far as degassing preferments, that would happen any way when you mix it into your dough.

woefulbaker's picture
woefulbaker

Thanks Cyrus, JERSK

That makes sense regarding flavour improvement (although I would like to learn more about what happens on a molecular level - enzymes such as amylase etc.)

If memory serves, Reinhart suggests letting the biga double in volume before degassing and storing in the refrigerator.  I don't understand this step other than perhaps to develop gluten or perhaps ensure the yeast is very active before chilling? BBA doesn't specifically mention any such pre-chill practice for the poolish but one would assume the same room-temp ferment is required? 

 

 

KipperCat's picture
KipperCat

Reinhart's Whole Grain Breads has a good explanation of the enzyme action on the flavor and other properties of bread dough.  Even if you're not ready for the book, you could check it out and read the first 90 pages or so. If you're like me, you won't remember it all after the first reading or 2, but  your overall understanding will be improved.

woefulbaker's picture
woefulbaker

I did a bit of reading around on the subject on the WWW from a variety of sources all with slightly differing explanations (!) but it mostly centred around alpha and beta amylase enzymes (from various sources, not least the yeast) and how they break down starches (which attack starch chains/branched chains in different ways thus releasing different sugars)  The finer points  of amylase action are particularly important in the brewing process although it would seem a lot of it is relevant to bread also.

My somewhat limited grasp of the information led me to conclude that longer, cooler fermentation equals more amylase action (without the yeast immediately further breaking down and gobbling up all the released sugars) - more varied and better sugar/flavour profile.  (I'm guessing it also allows time in sourdough starters/builds for the development of lactobacillus and their acidic byproducts).

 

 

 

umbreadman's picture
umbreadman

I agree than longer times would lead to more amylase activity, but cooling the dough would decrease it as well. Logically, the longer you let it sit, the more work it can do, and also on a molecular level, temperature is defined as molecular movement / kinetic energy, so colder means less breaking of starches. manipulating both can be good to pace bread development to your liking. However, in situations like mashes, increasing amylase activity with higher temps does the same job of sugar release and flavor production much more quickly. So in terms of enzymatic (and most microscopic) action, temperature and activity are directly proportional, meaning temp and time needed to achieve optimum sugar / starch balance are inversely proportional.

In addition to temperature, the fluidity of the environment greatly affects enzyme activity. Enzymes are merely proteins that act based on collisions and have no self-motility, thus they are dependent on their environment to convey them to their next substrate. So, in higher hydration doughs, you get more amylase activity vs stiff doughs because the amylase can bounce around a lot easier.

Mind you this is strictly enzymes I'm talking about. The different ways enzymatic processes can interact with fermentation processes are numerous, e.g. if amylases are allowed to act for a short vs. long time prior to yeast introduction, how the amount of free sugars available to yeast will determine rising / fermentation quality. 

Side note: it's kinda satisfying to know that the things I learned in biology class are helpful in practical, everyday situations. If you want to know anything else, holler.

-Cyrus

woefulbaker's picture
woefulbaker

Thanks Cyrus - that definitely makes sense (amylase proportional to temperature)

Makes me wish I'd stuck with biology in school! 

cmoewes's picture
cmoewes

Isn't a poolish/biga usually prefermanted at a cooler temperature (sometime over a long period in the refrigerator)? I recall reading that when you ferment at a lower temperature you encourage the creation of Ascorbic acid (due to various anerobic activities I think) which is a key ingredient in improved flavor and yeast activity for the final proofing?