On Prefermented Flour
In last week’s post about what goes into a well-written bread recipe (How to Read a Bread Recipe), I mentioned that one key section was the breakdown of the levain and prefermented flour percentages:
This describes the weight of the levain (5% relative to the total weight of flour) and the amount of flour in the recipe that is in the levain (2.5%, because this levain is 100% hydration or 50/50 flour and water.) This tells you a lot about the fermentation strategy being used and possibly about the flavor of the bread (more prefermented flour generally means more acidity).
I wanted to go into this part of a bread recipe in more detail, since it is where all sourdough breads (as well as many yeasted breads) begin their lives.
It’s probably simplest to first talk about recipes without preferments, aka “straight doughs.” A straight dough is a yeasted dough in which all of the yeast and all of the flour get combined from the get-go. In other words, none of the flour is fermented ahead of the formation of the final dough. Generally this means a shorter overall duration of fermentation, though this isn’t always the case: One can stretch out the fermentation of a final dough by starting with a small amount of yeast (as in most “no-knead” recipes) and/or by reducing the temperature of the dough (aka “cold-proofing”).
A sourdough is never classified as a straight dough, because by definition some of the flour has been prefermented in the levain. No-knead recipes like The Loaf are as close as sourdoughs come to being straight doughs, since the amount of flour in the levain is a fractional amount of the total.
Anything other than a straight dough is by definition “pre”-fermented to some degree, and the portion of the dough that is fermented ahead of the final dough is called the preferment.
Preferments go by a variety of names: biga, sponge, poolish, paté fermentée, etc.:
Biga and sponge are generic terms for yeasted preferments and don’t say anything specific about their composition.
A poolish is a yeasted, “liquid” preferment, meaning it contains a 1:1 ratio of flour to water.
A paté fermentée (aka “old dough”) is either a portion of a previous batch of dough that is saved and used to start a subsequent one, or it is a stiff preferment with a similar ratio of flour and water as the final dough and—unlike all other preferments—contains salt. If it is the former, then it is generally only a few “generations” old, since commercial yeast cannot be propagated indefinitely—any “old dough” starter that gets used over and over again is by definition a sourdough. If it is the latter, it is a lower-hydration version of a poolish, and may or may not include salt.
A recent innovation in yeasted preferments is a sweet, stiff starter, a preferment that is low in hydration and contains sugar, which has magical properties in this context. We will explore this one in more detail in an upcoming guest recipe from Chin Lin Gan, aka @tumblinbumblincrumblincookie.
Sourdough/sourdough starter/levain, etc. are all names for a sourdough preferment. While they all specify the presence of a sourdough culture, these names don’t say anything about its flour and water content. (Just like yeasted preferments, you can have “liquid” or “stiff” levains. And—though it is rare—you could use a sourdough “old dough” method.)
Why preferment flour?
There are three main benefits to using a preferment in bread doughs:
Improved flavor. Longer fermentation means the production of more of the “side” products of fermentation (aside from CO2 and ethanol), especially organic acids like lactic and acetic acid, that give bread tang, and esters, which lend bread “fruity” aromas. Using a preferment adds these flavors to a bread dough, not unlike adding other flavorings in the form of spices or herbs. The amount of prefermented flour and the length of time the preferment proofs determine how much of that flavor the preferment supplies.
Better (or more easily-achieved) structure. The acids produced during (pre)fermentation strengthen gluten bonds; and gluten structure forms passively as a dough sits. Thus a final dough that contains a high proportion of prefermented flour has a leg up in structure formation, requiring less mixing or folding during the bulk proof. (In a sense, a preferment is also “pre-kneaded.”)
Better keeping qualities. Acidity in breads helps fend off staling. All else being equal, yeasted breads with preferments stay fresh longer than those without them. And sourdoughs stay fresh longer than nearly all yeasted breads, for the same reason.
Leavening. While many yeasted, preferment-containing breads include additional yeast in the final dough, all of the yeast could be contained in the preferment. In a sense, a preferment “grows” yeast (and bacteria, in the case of a sourdough) to leaven the final loaf.
Convenience and efficiency for the professional baker. While this is less relevant for the home baker, using preferments in a bakery allows a baker to save time, because a) a simple, single batch of preferment can be divided and used to produce multiple different products, and b) compared to final doughs, preferments are quickly and easily made, so a bread’s final fermentation can happen quickly, without compromising on the benefits of long fermentation.
How much flour should you preferment?
The answer is it depends. Preferment too little of the flour in a final dough, and you don’t really get any of the benefits it might provide. Use too much and you risk the dough being too acidic, which could compromise both the bread’s flavor and its structure (acid strengthens gluten up to a point, a point beyond which gluten begins to fall apart). For this reason, most recipes preferment between 5% and 25% of the total flour.
There are outliers. Rye breads, lacking gluten, require high acidity for structure, so they often contain a high percentage (40-60%) of prefermented flour. Breads with a high percentage of prefermented flour usually get a much shorter final fermentation, to avoid the overproduction of acidity.
What about my recipes?
With sourdoughs, I tend to use two ranges:
0.5 to 5% prefermented flour (or from 1 to 10% 100%-hydration levain) for long-fermented no-knead breads
10 to 20% prefermented flour (or 20 to 40% 100%-hydration levain) for “classic sourdoughs”
I usually decide how much to use depending upon the time of year/ambient temperatures: more in winter, less in summer. The goal is always to get the doughs to proof at similar rates, no matter what ambient temperature they are made under. The difference in flavor between breads from either end of the range tends to be minimal.
For yeasted breads, I actually rarely use preferments, because I prefer to cold-ferment my shaped loaves (and dough balls for flatbreads), since that approach is convenient for me, and the benefits are comparable. (It’s usually redundant to use both a preferment and a long final proof.)
I hope this serves as a useful, if brief introduction to the ins-and-outs of preferments. If you have remaining questions on this topic, please let me know in the comments below.