Bread Dough Fermentation

Fermentation, at it's core, is all about yeast. Yeast are a kind of fungus, single-celled and ubiquitous. The key is that there are two processes going on: natural enzymes in the yeast breaking down the large starch molecules into smaller ones and into sugars, and yeast eating the sugars and producing C02 and alcohol. The alcohol produced by the yeast during fermentation—along with a multitude of other reactions—are what give great bread its characteristic flavors and aroma.

But other important things occur during fermentation. For one, the gluten you’ve just formed in kneading starts to relax, while at the same time continuing to form. How does that happen – relaxing and forming? Well, gluten is like a really uptight rubber band. Be rough with it (i.e, knead it), and it gets all tense and persnickity, and toughens up. But if you leave it alone, it calms down and relaxes. Remember what’s happening right now, though: the yeast is producing gases. The network of gluten traps those gases, and slowly gets stretched – like a rubber band. That’s why you need gluten in your bread; without it, those gases would just escape.

Another important thing that happens during fermentation deals with acids that the yeast gives off, lactic and acetic acids, most importantly. Those two are important dough conditioners, or things that make your bread taste better and keep longer. The longer the fermentation, the more time the acids have to act on the dough. Therefore, many experts have determined that for the best possible bread, a long and slow fermentation is best. This often means using less yeast (which will take a longer time to rise the dough), but it can also mean lowering the temperature at which the dough is fermented (which slows the yeast activity, preventing an over-risen dough).

Generally speaking, more fermentation means tastier bread.

Bulk Fermentation

The bulk fermentation for any dough is a crucial step in the bread baking process, even if it isn't the most exciting one. We call it a bulk fermentation because we are letting our dough—the entire batch—ferment as one mass, before dividing and shaping it into loaves. It's during our bulk fermentation that the yeast does the majority of its work, helping our dough gain flavor as ethanol and other byproducts are produced, and gain structure as CO2 inflates our gluten network.

Most breads rise twice: once before loaf formation and once after. With each successive rise of the dough, the yeast gets a little more tired, and the sugars are used up. This results in less and less CO2 production and hence formation of fewer air pockets in the bread. Therefore, the more times the dough must rise before baking (such as with pumpernickel, which requires four rises), the denser the texture of the bread. Letting the dough overrise can kill the yeast (far better to punch it down twice than to let it overrise once).

So, can the bulk rise be slowed down?

Yes. A slower bulk rise will encourage more flavor and structural development up to a point. But remember, the yeast has a limited food supply, and we want to make sure to leave it enough food for a successful final proof, and make sure enough sugars are present to allow our crusts to properly caramelize when we bake them. If you want to let you dough proof for longer, try bulk-fermenting it in a cooler place.

Cold temperatures slow down the yeast process much more than they slow down the enzyme process. So delayed fermentation allows the enzyme reactions to progress much farther before the yeast has made the dough ready for the oven. Encouraging the enzyme reactions like this gives the bread much deeper, more complex flavors. It also provides more sugar for the yeast to do its thing.

All the best breads have historically used some version of this. Soakers, bigga, poolish, starters, old dough techniques, etc. etc. are ways bakers have allowed the enzyme reactions to progress more without the yeast progressing too far. The refrigerator technique is just a simple, modern version.

Pre-Ferment Method

A pre-ferment is what you get when you ferment some of your ingredients for a long time before mixing all the ingredients into the final dough. The world of preferments is vast, each with different flour and water ratios and names. A preferment is essentially a mixture of flour, water, and a leavening agent left to ferment before mixing everything into a final dough. Preferments help bring flavor, aroma, and keeping qualities to your bread. The extra fermentation time contributes additional byproducts of fermentation to your dough in the form of organic acids and alcohols—flavor. You can also use a preferment to skew the populations of lactic acid bacteria (LAB) and wild yeast, which has an effect on taste and texture in the final dough as it in turn ferments.

A pre-ferment can vary wildly in hydration level, from as low as around 50% (twice as much flour as water, by weight), to well over 100% (equal amounts of flour and water, by weight); but generally, a pre-ferment is wetter than the final dough will be.

You can use this method with practically any bread recipe (take some of the flour, mix with some of the water, add a pinch of the yeast, let sit, etc.); but often, you won’t be able to add all of the flour that the original recipe called for. This is because the portion of the flour used for the pre-ferment has soaked up much more liquid, sitting so long, than it would have if you just made a straight dough with the ingredients. In turn, this means that there is less moisture available to hydrate the remaining flour.

Also, a pre-ferment is not an autolyse. An autolyse (ideally, anyway) uses no yeast; a pre-ferment does. In bread baking, autolyse is best described as the hydration rest following initial mixing of only flour and water that occurs before kneading has fully developed the gluten. An autolyse period gives the flour time to soak up all the moisture, resulting in more orderly gluten formation. The actual chemical changes taking place are similar, as a type of fermentation is actually taking place in both; but in a pre-ferment, the yeast begin to act, creating lactic and acetic acids, those crucial dough conditioners that strengthen your gluten and improve the flavor of your bread. In an autolyse, the carbohydrates begin to break down into sugars, and the proteins begin the process of forming gluten.

Bread that has been pre-fermented has the faintest hint of a sourdough flavor, but only so slightly; otherwise, it is deeper and more complex than just usig an autolyse. Just be careful not to over-knead when mixing the final dough.

Biga, poolish and levain are all variants of a preferment, as is pâte fermentée.

See Bread Preferments page for a description of the different types.