Sourdough Sponge Method 
Pre ferments are considered essential in most Artisan bakeries, whether using sourdough starter as the leavening agent, or using regular yeast, or a mixture of both. In previous articles, I've spoken about sponges briefly, but here I'd like to cover the subject in more detail, as applied to using sourdough starter only, without refined yeast.
Why make a sourdough sponge?
A sourdough sponge serves to activate the yeast colonies and microflora contained within a sourdough starter by feeding them in a way that accelerates their natural action. The method which follows can be a bit time consumptive, but the end, as you will see, justifies the means.
To test the effectiveness of the sourdough sponge method, I have, on many occasions, made two doughs from the same recipe at exactly the s ame time, with the same flour and same water temperatures - only with one of them I have made the dough 'straight up', and the other I have made using the sourdough sponge method. I have then refrigerated the doughs in bulk form overnight to proof. and consistently have found that the dough made using the sponge method rises up to 100% more than the 'straight up' dough. In the final proof, the sponged breads rise about 50% faster than the other, regular dough. The bread baked from the 'sponged' dough is also lighter and brighter in colour, with a thinner, crisper crust.
What's involved?
Step one: Hydrate the starter - Sourdough sponges are made by adding the full water component of a recipe (warm water is essential, and this water can be quite warm - I say 'bath warm', but not hot) to the portion of ripe sourdough starter in the recipe, whisking them together thoroughly to aerate and hydrate the starter.
Step two: Feed the sponge - You then whisk into this up to half of the rest of the flour in the recipe. The batter resulting is allowed to stand for long enough to 'sponge', or grow in volume via the production of carbon dioxide bubbles as a result of the accelerated fermentation process.
Step three: Build the dough - When the sponge has grown to about one and a half times its original size, you add the rest of the flour in the recipe, rest the dough till it's grown a bit (or about an hour, though I go on the look of the dough).
Step four: Finish the dough - add the salt (autolyse again!) and work it through the dough.
Step five: Bulk Proof - allow the dough to proof and observe just how much bigger it gets!
Why does the sourdough sponge work?
For the technically minded: A sourdough starter has a simple diet - flour and water. The microbiology of the starter (bacteria and enzymes) acts on the flour to convert it to simple sugars, which are then consumed by the yeasts, giving off bubbles full of C02 as the bi product. These bubbles, wrapped in stretchy glutenous material, are what give the bread it's rise.
What a sponge does, then, is provide the starter with both mechanical (through whisking) and chemical ( food at exactly the right temperature and consistency) help, to make t he leavening process accelerate.
For the non technically minded: A sponge is a bubble bath for starter! Starter has a feast in a sponge...and then multiplies...fast!
Details, tips and tricks
A sourdough sponge can be built over time (which is the best way to do it), or if you're in a hurry, it can be done as a preliminary stage in any recipe.
All you do is start with whatever the liquid measurement is in the recipe, and add the flour gradually, first using a whisk, and later kneading in the flour roughly before letting the dough rest to add in the remainder.
I'll add at this point that once a sponge has begun to bubble, it can be refrigerated for a day or more in a sealed container with the lid ajar, until you are ready to use it. I often keep sponges in the fridge to save time with production runs in my bakery. They recover from the cold very quickly, and actually deepen the flavour of the bread because of the temperature changes involved.
Thin vs thick sponges
Your sponge can be made quite thin and watery, which will cause it to 'come on' quickly - but it will also expire equally quickly, so you need to progress to the dough stage as soon as the water begins to separate from the batter (this will show through the side of a clear plastic container quite clearly).
There should be a lot of bubbles in the batter (or if it's a thin sponge, 'milk')before moving to the dough build - if not, whisk again! A thin sponge can be used as a pre dough process, adding only a few minutes to the process, but making your dough so much better!
A thicker sponge (more flour) will take longer to 'come on', but will also hold for much longer before needing to be used. A thicker sponge won't separate, as it forms a kind of structure which is reasonably stable and which allows the bubbles to continue to multiply easily. A thick sponge will rise much more than a thin one.
Chemical vs mechanical dough development
An even more effective way to build a dough from a sponge is to take it from a thin sponge right through to a dough, in small stages, with plenty of rests between adding small amounts of flour. I have written about this method before, the white sandwich sourdough recipe. However, I've been using this technique in my bakery lately as a way of getting around the fact that we don't have a mixer, and I've found it is remarkably workable for large doughs, up to ten kilos. That's because the resting between stages makes the dough very relaxed. This in turn means that you don't have to work the dough to get the flour to combine.
Chemical development refers to dough development that comes about as a result of the fermentation process which begins to happen the minute flour is introduced to water. It is dramatically accelerated when a fermentation agent (like sourdough starter) goes into the mix.
Mechanical development is basically kneading, whether using a machine (a mixer or bread machine) or just two hands. Mechanical development by hand is not generally as pronounced or as effective as a machine, because we just don't have the power to get it happening using our muscles alone.
However, by building a sponge in stages, you are effectively getting chemical development to do the work without the need for a whole lot of kneading. This suits our purposes very well, and has the added advantage of improving the flavour too.
There are a bunch of other tips and tricks in this section, which are worth checking out.
Tips & Tricks
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