This makes enough for my baguette recipe, but of course it can be increased if need be for some other application. The amount of yeast employed in a poolish is tiny relative to the flour and water. So tiny, in fact, that for a poolish sponge this small, we'll need to dissolve some instant yeast in water, then administer the solution in spoonfuls. Start by combining:

2 ounces water
1/8 teaspoon instant yeast

...in a small bowl.

Stir until the yeast is completely dissolved:

Fetch a slightly larger bowl, and put in it:

4 ounces all-purpose flour

plus

2 teaspoons of the yeast solution

Pour in:

4 ounces of water:

And stir with a fork until it's all combined into a batter.

Cover with plastic wrap and leave it at room temperature for 12-16 hours until it looks about like so:

Nice and bubbly, yes? That's what you want. And there you have it: one poolish. This will keep well in the fridge for two days.

Pâte fermenté isn't the be-all and end-all of sponges, you know. The poolish occupies its own special place in the preferment firmament, right next to the Italian biga (but we'll talk more about that some other time).

You'll recall in my opening remarks about baguettes that, in addition to various technologies like the deck oven, the pre-industrial French lacked the techniques required to produce fast-rising breads. One of the most important of these techniques was invented by the Poles, themselves no slouches at baking, and who were in fact — at least in matters of bread — at least equal to the Viennese. For they discovered that by adding a small amount of brewer's yeast to a slurry of flour and water, a very flavorful — yet still relatively fast-rising — goop was created, one that could be added to fluffy fine breads to increase their complexity.

What kind of sponge is this? French bakers asked their Viennese teachers (who'd been employing the Polish preferment for decades by the mid-1800's).

Polnisch.

What kind?

Polnisch.

Poolish?

Ja, right, poolish...whatever.

And that's how it's been referred to in France (and pretty much everywhere else) ever since.

It's really just bread dough, only you don't bake it. Of course, if you make bread regularly enough you can just make a little extra dough and hold it in reserve for the next batch. Pâte fermentée will keep for 3 days in the fridge and about 3 months in the freezer. A basic formula is:

10 ounces bread flour
3/4 teaspoon salt
1/2 teaspoon instant yeast
6 ounces (or slightly more) water

Combine your dry ingredients in the bowl of a mixer with the paddle attached.

Turn the mixer on low and stir for a few seconds, the add the water and stir for about 30 seconds until all the ingredients are moistened.

Switch to the dough hook and knead for five minutes. You want a firm and slightly tacky dough.

Put the dough into a bowl and cover it with plastic wrap.

Let it ferment at room temperature for an hour, until it's increased in size noticeably.

The put it into the fridge overnight. The next day — presto chango — you'll have made pâte fermentée. Use it right away, within 3 days, or freeze.

Pâte fermentée is what we in the English-speaking world call "old dough", even though it means something closer to "fermented" or "ripened" dough in French. Classically, the old dough technique is very simple. Every time a baker makes a batch of baguettes (or some other bread that might be improved by old dough) he or she simple reserves a piece of the unbaked dough and stashes it away for use the next day.

Over the course of the night some very interesting things happen. Yeasts continue to reproduce, creating alcohols (and as those of you who've read other posts of mine on flavor know, some flavor compounds are only "unlocked" by — i.e. will only dissolve in — alcohol). Bacteria grow and create flavorful acids. And enzymes proceed to run amok slicing and dicing long-chain carbohydrate molecules (starches) down into sugars.

All of this is a great boon to a baguette dough (or any other bread dough it's added to), both in terms of flavor and color.

Whenever you're maintaining an active, full-strength starter, you always need to at least double its weight to keep it healthy and happy. That can be a lot of starter assuming you keep it going at room temperature...two ounces makes four ounces make eight ounces make a pound and so on. Do that every day for a week and shortly you'd grow The Blob. Anybody seen Rex?

But what if you want that kind of exponential growth? Say, if you suddenly had a lot of bread you wanted to make, but only had a cup or so of starter to work with? The good news is that an active starter can be refreshed with up to three times its weight in flour-water mix (quadrupled) and still produce a sponge in the same timeframe. The down side is that it won't taste as complex as a starter that's only been doubled in weight.

Why? Because your average yeast grows a lot faster than your average lactic acid bacteria. Since those bacteria are what are responsible for much of the flavor in a starter, you'll get a very mild-tasting bread. That can be a good thing of course. Many bakers manipulate their starters in just this way to produce either very sour or not-at-all-sour breads by "natural" means.

What do I do if my starter won't grow?

It happens sometimes. You use distilled water, you feed regularly, but you can't seem to reach that ultra-bubbly critical mass. As long as it looks good, smells good and you're seeing at least a few pea-sized bubbles every day, you're probably on the right track. The way to kick a stubbornly slow starter-to-be in the proverbial can is to bump up the feeding schedule, at least for a few days. Instead of feeding it once, feed it twice, morning and night. Odds are after your second accelerated feeding you'll see twice as many bubbles as the day before, and twice as many again the next day. Within 3-4 days you should at last have a full-strength starter.

One of the big variables in the world of bread starter recipes is moisture. Some can be extremely wet, up to 60% water, others somewhat dry, in the realm of 35% water. Is there any practical difference between them?

For the purpose of getting a starter culture going, the answer is no. Though I've had better luck in my starter-making career with wetter starters (as I said, I prefer a 50-50 mix of water and flour by weight). However once you've got your starter going, the degree of moisture will affect taste.

How so? Well, while any starter you make at home will contain the same mix of microbes (and there can be dozens, even hundreds), the degree of hydration will affect their proportion. Some types of micro-life prefer a wetter environment, some a drier one.

Among bacteria, the prime movers behind a sourdough starter's flavor, it's been found that acetic acid producers tend to like things on the dry side, lactic acid producers prefer things wet. That said, if you like a tangier bread (which is what more acetic acid will get you) you probably want to keep your starter — as well as your finished dough — drier. If a mellower flavor is more your thing, keep the moisture high.

Of course all sorts of factors from hydration to storage temperature to the rate of feeding can have an impact on a starter's flavor. Which is why I suggest lots of experimentation.

If you're wondering what I meant when I said that I generally let my starter ferment for five days to make sure I "clear all the suckers out" it's because starter bowls can occasionally grow some funky stuff. Actually, maybe I should take part of that back. They always grow some funky stuff, but occasionally some funky something-or-other comes to dominate the microbial culture. Here in the Ohio Valley, that something-or-other is frequently a bug by the name of clostridium perfringens.

This bacterium is a food pathogen, one that can, has, and does make people sick, sometimes seriously so. This however doesn't stop some people (mostly hill folk) from raising their bread with it. Why? Because unlike just about every other microbe that can grow in a starter bowl other than yeast, C. perfringens creates quite a lot of CO2 as a by-product of its metabolism. In fact the rise you get from it is every bit as good, maybe even better, than actual yeast. People have thus made bread with it for hundreds of years, relying on the heat of the oven to kill the bacteria, making the bread safe to eat. This type of bread is called salt rising bread, and it still has its fair share of adherents, even here in Louisville.

It don't care for the cheesy flavor of salt rising bread, but I'm even less enthused about having a culture of a microbe like that in my kitchen. Therefore, when it happens, I simply wait it out. The telltale sign of C. perfringens contamination is the smell. The critter produces an awful lot of butyric acid as it feeds, and that particular compound, as longtime readers of joepastry.com know, smells like vomit. Yet the thing about C. perfringens is that it can't survive for very long in a high-acid environment. After 36 hours or so it peters out, paving the way for other bugs that can survive in a high acid environment, to take over.

Yeasts are among these, not surprisingly. And in fact a tolerance for both acid and alcohol (which they themselves create) is very likely a competitive adaptation. Both are poisons to microbes that would compete with them for food in a wet, sugar-rich environment. Knocking them out of the picture means more food for them and their progeny. The King Kong of these is a type of yeast called Saccharomyces cerevisiae, which, again unsurprisingly, is the yeast most bread and beer is made from. It will ultimately dominate a well-maintained in a starter. Sure there are a few types of lactic acid bacteria that can stand the environment Saccharomyces cerevisiae helps to create, but those aren't harmful to humans and in fact help flavor the bread. Very cool.

That said, it always pays to be careful. If you have a starter that smells rank, even after a week of fermentation, throw it out and start over, this time using bottled water. No sense taking a chance on a several day vacation to your own bathroom if you can help it. A good starters should be pale and uniform in color (not blotchy or dark), responsive to feedings and smell tangy/sour, not horrible. Anything that deviates from these general criteria isn't a starter, just a culture, and should be pitched.

That goes for starters that might be well established, but have for some reason fallen off their game. Though Saccharomyces cerevisiae is one bad M.F. microbe, it does happen on occasion that another bug stages a coup. Sometimes when that happens no amount of feedings can tip the balance of the starter back in your favor. Again, throw it out and start over.

Growing your own starter is an elementary project than can become complicated if your water is compromised in any way. If you're connected to a municipal water supply that's heavy on chlorine, for example, or if you have a water softener. On the other extreme a relatively "dirty" water supply can introduce organisms that will out-compete your yeast and prevent a sturdy culture from developing. Here at the pastry house we have a water softener, which rules out the kitchen tap. I therefore use distilled water in a jug. Since feeding your culture with tap water is ideal, if only from a cost standpoint, I'd try one using that first. If nothing happens after four or five days, begin another using the bottled stuff.

Let me begin by apologizing for the photographs in this tutorial. They're a little dark. I do all my starter-tending at night, you see. The light in my kitchen isn't very good, and I have yet to learn how to use my camera under such conditions without the flash (the glare from which I really don't like). So...you'll have to bear with me until I consult my Nikon owner's manual.

The thing about starters is, they're incredibly easy. If they weren't human beings would never have invented bread. The trick, if there can be said to be one, is remembering to care for it. The vast majority of starter failures come from forgetting to feed one on a regular basis. If you can do that — and I feed mine, as I said, before I go to bed every night — you won't have any problems.

Begin a starter by creating a mixture of 50% flour and 50% water (by weight). What you'll get is something that looks like pancake batter, only thicker.

All you do now is set a piece of paper towel on top and let it sit for two days. After which time you may be surprised to see not much happening. Mine looked about like so:

Not much going on but a few bubbles. However the yeast were working in there, as you'll see. The best way to tell if it's active is to smell it. It should smell at least a little pungent...like sourdough bread.

Having gotten the beginnings of a yeast culture going, it's time to start feeding it. This is done by "refreshing" your starter with that same 50-50 (by weight) flour-water mixture that you began with. You want to put in at least as much food as there is starter in the container. I frequently put in double the food that it needs for the first several days. Starting with a fresh container I put in three ounces of my starter (I pitch the rest) plus three ounces of water...

...and three ounces of flour.

And stir it up. As the next few days pass you should be seeing a big change in the amount of activity, by which I mean a radical growth-and-contraction of the mixture each night. Here's what mine looked like on the second day of regular feedings (in the middle of the night...what I do for you people):

That's quite a big expansion from a scant nine ounces of mix — the entire quart-size yogurt container is full! This is a full strength, rarin'-to-go starter of the kind you can bake with. And while I could bake with this, I usually wait for a full five or so days before I use it, just to make sure I've cleared out all the suckers (i.e. potentially harmful bacteria).

This is what the starter typically looks like in the morning once it's exhausted its food supply: collapsed.

What's happening here is that the yeast have reached their peak population, and lacking any more fuel to keep growing, are lapsing into a kind of semi-dormancy. A starter that looks like this should still, however, be considered a full-strength leavener. A few hours from now and the starter will have returned to a mostly placid, bubble-less mass, not unlike the second photo above. At that point it'll need to be refreshed to get its bread-raising zip back.

Having created a starter, you can simply keep it out all the time, refreshing it nightly. That, however, can get tiresome unless you're using one several times each week (it's also rather wasteful considering how much starter you'll be throwing away every night). The way to store it is to give it a fresh infusion of food, let it sit for half an hour or so, then put it in the fridge. Fed a minimum of once a week, it'll stay active indefinitely. I generally keep the same nine-ounce quantity in the fridge, since it doesn't take much to feed and I know I can build it up to whatever I need in one or two days' time.