Andrea,
Let me start first with your question about what a natural starter/preferment is. Simply stated, it is a mixture of flour, water and wild (or natural) yeast. If the starter culture is properly maintained and properly fed, it can last for years. When used to leaven pizza dough or to confer other attributes to the dough, such as acidity and strengthening of the dough, there are literally hundreds of biochemical activities and byproducts of fermentation that are produced. These are largely responsible for the flavor, color and texture of the finished crust. By their nature, natural starters/preferments are intended to be long term in nature in terms of their use. Once made, they only need to be fed and otherwise properly maintained.
By contrast, preferments based on using commercial yeast, whether it is fresh yeast (aka cake or compressed yeast), active dry yeast (ADY), or instant dry yeast (IDY), are intended to be short term solutions to improving the flavor and other attributes of finished crusts (or breads). The biochemical activity and byproducts of fermentation are far fewer and far less complex than with natural preferments. This limits their contribution to the flavors, color, aroma and texture of finished crusts.
Some common preferments based on commercial yeast are bigas, poolish, sponge, and old dough. They have different characteristics in terms of flour/water ratios, hydration, yeast quantity, water temperature, and fermentation temperatures and times. Their end applications are also different. For example, poolish is considered a good option for baguettes, sponges are good for sweet breads, and bigas are good for doughs that need strength, like brioche. Depending on the preferment selected, they are typically made and used from about a few hours to about a day (usually at room temperature), or possibly within a few days if refrigerated. They are not regularly fed like natural preferments are. If that were a viable option, then much will have been written on the subject. But I have not seen that in my readings. So that leads me to believe that regularly feeding such preferments, such as a poolish, is either impractical or not viable. However, that shouldn’t discourage you from trying, even if it is to confirm what I have said. But, whatever you do, I think it is best to know what your are trying to achieve and for what purpose. A lot of people just like to throw things together and hope for the best. There is nothing
per se wrong with that, but you can spend forever trying to achieve the desired end results. You also have to ask yourself whether you want your pizza crusts to taste like other baked goods. I once used a biga-like preferment for a NY style pizza and got crust flavors that tasted like a baguette bread. I liked the flavor but not as much in a pizza crust.
Preferments based on using commercial yeast will offer many advantages over using just plain IDY or other form of yeast in straight dough methods. You would have to make a dough that can last several days (from about 8 to 15 days) and still be usable (as I have done) to start to get crust flavors, color and texture that even approach what you can get with natural starters/preferments or even classic preferments.
The old dough method you mentioned is a preferment method. Having written on that topic before, at
http://www.pizzamaking.com/forum/index.php/topic,4764.msg40475.html#msg40475 (Reply 1), I will refer you to that post rather than elaborating on it here. You might also want to take a look at the Pizza Glossary at
http://www.pizzamaking.com/pizza_glossary.html, which defines a lot of the terms used in respect of natural starters/preferments and commercial yeast preferments.
Peter
