DaveK,
That’s a great question. Once in a blue moon, I will find an article on the Internet that tries to address the problem of converting commercial yeast in a dough recipe to a natural starter or preferment. An example of such an article, which I bookmarked in case someone raised the question again, is this one:
http://www.nyx.net/~dgreenw/howdoiconvertyeastbreadrec.html. Unfortunately, there is no easy answer to your question, although the referenced article does provide some rough guidelines that one might use to convert a dough recipe using commercial yeast to one using a natural starter or preferment.
As a practical matter, to address the conversion matter one has to first determine how much yeast is used in the original recipe and then try to come up with a percent of starter or preferment to use in place of the yeast called for in the original recipe. If the formula yeast is high, then one might use a preferment at a rate of 15% or more (as a percent of the formula flour). If the amount of formula yeast is exceedingly high, then the preferment percent might be as high as 40% or more (of the weight of formula flour). At those rates, the preferments will act as leavening agents but they will also confer other features and attributes to the dough and finished crust. If the formula yeast is low, then one might use a preferment at a much lower rate. For example, in Naples, the preferment, or starter, is measured in relation to the weight of the formula water, not the weight of flour as is done in the U.S. A typical range might be 1-5% of the formula water. In that case, the starter will be used almost exclusively for leavening purposes. Notably, there are only a few places (two?) in Naples that use natural preferments and, to the best of the collective knowledge of our members, only two in the entire U.S. That is why most of the Neapolitan dough recipes you will see call for commercial yeast (usually fresh yeast), including the recipes for which I provided links in my last post.
If I were to attempt to convert one of the recipes I referenced in my last post, or even the one used by Marioama_1, to use a preferment or starter in lieu of commercial yeast, the way I would proceed would be as follows. First, I would try to convert the recipe to baker’s percents. For reasons to become more readily apparent below, I would calculate the percents of all of the ingredients with respect to the weight of the formula flour, not the weight of water as is typically done in Naples. The key numbers I want to know are the percent of water (formula hydration), which establishes the total hydration of the dough, and the percent of yeast (commercial). Next, I would try to determine the weight of an individual dough ball, if that number is not given anywhere. Fortunately for us, all of the recipes I referenced can be converted to baker’s percents and there is sufficient information to determine a typical dough ball weight (in most cases, the dough ball weight is specified). It is important to note that the weight of a dough ball in all of the referenced recipes will correspond to a particular pizza size and crust thickness to be used with a very high-temperature oven, such as a very high-temperature wood-fired oven. From my experience, for a standard unmodified home oven, it will usually be best to use a smaller pizza size for the same dough ball weight in one of the referenced recipes, or else increase the dough ball weight to allow one to make the size of pizza mentioned in the recipe. This is necessary since a pizza baked in a home oven will not bake the same as in a very high-temperature wood-fired oven.
With the above information, I would then use the preferment dough calculating tool at
http://www.pizzamaking.com/preferment_calculator.html. I would use the dough ball weight option, and enter all of the baker’s percents but for the baker’s percent for the formula yeast. We want to know what the yeast baker’s percent is but only to know if it is a small number or a big number. If it is a big number, then we want to use a large percent for the preferment; if it is a small number, we want to use a small percent for the preferment. This is not a precise process, and there is no table that I am aware of that converts an amount of commercial yeast to a corresponding amount of starter or preferment. To do this, one would also have to specify fermentation times and temperatures, of which there are myriad combinations.
So, for purposes of using the preferment dough calculating tool, we enter a number for the quantity of preferment that bears a relationship to the amount of the commercial yeast called for in the original recipe. Although the tool is based on using baker’s percents in relation to the amount of flour, the preferment itself can be expressed as a percent of the weight of flour, water or total dough weight, whichever number may be given or calculated from the recipe used. Using the preferment quantity number, plus the percent of water used in the preferment itself, the preferment dough calculating tool will provide the ingredient quantities needed to approximate the original dough formulation. However, even if we are successful to this point in coming up with a reliable set of numbers, that doesn’t necessarily mean that we can use the same fermentation times called for in the original recipe. Natural starters and preferments tend to work much more slowly than commercial yeast. So, unless one tries to speed up the process by using a lot more starter or preferment, or take other steps that will speed up the fermentation process, such as using a higher hydration or using warmer water or a higher fermentation temperature, it will usually take longer for the starter or preferment to do its job. Adding some commercial yeast to the formulation, as you postulated in your post, will also have the effect of speeding up the fermentation process, but that will also change the formulation and affect fermentation times. However, if that is something you want to do, the preferment dough calculating tool gives users that option.
I realize that the above all sounds complicated and a lot of work, but if one follows the steps described it should be possible to come up with a workable formulation using a natural starter or preferment in place of commercial yeast. As with any exercise of this nature, it will usually require some experimentation and tweaking of recipes. There are just too many variables when dealing with natural starters. If there is a particular recipe that you would like to play around with, I may be able to give you some guidance as to how you might modify the recipe to use your particular starter. It might help to know what kind starter you are using (e.g., a homemade one or a purchased one) and, if you know, what its percent of water is (or else indicate whether the starter is batter-like or on the stiff side). Please also indicate which specific brand and type of 00 flour you would plan to use, and the type of oven you will be using.
Peter
