Chas,

I found what I was looking for--at

http://www.dclyeast.co.uk/DCL_Main/main_tech/tech_dried.htm. The important part of the material at that site that relates to how much yeast (active dry yeast, or ADY) to use is the following, which I have excerpted:

*The quantity needed is mainly determined by the recipe and process used and on local climatic conditions. As a guide, when processing a dough at 27°C (80°F) the quantity in grams of Active Dried Yeast required per 100kg of flour is indicated approximately by dividing a factor 1360 by the number of hours of bulk fermentation.*It takes a little work to convert the above to your situation, but let’s give it a try. For purposes of what follows, I will assume that you plan to use 1 kilogram (1000 grams, or 2.2 pounds) of flour, and that you would like to use compressed (cake) yeast and a room temperature of 65 degrees F and a 5 hour fermentation.

Based on the foregoing assumptions, the amount of ADY that would be needed for 1 kilogram of flour would be 1360/(5 x 100), or 2.72 grams. Since the above excerpt is based on ADY, to convert to cake yeast, we have to multiply 2.72 grams by 2. That gives us 5.44 grams. To convert that quantity to ounces, we divide it by 28.35, which gives us 0.1918871 ounces. From this point forward, I will give you the exact numbers in case you want to follow on your own calculator.

The above excerpt is also based on a fermentation temperature of 80 degrees F. To convert from that temperature to 65 degrees F, perhaps the easiest way is to adjust the amount of cake yeast. As chiguy has mentioned, for every 18 degrees increase in dough temperature, the rate of fermentation doubles. The number I usually use is 15 degrees, which is what General Mills uses, and I will use it here simply because it makes the math easier, especially since the difference between 65 degrees and 80 degrees happens to work out to exactly 15 degrees. To equate the two situations, if we double the amount of yeast, we get 0.3837742 ounces. Since one of those little cubes of fresh yeast found in the supermarket weighs 0.6 ounces, 0.3837742 ounces represents about 5/8 of one of such cubes. That sounds plausible to me.

If we use your 15-hour fermentation time example, you can go through the same exercise as above, or, since 15 hours is 3 times 5 hours, you can simply take 1/3 of 0.3837742, or 0.1279247 ounces of cake yeast. That comes to about 1/5 of one of the small supermarket cubes of cake yeast. That also seems plausible to me.

To simplify the math further, I have converted all of the above math to a simple expression that will save you a lot of time. Just divide 1.9188712 by T, Where T is the bulk fermentation time. That will give you the ounces of cake yeast you need for the fermentation time T. If you want to know what fraction of one of those little cubes of cake yeast that represents, you simply divide the results from using the expression 1/9188712/T by 0.6. Keep in mind, however, that this expression applies only to using 1 kilogram of flour, cake yeast, and a 65-degree room temperature fermentation. If you change any one or more of these parameters, the expression has to be redone. I think I gave you enough of the math and methodology to allow you to redo the expression yourself, but if you need help, let me know.

I have no idea how well the above expression will work in your real life situation. The final calculation is a guide only and there are too many variables at work that can alter the outcome, and the scaling process I went through may introduce its own effects. The above expression eliminates some of the variables but there are others at work also. For example, for Neapolitan style pizza dough, salt is often used as a regulator of the fermentation process, and water temperature can also be used to alter the fermentation process. Even changing the hydration can affect the rate of fermentation. Neapolitan doughs quite often use a lot of salt, in many cases from about 2.5-3% (by weight of flour). This can slow down the normal rate of fermentation. So you may want to increase the calculated yeast quantity a bit since I suspect that the material excerpted above does not contemplate such high amounts of salt. You might also use a water temperature to provide a finished dough temperature of around 80 degrees F. Beyond that, you will have to do some experimentation to get the dough exactly as you want. Like it or not, experimentation is inevitable.

Please let us know if you decide to proceed based on the above and, in particular, what results you get.

Peter