while the UPN room temp was probably more influenced by the firing of the oven than anything else, I am kind of amused at the thought of Anthony reserving less dough in the summer months for mixing the levain - so perhaps you were more likely to get a pizza at UPN before 'dough ran out' in July than say December. Probably totally untrue but amusing to contemplate nonetheless.
Scott re: poolish
In a situation where final dough fermentation time has to be relatively short (one of the main reasons preferments are used at all) a poolish is one option to help add extensibility to the dough. That's one of the reasons it sometimes gets used in making baguettes. Biga, by contrast, has less protease activity and can be used to s add dough strength - the sort of thing you might need in making high hydration dough (eg ciabatta)
As Pete mentions - one can add salt to a preferment or starter - especially when using room temp. preferments.
Didier Rosada mentions this in the Fall 2002, SFBI newsletter:
In addition to improving bread flavor, salt is
useful in controlling the activity of preferments.
When a preferment, such as poolish or sponge, is maturing too
quickly due to warmer temperatures,adding .2 to .3% salt is just
enough to slow down activity without interfering with aroma.
Just remember that when the quantity of salt in the final dough is
calculated, the amount of salt used in the preferment must be
When a stiff levain is becoming liquid or mushy in the center,this
is a sign of undesirably intense enzyme activity (protease) between
feedings. As little as .1% of salt incorporated during the feeding
of the culture will be enough to noticeably slow down the
protease of the flour and bring your sourdough culture to a
normal consistency—without interfering with the microorganism
activity of the sourdough. "
edit: I'm not sure if it's relevant but I thought perhaps clarificationw was needed between the terms 'preferment' and 'levain'. While a levain is technically a preferment, its main purpose (as the name suggests) is to act as a leavening agent for the dough. On the other hand, a preferment is essentially a 'shortcut' - some percentage of the total flour that has been prefermented to impart various flavour and dough characteristics to the final dough without the need for a long fermentation in the final stages. It's essentially dividing up the total dough fermentation into two stages which can make life easier in a commercial bakery. Additional baker's yeast is usually introduced in the final mixing stage, proportional to the remaining flour to be added. When dealing with 100% sourdough breads/doughs the term levain and preferment can be used roughly interchangeably, since no additional leavening agent is being added in the final dough.
Of course the subtleties and advantages imparted by preferments/levains reach far beyond convenience. They can be used in many different ways. One of the most extreme examples I've come across isthe 'Caramelized Hazelnut Squares' recipe in Advanced Bread and Pastry. As I recall, it used 4 different preferments/levains! I can't find the recipe right now but here's a link to the results:http://www.thefreshloaf.com/node/10593/caramelized-hazelnut-squares