Another question. Seem like a lot of people use cake yeast in these pies. Does it have a different taste than IDY? What are the reasons for using it?
I believe the majority of NP style pizzerias, particularly those that are VPN certified use CY (brewer's or fresh yeast) as I assume that is their standard. I'm not sure how many NY pizzerias use CY but my guess is not many. Perhaps other members will also tell you of their own experience with CY.
I can't recall where I read it (somewhere on the forum no doubt), but there isn't suppose to be much difference in taste between CY and commercial yeast IDY/ADY if any. In my own limited experience, I found there to be a very slight difference in taste with CY having a bit more flavor but very slight difference. I have also noted that when a dough is allowed to ferment out well, CY will produce a slightly drier crumb like SD starters more so that IDY. I have noted that IDY/ADY doughs are more forgiving in this area.
There was a recent thread (http://www.pizzamaking.com/forum/index.php/topic,12948.0.html
)by member Mmmph that documents his test between CY and ADY where he noted a dramatic difference in the rise, flavor, and oven spring. You can also note that Peter states in reply #9, that Cooks Illustrated noted that CY produces the most gas during fermentation. In my limited experiments with CY, I too have noted that it gives great rise, but oven spring is impacted by many other variables as noted in the link Peter provided in reply #9.
When I tried to source CY locally, I called almost a dozen bakeries and only found one place that uses CY and would sell me a block. Great Harvest Bread Co. When I inquired why other bakeries didn't use it, many stated that they found it to be inconsistent compared to commercial yeast.
I have now bought 2 blocks of CY and both gave perceivably different performances. The first block I got must have been contaminated somehow as every time I used it and ate pizza made with it, I always noted a funky yeasty aftertaste in the back of my mouth that would linger for hours. It was very unpleasant. Every batch of dough made from this CY yield the same results. So much so that I questioned other members about this experience to which they had not experience the same. After a long break from CY, I decided to try it again and did not note this strange aftertaste with the 2nd block.
The 2nd potential downside of CY is the question of storage vs viability of the CY and issue of waste. Member dellavechia has noted that he has refrigerated CY for upto a month and noted no change in leavening strength. Other members have frozened and thawed CY without issue. I have had mold develop on the CY after 2-3 weeks of refrigeration in a ziplock bag. It definitely doesn't keep as easily as ADY/IDY.
CY is cheap at only a few dollars a 1 lb. block but I just don't like the idea of tossing the majority of it as I don't make enough pizza or bread to use it up. I have recently made an experimental starter from CY to avoid having to buy "fresh" CY each time and to avoid having to throw away the excess. This way I can always have relatively fresh "cake" yeast on hand, have it perform consisently without the worry of contamination or getting a different strength of CY, and avoid waste.