Norma,
Today I did several forum searches of my posts using the terms "blister", "blisters" and "blistering". I then studied the posts to get an idea as to how blistering factored into my pizzas. When I was done, I concluded that the single factor that was consistent through all of my pizzas where I talked about blistering in my posts was a long fermentation. The long fermentation was as a result of using a small amount of yeast and a long, cold fermentation, or using a larger amount of yeast but where the dough was in effect on the cusp of overfermenting. The latter was fairly rare for me since I was not a user of large amounts of yeast for my doughs. However, in my next post, I will talk a bit about frozen doughs using large amounts of yeast and where blistering did occur when defrosted and used to make pizzas.
Some of the best examples of cases where I used a small amount of yeast and long fermentations are in the thread at
http://www.pizzamaking.com/forum/index.php/topic,3985.0.html. In that thread, I discussed six different pizzas where the duration of cold fermentation was in the range of about six days to 23 days. I specifically mentioned the blistering phenomenon in those six cases although I wish I had done a better job showing the blistering in the photos I posted. The specific posts are Reply 23 (10 days plus 4 1/2 hours of cold fermentation), Reply 29 (12 days and 4 1/2 hours), Reply 35 (6 1/3 days), Reply 91 (7 days), Reply 110 (15 days), Reply 117 (23 days) and Reply 123 (12 days). What is significant about these pizzas was the fact that they all used the same basic dough formulation (a basic Lehmann NY style dough formulation), with just flour, water, yeast (IDY or ADY) and oil (and no sugar). However, I did try a few different flours and I tweaked the amount of yeast but not in a way that would have affected the results I was trying to achieve, namely, long dough lives. Also, as a significant departure from the way that most people use yeast in forming their doughs, in my case I used both IDY and ADY (in dry form) late in the dough making process. This was done intentionally to ensure a long cold fermentation window. But while this result was achieved, it could not be said that the late addition of the IDY or ADY "caused" the blistering, at least not directly, and especially since we all know that blistering can occur where the yeast is used in its normal manner.
I also studied my posts to see if I could draw a line as to when blistering is likely to occur. In my case, I would put that line at about three days of cold fermentation. For example, in the Boardwalk thread, I entered at least three posts where I discussed blistering, and the duration of the cold fermentation was about three days in each case. The relevant posts are at Replies 204, 301 and 307.
I also looked for examples of posts where blistering occurred in my pizzas below three days of cold fermentation. I could not find any although as noted above my doughs usually did not use a lot of yeast as to promote rapid fermentation, up to an including overfermentation or something just shy of it. I also cannot recall any case where an emergency dough that I made led to a crust with detectable blistering. Maybe they were there but I did not notice them because I was looking for something else. I think a good thread on the minimal window of fermentation to get blistering is Chau's thread at
http://www.pizzamaking.com/forum/index.php/topic,10656.0.html. As I reread that thread, I found myself nodding in agreement several times.
I think it is also important to point out several things that I did not do with my doughs that exhibited blistering. For example, I did not spray or coat the rims of skins with oil before dressing. I did coat dough balls with oil but not the rims. I also did not let the skins become dry. My practice was to cover a tempering dough ball or a skin made therefrom with plastic wrap. I also did not use any bromated flours. I also did not detect a correlation between hydration value and the occurrence of blistering. I was able to achieve it with hydration values of around 65% and around 50% and values in between.
So, my conclusion is that the predominant factor in the creation of blistering is prolonged fermentation, however achieved. It is also possible that the bake environment and bake temperatures may be implicated in the blistering phenomenon but in my case I used only my standard, builders grade electric home oven. However, I would think that a high bake temperature is better for creating blisters than low bake temperatures.
Peter
