My first instinct was that you may not have been weighing out the flour and water. As you know, Big Dave Ostrander has noted on several occasions that a 50-lb. bag of flour weighs just about anything but 50 pounds. However, when I went searching for his comments on the extent of variations of the flour in 50-lb. sacks, I came across your post last year at the Pizza Today bulletin board athttp://www.pizzatoday.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=1&t=000771
where you noted that a 50-lb. bag of flour in your shop can weigh from 47 pounds to 52 pounds (not including the roughly 8 ounces that the empty sack weighs.) Seeing that you weigh the flour and water takes that issue off of the table for purposes of this discussion.
My second thought was that the protein content of your flour may be varying from lot to lot or possibly on some seasonal basis. Tom Lehmann has commented on this little known phenomenon before (regrettably the PMQ Think Tank archives are no longer accessible for me to be able to cite his comments to you) but, as noted by member Trinity, a professional baker, the protein content of flour can vary to the point where more or less water is required in the mixer bowl to compensate (see Replies 12-17 starting at http://www.pizzamaking.com/forum/index.php/topic,3416.msg29094.html#msg29094
). If protein content is an issue, I don’t know how you would know it in advance without technical instrumentation to be able to adapt your processes to the differences in protein content to achieve consistent results. If protein content were a seasonal phenomenon, you might be able to make some adjustments to compensate.
I am also aware that there are seasonal factors such as temperature and humidity that can affect a dough, as pointed out in this article by Tom Lehmann: http://www.pmq.com/mag/2006march/lehmann.php
. Measuring and controlling temperatures as suggested by Tom Lehmann in the article is always a good idea, but that method is not precise and involves many variables in its own right that you may not be able to account for in your processes.
I think it may also be safe to rule out the moisture of the flour as a big problem in your case because, unlike those of us for whom a 50-lb. bag of flour lasts for several months or even longer, you are getting the flour fresh and quickly from the miller/supplier and are using it at a fast clip before exogenous factors can materially affect the performance of the flour.
It occurred to me that using rest period during mixing might improve the hydration of stronger flours but that will also make weaker flours “wetter”, and the rest periods will also affect the finished dough temperature as the dough temperature moves in the direction of the room temperature during the rest periods (assuming you are not varying dough batch sizes, mixer speeds, etc.). Even if rest periods were beneficial, I don’t know how you would know it since there are so few reliable and consistent visual clues with low-hydration doughs on the extent of hydration, as I myself discovered recently when working with low-hydration cracker-style doughs. Again, if there are seasonal factors involved, maybe rest periods could be selectively used.
All things considered, it seems to me that if you are weighing your flour and water and are adjusting water temperature to get a finished dough temperature in the desired range (e.g., 80-85 degrees F), those two steps alone should go a long way to getting consistent results. Whatever other changes might be required would be made in the mixer bowl on a case by case basis without your really knowing what factors are making those adjustments necessary. I agree with DNA Dan that I wouldn’t alter the hydration called for in the recipe you are using. I would try to fix as many variables as possible and deal with the other factors by exception, in the bowl and in the oven if necessary. It seems that that is what you are already doing.
EDIT (1/25/13): Since the link to the above Lehmann article is no longer operative, see the Wayback Machine link to the same article at http://web.archive.org/web/20110405042926/http://pmq.com/mag/2006march/lehmann.php