Check out this:
http://www.probrewer.com/library/archives/quality-control-in-the-brewery/
Dr. Michael J. Lewis wrote in that article:
Generally, brewers are well aware of the need for specification and consistency (quality) in the brewhouse operations. That might be said with less confidence in cellar management in wort aeration, fermentation temperature, and so on and there is one glaring shortcoming in many breweries that is worth mentioning: control of the yeast pitching rate.
Michael J. Lewis, Ph.D., is professor emeritus of brewing science at the University of California, Davis, and the academic director and lead instructor of UC Davis Extensions Professional Brewing Programs. Lewis has been honored with the Master Brewers Association of the Americas Award of Merit and the Brewers Associations Recognition Award. He is an elected fellow of the Institute of Brewing & Distilling. He is also a recipient of the UC Davis Distinguished Teaching Award.
If it's good enough for him it's good enough for me.