From brew to brew, my efficiencies are all over the place. It's driving me nuts. I'm using Beersmith, and knowing your setup's efficiency beforehand comes in handy when creating recipes. Differing efficiencies can significantly alter the end result in relation to what you were expecting.
Here are some examples:
My 1st batch of Altbier, brewed on 11/16/11, had 69.18% brewhouse efficiency.
My 2nd batch of Altbier, brewed on 3/17/12, only had 66.29%. The only difference that I know of is the 1st batch was 5.5 gallons and the 2nd batch was 5 gallons, however I did adjust the grain bill to reflect this difference.
My Bourbon Barrel Porter, on the other hand - had amazing efficiency: 83.10%! Also I brewed an Octoberfest on 4/24/12 that had 82.65% efficiency. And a Cream Ale brewed on 4/30/12 had 77.80% efficiency. These were all 5 gallon batches. My grain crush is the same every time, I use the same brew process every time (I batch sparge, by the way).
As you can see - they vary widely. It's kinda difficult to formulate a recipe when I can't predict these inconsistencies. Is this normal? Does anyone have this issue?