I've heard that higher gravity beers will see a lower efficiency, but my understanding for the cause is a reduced amount of sparge water with a standard all grain brewing process. Since BIAB doesn't require a sparge, would this phenomenon still exist? The reason I ask, I did my third all grain BIAB yesterday, a planned 1.077 beer, and only got 64% versus my first two of 70%. Another potential factor: Could water to grain ratio also be a cause? My first was 2.5 qt/lb, 70%, 1.054, second was 3.8 qt/lb, 70%, 1.043, and third 1.5 qt/lb, 64%, 1.067, planned of 1.077. The reason my water to grain ratios differ is because of a small boil kettle limitation. I have been leaving out some water during the mash and adding it for the boil after grains are removed.