Estimating Extract Efficiency When It Varies With Original Gravity

Scan 2015-2-10 0006-1As I outlined in the previous article, one reason for decreasing extract efficiency when brewing higher-gravity brews is that some brewers boil the same volume of wort, regardless of the size of their grain bill. If you do so and use continuous sparging, the volume of sparge water you use decreases as your grain bill gets larger. As such, the larger the grain bill, the fewer sugars are rinsed from the grain bed after the first wort had been run off. The same can be true if you batch sparge and your pre-boil volume does not go up with bigger grain beds.

Equivalently, with an unchanging boil volume in a “straight” BIAB system — one in which the bag is hoisted from the mash tun/kettle and allowed to drip, but isn’t sparged — larger grain bills mean higher gravity wort. When the grains are removed, the wort retained in the grain bed is the same gravity as the free wort. The volume of wort retained by the grain bed is also larger with larger grain bills. As such, progressively larger grain bills equate to more sugar being removed from the kettle by the bagged grains. More wort is retained by the grains and that wort is of higher gravity.

As I mentioned, in order to preserve your extract efficiency, you need to ensure that you completely sparge your grain bed. However, for some brewers, this is either not possible or inconvenient. The next best thing would be a way to predict your extract efficiency for whatever original gravity you desire — and there is one way easy way to do this. The catch is that you need to have had taken good notes for your prior beers.

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