Ask Mr. Wizard

Accounting for evaporation loss during an aggressive boil?


Rob Allen • Salt Lake City, Utah asks,

I just brewed an all-grain amber recipe from the May 1999 issue. This was my third all-grain attempt, and it raises a few questions. Since I started using a 100,000-BTU burner, I end up with a smaller volume than the recipes anticipate. I know this is due to a more aggressive boil, but I am concerned with having to top off my fermenter. Is this a problem? Should I start with more wort? Also, the recipe calls for the gravity to start at 1.064. My yield prior to the boil was 1.042. Does it change during the boil? Should I check it again after topping off to 5 gallons?


Recipes printed in BYO give the “original gravity” of the wort. This number refers to the specific gravity of the wort prior to fermentation-in other words, after the boil. Wort gravity increases
Response by Ashton Lewis.