What is the "Assumed" Pre-Boil Volume?

[dustinboyd]

I've searched around and couldn't quite find the answer to my question...

My system boils off about 2 Gallons per hour. When I find a recipie that gives a Pre-Boil Volume of 6.5 gallons, I adjust the grains to match my system and Pre-Boil Volume of 7.5 gal so I end up with 5.5 gal in the frementer. For example if the recipe called for 7lbs of 2-Row, I divide by 6.5 (original recipe Pre-Boil Volume) to get 1.08 lbs of 2-Row per gallon of Pre-Boil Volume, and then multiply by 7.5 (my Pre-Boil Volume) giving me a new total of 8.07lbs for my system. This let's me hit the OG on the dot once all finished. I don't mess with the hops volumes or schedules at all.

My question is, when a recipe doesn't list the Pre-Boil Volume, what is it assumed that the volume is? Is 6.5 gal the "standard"? I want to be able to properly adjust my grains so I get the correct OG, but I can't do that without knowing what the recipe was originally calculated for.

I appreciate the help, thank you!

 

[dkevinb]

There are a lot of different ways to look at this. I do BIAB. I prefer to think of the OG and the post-boil volume when formulating recipes. If I use x amount of grain and I wind up with y amount of wort I will have an OG of z, given that I have a pretty good idea of the kettle efficiency of my system. In other words, if I use 10 pounds of 2-row mashed in 7.5 gallons of water and boil down to 5.5 gallons of wort I will have the same OG as if I'd used 10 pounds of grain in 6.5 gallons of water and boiled down to 5.5 gallons of wort, given that my kettle efficiency doesn't change. If I start with a certain amount of sugar and wind up with a certain amount of wort it doesn't matter how much water I started with. The catch is keeping the efficiency the same.

Different boil volumes will have a slight impact on hop utilization, but not a tremendous amount for the differences we're talking about. You also don't want to oversparge to make up boil volume.

 

[pricelessbrewing]

I've searched around and couldn't quite find the answer to my question...

My system boils off about 2 Gallons per hour. When I find a recipie that gives a Pre-Boil Volume of 6.5 gallons, I adjust the grains to match my system and Pre-Boil Volume of 7.5 gal so I end up with 5.5 gal in the frementer. For example if the recipe called for 7lbs of 2-Row, I divide by 6.5 (original recipe Pre-Boil Volume) to get 1.08 lbs of 2-Row per gallon of Pre-Boil Volume, and then multiply by 7.5 (my Pre-Boil Volume) giving me a new total of 8.07lbs for my system. This let's me hit the OG on the dot once all finished. I don't mess with the hops volumes or schedules at all.

My question is, when a recipe doesn't list the Pre-Boil Volume, what is it assumed that the volume is? Is 6.5 gal the "standard"? I want to be able to properly adjust my grains so I get the correct OG, but I can't do that without knowing what the recipe was originally calculated for.

I appreciate the help, thank you!

The pre boil OG and pre boil volume usually are not listed in a recipe, the post boil are as that's what's going into the fermenter. Don't worry about your preboil volume being bigger than theirs...

Unless otherwise noted, assume that it's 1 gallon boil off s that's pretty common. However like I said above, you shouldn't need to adjust the grain bill off of this alone. If your mash efficiency and equipment losses are different THEN you need to adjust your grain bill to compensate.