Question about losing water when boiling

[earwig]

So far every time I boil my wort I start out with 2.5 gallons, cool it, throw it in the fermenter and add another 2.5 gallons. Each time I end up with about 4.5 gallons... should I just add 3 gallons to it instead of 2.5 to bring it to the 5 gallon mark? Do you guys just drop your hydrometer in there and add water watching the hydrometer to make sure it stays where you want it? I'm afraid of adding too much water to the boiled wort, but I'm also afraid of starting with too much water in the boil pot because I don't want to mess up the hop acid balance of the recipe. Thanks!

 

[mojotele]

Just add 3 gallons instead unless you're happy with the original gravity at 4.5 gallons.

I never put my hydrometer in the fermenter. I always draw off a sample and measure it in the tube for my floating thermometer - mostly because it is easier to read that way.

 

[FreeM80s]

I started boiling extra water just in case I have more boiloff than I expected or if I am using a lot of DME. 1-2 gallons usually...

 

[Frank99]

Something doesn't seem right. If you "start off" with 2.5 gallons and try to cool this slowly you can easily burn off 1/2 gallon in evaporation, which is probably where the 1/2 gallon is going. I would recommend doing a full boil or as close to a full boil as your brewpot will allow. I'm not sure I understand the "hop acid balance" issue you're having. Start off w/6-7 gallons in the brewpot if possible and boil with the lid off. After an hour you'll have your 5 gallons.

 

[mojotele]

I'm not sure I understand the "hop acid balance" issue you're having.

The lower the gravity of the boil the more IBUs you get out of the hops.

 

[JiveTurkey]

Whatever you end up at post-boil, top off to whatever your recipe calls for in the fermenter (e.g. 5 gallons).

If this is for extract (with or without specialty/steeping grains), assume whatever Beersmith or another program predicts for the OG; don't trust your hydrometer. As long as the batch size and ingredients are correct, you can't really miss the OG. However, if you measure it yourself, you might think you're off because it is very difficult to completely mix the boiled wort and top-off water. So, putting the hydrometer in and adding water till you get the SG you want won't work.

When it comes to gravity, it doesn't matter how big or small your boil size was, as long as you top off with whatever you need to post-boil to end up with the correct batch size (e.g. 5 gallons).

However, as mentioned above, the density of the boil does affect hop utilization. An easy fix is that if you're doing a partial boil, only boil part of your extract and add the rest immediately after the boil (and let sit for 5-10 minutes to pasteurize).

An even easier thing is to use Beersmith or a similar program and input your batch size, boil size, extract to be boiled, extract post-boil, specialty grains, and hops; and see what your IBUs end up at. IBUs can be changed by varying the boil density (amount of extract/grains added pre-boil and boil size) and/or amount of hops (along with their type, boil time, etc.).