First full boil, how much water should I use?

It depends on your boil time and your evaporation rate. I think the average evaporation rate is something like 10% per hour, but that can change depending on your setup (ex. brewing inside on an electric burner vs. outside with a propane burner). I'd start with 5.5 gallons for a 60 minute boil and then tweak from there.

 

Rather than guess, I would bring a known volume of water (say 6 gallons) to a boil for 15 minutes, let cool, and measure. (Original Volume - Final Volume) X 4 = Hourly Boiloff Rate

 

Volume per hour is a better parameter than % per hour. The former is (appropriately) constant across a range of possible batch sizes. The latter scales the boiloff volume (inappropriately).

 

8.75 gallons is the limit in my 10 gallon kettle. Beyond that, boil over prevention gets tricky. Find your kettle limit and roll with it.

6.5 total gallons is probably a good place to start for an 8 gallon kettle. Don't forget to include the volume of the ingredients. This implies using less than 6.5 gallons of water.

It also depends on how much you want to put in the fermenter and how much you are willing to leave in the kettle as trub. Some people dump the entire kettle in the fermenter. I prefer to leave trub in the kettle.

 

6 gallons for a 60 minute boil in an 8 gallon pot causes boil overs for me when i add dme anywhere from 5-8 lbs and it boils over even when adding half at a time. I need a bigger pot!!

 

I brew all-grain,
I have a 33qt pot (8.25 gallons) and I can get to just below 7 gallons without boiling over, unless it's a really big stout (For some reason those seem to foam up more than lighter beers for me.) between 6.5 and 7 nets me to 5.5 in the fermenter.
For extract, you probably want a bit more room, so maybe 6 gallons. As you mentioned, adding the extract in stages seems to help things - I got much better beer when I did extract by adding half at the beginning, and the other half with about 15 minutes left.

 

I do 5-gallon BIAB batches (by which I mean 5 gallons packaged, so 5.5 into fermenter) in my 10G pot and I've come close to boilovers a few times, especially when adding hops. With an 8 gallon kettle, you might want to stick to 4 gallon batches to be safe. At the very least, you'll have to stick to smaller beers with shorter boil times - the dubbel I made recently with a 90 minute boil came really close to overflowing.

Let us know when you try BIAB! I think it's a great way to make beer, personally.

 

I have an 11 gallon pot for ~5 gallon batches and I'm still dialing in the boil off rate. I've been adding 6.5 gallons, but I think next time I'll go with 6, especially with the cooling weather and my volumes being a bit higher (and in turn lower OG) than I'd like. And unless you have a massive pot I think boilovers are always a concern. I keep a close watch on mine and have had to lower the flame a few times to avoid a mess.

 

when I moved up to my keggle, 15.5 gallons, I assumed boil overs were a thing of the past. not so. less common, but the sound of a flame being extinguished with liquid does still happen if I'm not paying attention.

an 8 gallon pot is fine for 5 gallon brews. 6.5 gallons is about the volume limit though.

also, remember that larger volumes get heavy, so plan ahead. you don't want to have to move 7 gallons of boiling wort.
Cheers.

 

A few folks have discussed boil over issues.

There is a product which could be helpful here: Fermcap S

“An anti-foam agent that can be used during fermentation to eliminate messy blowoff. Can also be added during the boil to reduce the risk of boilovers.”

I have used Fermcap S a few times to mitigate krausen during the fermentation of high gravity beers. It has been very helpful for those situations.

Maybe some of you would like to try this to manage boil overs in your kettle.

Cheers!

http://www.northernbrewer.com/shop/fermcap-s-1-oz

 

Fermcap is my baby. I use it in starters and my boil. I feel it has a shelf life, my last brew almost boiled over as if I hadn't used it at all.
Also, @VikeMan has the best advice. Figure out what your boil off is for your set up. My kettle is larger in diameter and circumference (obviously) than most kettles and I am at altitude. My boiloff is over 1.5 gallons an hour, my stout was almost 2 gallons as the boil was aggressive.

 

I have never had problems with head retention while using fermcap.

 

I have also had no problems with head retention using Fermcap.

Cheers!

 

Fermcap is supposed to improve head retention in fact. some of the head forming compounds that would be blown off during fermentation are retained if you use it in the fermenter.

Fermcap is like crack for brewers. it's real good shit man. real good. you use way more than you are supposed to and don't even care. then you get more and more of it so it is always available. the only cure for my Fermcap addiction was a 15.5 gallon kettle. just get a little fermcap. it's cheap, you'll like it. trust me.

Cheers.

 

If you are concerned about a boil over don't add all of the extract at the beginning of the boil. A lot of people do this anyway for other reasons. Save half or more and add it with 15-20 minutes left. Just make sure to cut the heat before doing so.

 

Combining the logic in these two posts... you can just use like 2 gallons instead of 6 for your test boil. That's significantly quicker and should still give you the relevant information.

 

Yeah...that would get you close. But the closer to a realistic batch volume you get, the more accurate the test. Only because very small volumes can (with the same heat) boil more vigorously, and thus skew the boil-off measurement a little.

 

Definitely do a test batch with some water. I'm finally used to my system, but realized that my 10 gal kettle is super thin, which makes my boil off rate pretty high. If I'm brewing a 5.5 gal batch for example, and a 90 minute boil I'll need at least 8 gal pre-boil wort. All systems are different though, so adjust yours as necessary but vikeman brings up a good point.