How do you do a full boil?
 

I started two weeks ago with a five gallon pot, got excited, and tried to boil four gallons to start, having read that the more you are able to boil the better the beer will be.

Result: the boiling water hopped out when the hops hopped in. Lost some; had to clean a stove. Everything else seems to have gone fine, bottling next week.

Fast forward to today: 36 QT pot, partial mash. I started with 7 gallons of water to allow for some to boil off, however, I ended up with a similar issue (boil-over, though I did end up with almost exactly 5 gallons). Luckily this one was outside on a Bayou burner, so there's no cleanup. But I don't like losing or loosing wort.

What is the best way to do this? Start with 5 gallons, and add water during the boil if the amount seems low? Twenty gallon pots?

Generally you'd want about 30% extra space. That way you will have enough room for expansion due to heating and then enough room for the hotbreak and foaming associated with boiling. It's either that or you could watch your boil a little more closely and turn the flame up as your liquid reduces.

Some also opt to use fermcap-s to help control the foam and reduce the risk of foam-over/boil-over.

Personally, I just make sure I have 2-3 gallons of headspace in my keggle before the boil starters. :D

I boil 7gals in a 36qt pot. Its a little scary at first but just go easy on the gas until its boiled off a bit more space. And get a spray bottle filled with water to fight the foam. The first 15minutes of boil require very close attention.

When do you add, say, DME during your boil? After the first 15 minutes? Every single boil-over I have had has been right after adding an ingredient.

Oh, now I notice people mentioning that you have to change the hops if you do a full boil; I didn't do that. We shall see what I get.

I usually add about a couple of pounds of DME into warm water, as I'm heating up for the boil, so as there's no steam making the DME clump on the bag then bring to a boil, add bittering hops etc. Etc. Add the majority of extract at around the last 10 minutes, or at flame out with Liquid HME Kit cans. You're right in that the boil definitely starts to get pretty lively directly after making a hop or DME addition.

Yes, you get better hop utilisation in full volume boils. I think that most recipe calculators figure your AA% yield based on a full volume boil so you're probably going to be alright with your batch. What was your hop schedule and recipe?

I found that turning the flame down to low while adding hops or dme helps, but won't necessarily eliminate the boil over

I used this as close as I could, but modified based on what was on hand:

http://beerrecipes.org/showrecipe.php?recipeid=102

so I had:

5 pounds, golden light DME
2 ounces, roast barley
8 ounces, crushed crystal malt
1 ounces, Fuggles (loose)
2 ounce, Goldings (loose)
1/4 ounce, Goldings (pellets)
1/2 ounce, Goldings (pellets)
WLP002

It was pretty close to that, but the hops were done 2 oz at 10 minutes after start of boil (after DME), and then 1 oz about 30 minutes before end, and then the rest at the end.

I have more details in my log, but it's not with me.

Get a plastic spray bottle something like you would use to spray clothes when ironing. As soon as your wort begins to boil spray water on it. That usually works for me,and of course I turn down the flame at the same time. Same thing when adding your hops. MAN THE SPRAY BOTTLE. I haven't had a boil over in a year. I'm doing smaller boils say 2.75 gallons in a 4 gallon pot. That's only 1.25 gallons of space to play with. You only have 2 gallons of play space if my math is good, but I think you can manage it fi you watch carefully.