Equipment Profile - water loss during boiling

I'm returning to brewing after a long (14 year) hiatus and will be brewing a dunkelweizen as my first batch this weekend. I'm using DME and specialty grains and spent some time this evening experimenting to find out what my water losses will be during a 1 hour boil. I really wanted to try a full-volume boil to hit a 2.5 gallon fermenter volume, but after I finished my little experiment, it looks like a full-volume boil will be a no-go for me until I get a larger pot.

Equipment: 20 qt stainless steel pot, electric ceramic-top range

I filled my pot w/ three gallons of water and turned the burner to it's highest setting. I was able to achieve a steady rolling boil in about 25 minutes. Once the boil started, I set the timer for an hour and let the boil run uncovered.

After the hour, I removed the pot from the stove and covered it, trying to simulate my cooling. Once cool, I measured the remaining amount and discovered I had lost almost exactly a gallon.

So, for me the moral of the story is that I would have to boil 3.5 gallons in a 4 gallon pot... and I don't think that is a great idea. With about an inch from the top of the pot I think the potential for a bad boil-over is too great so I will use a boil volume of three gallons and top off my fermenter to make up the difference.

Oh well, at least I know. Sort of a neat thing to do to get to know your equipment better without wasting any beer. I also know that I will not be able to generate a really solid rolling boil on my stove, but it should be good enough. I'm sure that if I used my propane burner I could boil harder and quicker, but that's not going to happen until I'm ready to go bigger and gp all-grain.

It's a learning process.

Cheers!

I just did my first batch...a full volume boil. While I do have a large 44 qt. pot, the beersmith program was off as far as volumes go. It won't/didn't figure in trub loss. For example...it told me to go with 5.7 gallons of water, and I also used a yeast starter adding another 32 oz(.25 gal).  While it appears I had the same evaporation you did(1 gal), I measured 10 cups(.625 gal) of trub after I racked to my secondary. And in my secondary, I already have a solid 1" of trub on the bottom of it....I am guessing 5 cups(.312 gal). So, I am looking at a bottling volume of around 4 gallons. :-\
My next batch, I plan on going with a boiling volume of 5.8 gallons. It may not be perfect...but will be pretty darn close!

That's interesting! Some of the calculators I've seen suggest a loss of up to 6 qts in a one-hour boil. It's also interesting that our loss rates are very similar - our boilers, although not the same size, must have similar ratios in terms of dimensions.

I do not know what other losses I may incur... we'll find out soon. I'm brewing my first batch this weekend!

I asked the owner of the local home brew shop about evap...he suggested 1 gallon as typical. What I didn't know was the amount of trub to expect. and to be honest...I kinda didn't think of it.