Help lowering boil-off rates

So, we moved into a house in June, and with the added space, I decided it was a decent opportunity to move to all-grain brewing. Leaving myself a little room to grow, I bought a 15.5-gallon kettle and an SP-10 Bayou Classic propane burner.

I've done 3 all-grain batches. The first, I didn't use enough sparge water, so when I ended up short of my 5-gallon target, I redid the math and realized my mistake. The second batch, I did a simple cream ale for SWMBO and collected just shy of 6.5 gallons. Post-boil I just a hair over 4 gallons in the fermenter (I topped up with bottled water). I decided I had way too vigorous of a boil going on, so I attempted to correct that this past weekend. I collected 6.25g of wort, and after a 60-minute, barely-rolling boil (less vigorous than I used to do on my stovetop with extract when I didn't care about boiloff) I put about 4.6 gallons in the fermenter. That's around 25%.

The first two batches, I made obvious mistakes, but this last batch surprised me. They've all been fairly simple, 5-gallon (target) ales, so I don't know what I can try to get lower rates. Granted I'm brewing in the garage now and it was probably 45F in there this weekend, but no breeze, and it was close to 60F with the cream ale.

FWIW, my pot diameter is 16". I see the 15-gal Megapot is 19". Appreciate any advice.

 

Well, first, you do want a good vigourous boil, not a wimpy little bit of bubbling, but I'm sure you know that. Boil off rate, among other factos, is a function of surface area presented to atmosphere. Your kettlle has a large surface area. A kettle of less diameter would put you back into more familiar grounds...

 

kick it up to about 6.7 gallons of wort. that should get you 5 post-boil

 

faster boiloff is a blessing. as long as you boil takes 60 minutes, you should be able to fit in all you hops additions. unless you constantly have a several inches of foam, i don't think you're burning too hot.

water expands when it's hot. 7 boiling gallons might shrink down to 6.5 room temp gallons.

what is the elevation of where you live/brew?

 

I used to have around a 25% boil off until I switched to a better burner. Now its right at 12%.

 

Which burner did you switch to?

I did my last batch with a 15 gallon pot and SP-10 and boiled off way more than you did. With the old pot 1.5-2 was usual, with this thing I went from 8 to a little less than 5.5 including with the trub going in.

 

I'll try that with the next batch. I'm wanting to do a 10-gallon batch that I can split with a buddy. Does something like this scale more or less linearly? Meaning if I want 10-gallons post boil we'd need to end up with nearly 13 gallons of runnings?

 

I have a keggle and have to create my recipes to start with about 7.25 gallons preboil to end up with 5.5 gallons post boil at the desired gravity.
do you have brewing software or are you manually calculating it?

 

I boil off a gallon per half hour. There is nothing wrong with the high boil off. I usually do six gallon batches so that I can get 5 into the fermenter after trub. For a six gallon batch I start at just over 8 gallons pre-boil.

Rather than boiling slow or worrying about reducing the amount of boil off I would just focus on upping your pre-boil volume based on what you boiled off this first batch. After another couple batches you will have it nailed down and will be able to hit your target volumes spot on.

 

I use a Blichman burner now. It heats the entire bottom of the pot even when turned down real low so you get a nice even heat transfer. It`s a great burner.

 

+1

Brewing software has really made a mess of this.

In the software you enter a % to determine boiloff, but that's not how it works. Like Yooper and Sudbuster said, it is a fixed amount. The amount will change based on a bunch of variables like temp, humidity, wind, etc... but you will not boil off twice as much going from 5 to 10 gallons if you do it in the same conditions.

Once you figure out the amount, just account for that in future brews.

Ed

 

I'm using beersmith. I'll up the boiloff rate to what I've been seeing over these last couple batches and see how I come out on the next batch. I wasn't sure if I was doing something wrong of it boiloff just is what it is for a given setup. I guess this higher rate isn't as uncommon as I thought it was.

Yeah, that makes sense, Yooper. I obviously wasn't thinking when I left that earlier. That'll learn me to comment pre-coffee

 

I agree with some of the above posters, just pay attention to your gravity readings and sparge with extra water in the future.

 

Boil off is also dependant on Relative Humidity. I find it helps to have a cheap hygrometer in the brewhouse to help guage what to expect. Over the years I have learned that in teh dry winter months my boil off volume is .5x times greater than in the wetter summer months and I adjust accordingly.

 

My concern with it is more along the lines of "Hey, I can use 1/3 the amount of gas with this new burner and still maintain a proper boil".

 

I can attest to the surface area of the kettle affecting boil off rates... My kettle has a wide surface area and I need 8 gals preboil to end up with 5.5 in the fermenter no matter how softly I try to boil...Just up your grain bill and preboil volume and roll with it.I really thought I was doing something wrong for the longest time, but it was just normal for my setup.

 

How much of an effect would it have on the final product if you were to add water during the boil? Obviously water close to boiling would be optimal.