how much boil off?

[mw20]

How much boil off are you guys getting on a 60 minute full boil. I just kegged a amber ale last night that came up about a half gallon shy. I marked all my carboys today so I could be sure that I'm getting the right volume in the carboy from now on. This batch was at 7 gallons pre-boil. Does 2 gallons of boil off sound like a lot for a 60 minute boil?

 

[flyangler18]

No, that sounds about right. I start with 8 gallons pre-boil, 6 at the end of the boil, 5.5 into the fermenter, 5 into the package.

 

[mw20]

Thanks Flyangler, I just didn't know if I was boiling too vigorously. I'm gonna do my first 10 gallon batch this weekend and want it to come out as close as possible to my five gallon recipe.

 

[flyangler18]

I really should revise my earlier statement with a 'well, it depends.'

I tend to boil-off less in the winter than in the summer, all things equal. If the wind is going strong, I'll wind up boiling away a little less.

Ultimately, it comes down to knowing your system and calibrating accordingly. For example, I usually wind up boiling at least 75 minutes total time, adding my bittering hops at 60 minutes after the hot break passes.

 

[nyer]

I really should revise my earlier statement with a 'well, it depends.'

I tend to boil-off less in the winter than in the summer, all things equal. If the wind is going strong, I'll wind up boiling away a little less.

Ultimately, it comes down to knowing your system and calibrating accordingly. For example, I usually wind up boiling at least 75 minutes total time, adding my bittering hops at 60 minutes after the hot break passes.

I'm getting the opposite. During warmer weather I boil off about 1 gallon per hour. The other day I did two batches in my garage that was between 25-30 degrees. I lost almost 2 gallons on a 1 hour boil and almost 2 1/2 on a 1.5 hour boil.

 

[Laughing_Gnome_Invisible]

I found I have more boil off in colder weather too. I am now officially confused.

 

[Edcculus]

What it boils down to....

ok all puns aside. I dont have beersmith in front of me, and I don't remember the forumula for boil off. If you calculate your % boil off, it should be between 10-15%. Depending on your system, somewhere around 12% is optimal. If you are getting a large % boil off, consider turning the gas down. You want a vigorous boil, but the wort doesn't need to be flying out of the kettle.

 

[maltMonkey]

I get about 2 gallons/hour boiloff too, which is pretty consistent, but there have been times where I was left scratching my head when I got way under or over that.

Here are some things I've noticed affect my evaporation rate:

-- The more humidity in the air, the less boil off you will have (generally). So even though it is colder in the winter, it is usually less humid which causes a higher evaporation rate.
-- Assuming you are using propane burners: sometimes when the propane tank gets near empty, I've noticed that they don't send the gas out with as much pressure, which causes a lower heat on the kettle.
-- If the wind is blowing strongly through the burner it can "deflect" the fire, causing lower heat to the boil kettle.

Some things to consider when calculating your volumes before/during the boil (these have screwed up my evaporation calculations before):

-- The temperature you measure your initial boil kettle volume matters. If you start heating the boil kettle during the sparge so that it's near boiling by the time the sparge is done, you will be overestimating your actual volume since a liquid at 212°F will take up more space than one at room temperature. I can't remember the exact number, but I think that a boiling liquid will have 4% more volume than at room temp, so if you collect 7 gallons of room temperature wort, it will take up about 7.25 gallons when at a boil
-- Wort chillers take up space in the kettle. So do hops, if you use a lot of them.

 

[AnOldUR]

I think that the biggest factor is surface area of your wort. A tall skinny pot will boil off less than a short wide one. That being said, the percentage that BeerSmith uses is misleading. If you boil off 2 gallons in an hour while doing a 5 gallon batch, you will boil off almost the same 2 gallons with the 10 gallon batch that you are planning if you use the same pot.

 

[remilard]

Yeah the thermal expansion of water from 25 C to 100 C is about 4%. Just like boiling temperature, wort might as well be water when it comes to thermal expansion.

 

[maltMonkey]

...That being said, the percentage that BeerSmith uses is misleading. If you boil off 2 gallons in an hour while doing a 5 gallon batch, you will boil off almost the same 2 gallons with the 10 gallon batch that you are planning if you use the same pot.

Agreed, you should never go by percentages for boil off rate. All you need to know is how many gallons you lose per hour, and be able to consistently match that.

I use Beersmith and love it, but I use a program I wrote myself to calculate boil-off and pre-boil volumes, because it is a giant pain to keep playing with the evaporation % in beersmith until you get your gallons/hour correct.