Evaporation Loss

I'm sure this has been brought up, but is there a good way to figure out the amount of water lost in the boil? I begin with 10 gallons and I'm not sure what I end up with. Do you guys adjust for the loss and begin with more with the expectation of losing some in the boil? I guess I need a chart or something...Thanks, this forum is awesome!!

Evaporation is dependent on the surface area (vessel size), vigorosity of the boil, atmospheric conditions, etc.

I lose close to a gallon per hour. I use a keggle, I have a Banjo Kick-A burner which burns like a nitro funny-car and I live in the desert.

You must measure the final volume and determine what percentage that was lost from the initial volume. For example, I boil 10gal of wort for an hour and get a final volume of 9gal, this means my system has a 10% evaporation over one hour. Now that I know what to expect I can target volumes. For example, if I want to brew a 5gal batch, so I would boil 5.5 gal of initial wort, this should ensure that I have 5gal of wort in the fermenter.

Glad someone brought this up...I swear I'm loosing upwards of 2 gallons during a 60min boil. Is that typical? Normal? Whatever? Seems like an awful lot to me.

I live in San Diego so my altitude is like 10 feet. I brew in a keggle as well, so I guess I should just measure before and after and compare. I thought I was losing about a gallon to gallon and half in the boil, so that sounds like what other people are losing too. Thanks for the info...

Kilted Brewer said:

Glad someone brought this up...I swear I'm loosing upwards of 2 gallons during a 60min boil. Is that typical? Normal? Whatever? Seems like an awful lot to me.

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I don't know if it is typical but I loose 1.5 - 1.75 during my 70 minute boil. My kettle is quite wide though so that must be the major factor.

Kilted Brewer said:

Glad someone brought this up...I swear I'm loosing upwards of 2 gallons during a 60min boil. Is that typical? Normal? Whatever? Seems like an awful lot to me.

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Did my first full boil a few weeks ago and lost 1.75g. Thought I was going nuts, but glad to see I am not...

SilkkyBrew said:

Did my first full boil a few weeks ago and lost 1.75g. Thought I was going nuts, but glad to see I am not...

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I am losing about 1.5 gal / hour. My 17 gallon brew pot is alot wider than a keggel.

Iordz said:

You must measure the final volume and determine what percentage that was lost from the initial volume. For example, I boil 10gal of wort for an hour and get a final volume of 9gal, this means my system has a 10% evaporation over one hour. Now that I know what to expect I can target volumes. For example, if I want to brew a 5gal batch, so I would boil 5.5 gal of initial wort, this should ensure that I have 5gal of wort in the fermenter.

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Your evap rate doesn't depend on the amount you're boiling (at least not in the linear way you describe it here).

If you lose 1 gallon on a 10-gallon, 1-hour boil, you'll lose pretty close to 1 gallon on a 5.5-gallon, 1-hour boil under the same conditions.

You want to target a loss of about 8-15%. Less means your boil is not vigorous enough to drive off DMS and other unwanted compounds and more than 15% means you could be scorching your wort and create harsh and burnt tasting compounds.

To measure I record the pre boil volume. Then I check how much I have in the kettle after chilling. Make sure you account for the ~4% shrinkage that you get from chilling the wort. I generally start out with 25L (hot; equals about 24 L cold) and end up with 21L cold. For a 60 min boil this is about (24L - 21L) / 24L * 100% = 12.5%.

It's difficult for me to get a post boil pre chill reading since I have the wort chiller in the pot. I don't know its affect on the volume, yet.

Kai

Bike N Brew said:

Your evap rate doesn't depend on the amount you're boiling (at least not in the linear way you describe it here).

If you lose 1 gallon on a 10-gallon, 1-hour boil, you'll lose pretty close to 1 gallon on a 5.5-gallon, 1-hour boil under the same conditions.

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That's a good point. It basically depends on the amount of enery that you can get into the wort during the boil as well as the ambient pressure. But the affect of the pressure is much less than you think. Humidity shouldn't play a role either, though I'm not 100% sure about this.

Kai