Author Topic: Wort vs water boil off rate?  (Read 3674 times)

Offline trapae

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Wort vs water boil off rate?
« on: February 10, 2019, 09:11:03 pm »
 Does anyone know if there is, and what is the difference in boil off rate between wort and water?  I just got my new SSbrewtech electric kettle and did a test brew day with water just to get the volumes down in the new kettles and time to strike and time to boil.   I got about 1.2 gallons boil off rate per hour.   Just wondering if that is going to be pretty close to a wort boil off rate?
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Offline KellerBrauer

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Re: Wort vs water boil off rate?
« Reply #1 on: February 11, 2019, 06:16:27 am »
That sounds about right.  The boil-off rate should be the same for wort as it is for water being the compound that’s getting boiled off is the same — water.  My boil off rate is 1.5 gallons per hour.  However, my kettle is 18” in diameter.  The more exposed water/wort surface area, the greater the boil-off given the same BTU input.
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Big Monk

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Re: Wort vs water boil off rate?
« Reply #2 on: February 11, 2019, 06:19:50 am »
Does anyone know if there is, and what is the difference in boil off rate between wort and water?  I just got my new SSbrewtech electric kettle and did a test brew day with water just to get the volumes down in the new kettles and time to strike and time to boil.   I got about 1.2 gallons boil off rate per hour.   Just wondering if that is going to be pretty close to a wort boil off rate?

It should be pretty close.

That sounds about right.  The boil-off rate should be the same for wort as it is for water being the compound that’s getting boiled off is the same — water.  My boil off rate is 1.5 gallons per hour.  However, my kettle is 18” in diameter.  The more exposed water/wort surface area, the greater the boil-off given the same BTU input.

Per KellerBrauer’s comment, what was your boil intensity like? Keep in mind that you can always lower the heat input and this the intensity if you want to manipulate the boil off amount.

Offline BrewBama

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Re: Wort vs water boil off rate?
« Reply #3 on: February 11, 2019, 06:44:00 am »
What size batch into the fermenter and what starting volume are we discussing?  In a 10 + gallon batch 1.2-1.5 gal/hr boil off is most likely very good. If it’s a 5 gallon batch you might consider reducing it. 


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Big Monk

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Re: Wort vs water boil off rate?
« Reply #4 on: February 11, 2019, 06:55:19 am »
What size batch into the fermenter and what starting volume are we discussing?  In a 10 + gallon batch 1.2-1.5 gal/hr boil off is most likely very good. If it’s a 5 gallon batch you might consider reducing it. 


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^^^^
THIS.

Depending on the pre-boil volume, 1.2 gallons of boil off in a 5 gallon batch would be close to 20%.

Offline trapae

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Re: Wort vs water boil off rate?
« Reply #5 on: February 11, 2019, 07:20:00 am »
 Pre-boil volume before changing kettles was 8.5 gallons,  with 1.5 gallons per hour boil off on the old system.   I could definitely reduce the boil vigor now that it is an electric system and I can just decrease the percent output. And I’m sure the low oxygen guys would tell me to do this anyway. The math would sure be easier if it was just 1 gallon per hour.
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Big Monk

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Re: Wort vs water boil off rate?
« Reply #6 on: February 11, 2019, 07:39:21 am »
Pre-boil volume before changing kettles was 8.5 gallons,  with 1.5 gallons per hour boil off on the old system.   I could definitely reduce the boil vigor now that it is an electric system and I can just decrease the percent output. And I’m sure the low oxygen guys would tell me to do this anyway. The math would sure be easier if it was just 1 gallon per hour.

That’s about 18% boil off.

For sure there is the topic of boil stress but also side topics like increased mineralization (if you aren’t subtracting our boil off in your water calcs you can have much higher mineral content in the final beer), etc.

If you can reduce boil vigor and total boil off, I’d say it’s for the better.

Offline mabrungard

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Re: Wort vs water boil off rate?
« Reply #7 on: February 11, 2019, 06:29:34 pm »
Unless you're brewing with a large percentage of pils malt, you don't need to boil off high percentages of your wort. Limiting the evaporation loss to around 8 to 10 percent is more than sufficient to make great beer without any DMS.
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Offline Robert

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Re: Wort vs water boil off rate?
« Reply #8 on: February 11, 2019, 06:45:33 pm »
Unless you're brewing with a large percentage of pils malt, you don't need to boil off high percentages of your wort. Limiting the evaporation loss to around 8 to 10 percent is more than sufficient to make great beer without any DMS.
Martin, I thought 8-10% was adequate even for Pilsner malt, as long as you have good circulation?  Seems to be my experience,  and IME Pilsner malt flavor seems to suffer badly with excess heating (no different than any other malt though.)  Is there ever a case where it is categorically necessary to  boil off more than 10%?  (Still wish Portland had had competent audio techs, can't wait for a Zymurgy article!)
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The Beerery

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Re: Wort vs water boil off rate?
« Reply #9 on: February 11, 2019, 06:56:54 pm »
Hell I am at around 4% now and All my grain bills use pils malt. 


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Offline BrewBama

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Wort vs water boil off rate?
« Reply #10 on: February 11, 2019, 08:03:52 pm »
This all brings up an interesting point: how to properly calculate boil off percent.

The More Beer calculator is what I’ve been using which gives a 14.22% rate for 8.5 gal pre boil with a boil off of 1.5 gal.  https://www.morebeer.com/content/boil_off_rate_calculator

I think I am not using the same calculation as others because I struggle to hit 8% (by the More Beer calculator). It sometimes creeps higher.


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Big Monk

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Re: Wort vs water boil off rate?
« Reply #11 on: February 11, 2019, 08:13:13 pm »
This all brings up an interesting point: how to properly calculate boil off percent.

The More Beer calculator is what I’ve been using which gives a 14.22% rate for 8.5 gal pre boil with a boil off of 1.5 gal.  https://www.morebeer.com/content/boil_off_rate_calculator

I think I am not using the same calculation as others because I struggle to hit 8% (by the More Beer calculator). It sometimes creeps higher.


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What’s your heat source?

Offline BrewBama

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Wort vs water boil off rate?
« Reply #12 on: February 11, 2019, 08:25:53 pm »
Induction.  I struggle to get a good roll at 2000w but get a bit too much vigor at 2400w. I’d love a setting for 2200w but it is preset. I have the BK wrapped with insulation and may remove a layer.

...but what does my heat source have to do with the proper calculation to use for percent boil off?  (Jk)

(Edited to correct wattages. I was off by 400w)
« Last Edit: February 12, 2019, 10:35:26 am by BrewBama »

Big Monk

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Re: Wort vs water boil off rate?
« Reply #13 on: February 11, 2019, 08:47:39 pm »
Induction.  I struggle to get a good roll at 2400w but get a bit too much vigor at 2800w. I’d love a setting for 2600w but it is preset. I have the BK wrapped with insulation and may remove a layer.

...but what does my heat source have to do with the proper calculation to use for percent boil off?  (Jk)

 :)

Nothin really I guess.

Just trying to help you get that percentage down. Reducing the source heat input is the easiest way.

Offline Robert

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Re: Wort vs water boil off rate?
« Reply #14 on: February 11, 2019, 09:16:50 pm »
^^^^
Actually, heat source does have somethin' to do with it maybe.   Induction is heating very evenly, so you won't get circulation until there's a strong upwelling all over, and the walls of the vessel force some of the wort to go somewhere (i.e., to the center and back down.  Or the other way I suppose.)  OTOH,  I use direct flame.  I heat my kettle asymmetrically.  (It sits over two burners on my stove, so it's easy to set them differently.)  This naturally causes the wort to rise vigorously on one side and descend on the other.  I get a good roll at a fairly minimal application of flame.   [Commercial kettles that heat too evenly to induce circulation at minimal heat incorporate mechanical agitation.]  I wonder if you could find a way to mimic what I do, inducing a more vigorous boil on one side.  I don't fully understand the operation of induction cookers (the range over which the field is effective,) but -- could you place some random stainless hardware on the bottom of your kettle on one side?  Would that generate more heat there?  Just thinking.
« Last Edit: February 11, 2019, 09:43:05 pm by Robert »
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