Author Topic: Wort vs water boil off rate?  (Read 3673 times)

Offline KellerBrauer

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Re: Wort vs water boil off rate?
« Reply #15 on: February 12, 2019, 06:32:56 am »
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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This may sound too simple, but I simply measured my wort before and after boiling for an hour, then added that number into BS3.  Again, boil-off rate is determined by the BTU input and the exposed surface area of the liquid.  So, if Brewer A has a kettle that’s 20” in diameter and Brewer B has a kettle that’s 10” in diameter and both were applying 70,000 BTU’s of heat on the same burner, Brewer A would boil-off faster than Brewer B.
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Offline BrewBama

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Wort vs water boil off rate?
« Reply #16 on: February 12, 2019, 07:56:44 am »
The MoreBeer calculator takes shrinkage and time into consideration as well.  When one person says X and another says X they could mean two different X(s) based on how X is calculated.

My point was not that I get 8% boiloff rate (using MoreBeer calculator), my point is that I believe we’re not using a common language.

FWIW: The induction cooktop does produce and asymmetric boil pattern in my BK. 


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« Last Edit: February 12, 2019, 08:01:27 am by BrewBama »

Big Monk

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Re: Wort vs water boil off rate?
« Reply #17 on: February 12, 2019, 08:07:55 am »
The MoreBeer calculator takes shrinkage and time into consideration as well.  When one person says X and another says X they could mean two different X(s) based on how X is calculated.

My point was not that I get 8% boiloff rate (using MoreBeer calculator), my point is that I believe we’re not using a common language.

FWIW: The induction cooktop does produce and asymmetric boil pattern in my BK. 


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When I grab a new kettle of some sort, I do a boil test with water. I don't take shrinkage into account. I measure an amount of room temp water, boil for an hour, and then measure the remainder at room temp.

That's the value I input into my sheet. I only use modifiers for volume due to temperature in a standalone calculator within my sheet for tracking.

Offline Robert

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Re: Wort vs water boil off rate?
« Reply #18 on: February 12, 2019, 08:17:37 am »
For a given batch, how good is concentration as an indicator?   I know reduction in volume is not directly proportional to increase in gravity because some extract is lost in precipitation of break material, but has anybody figured out if it's "close enough?"  Or could it serve as a useful alternative indicator of thermal stress on its own, ignoring actual change in volume?
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Offline denny

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Re: Wort vs water boil off rate?
« Reply #19 on: February 12, 2019, 08:34:55 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?
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Offline BrewBama

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Wort vs water boil off rate?
« Reply #20 on: February 12, 2019, 08:57:26 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?

I dunno. Some brewer said 8-10% is the target boil off rate so being a good soldier I aim for the bullseye.

...and being lazy, I found an online calculator.

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« Last Edit: February 12, 2019, 09:03:33 am by BrewBama »

Offline denny

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Re: Wort vs water boil off rate?
« Reply #21 on: February 12, 2019, 09:42:30 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?

I dunno. Some brewer said 8-10% is the target boil off rate so being a good soldier I aim for the bullseye.

...and being lazy, I found an online calculator.

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I measure mine in gal./hour so it stays constant with batch size.
Life begins at 60.....1.060, that is!

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Big Monk

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Re: Wort vs water boil off rate?
« Reply #22 on: February 12, 2019, 09:43:00 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?

I don't actually use % based evaporation for calculations. It's just a reference value that I calculate.

For actual calculations, I use my 60 min. boil-off amount that was measured.

Offline denny

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Re: Wort vs water boil off rate?
« Reply #23 on: February 12, 2019, 10:08:37 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?

I don't actually use % based evaporation for calculations. It's just a reference value that I calculate.

For actual calculations, I use my 60 min. boil-off amount that was measured.

I was hoping that someone would make that distinction.
Life begins at 60.....1.060, that is!

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Big Monk

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Re: Wort vs water boil off rate?
« Reply #24 on: February 12, 2019, 10:11:38 am »
Why are you guys using percent?  Do you get more boiloff as batch size increases?

I don't actually use % based evaporation for calculations. It's just a reference value that I calculate.

For actual calculations, I use my 60 min. boil-off amount that was measured.

I was hoping that someone would make that distinction.

It's a landmark.

For calculations I use just my 60 minute boil-off value. Since i don't have any batches where I boil for longer than 60 minutes, I forego a time modifier.

It's also a "fat-finger" fail-safe in my spreadsheet. If i suddenly saw 50% boil-off, it would let me know I entered it wrong.
« Last Edit: February 12, 2019, 10:14:58 am by Big Monk »

Offline mainebrewer

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Re: Wort vs water boil off rate?
« Reply #25 on: February 12, 2019, 10:20:21 am »
For a given batch, how good is concentration as an indicator?   I know reduction in volume is not directly proportional to increase in gravity because some extract is lost in precipitation of break material, but has anybody figured out if it's "close enough?"  Or could it serve as a useful alternative indicator of thermal stress on its own, ignoring actual change in volume?
This is what I do. Comparing pre- and post-boil sg's works best for me. Since I use an immersion chiller, measuring pre- and post-boil volumes would be difficult, at best, for me. My process may not be accurate but it's a consistent benchmark for me.
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Offline BrewBama

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Re: Wort vs water boil off rate?
« Reply #26 on: February 12, 2019, 10:43:21 am »
https://youtu.be/xlKVC_Xij4k


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Big Monk

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Re: Wort vs water boil off rate?
« Reply #27 on: February 12, 2019, 10:47:56 am »
https://youtu.be/xlKVC_Xij4k


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What setting is that? 2.4 kW or 2.8 kW?

Offline BrewBama

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Re: Wort vs water boil off rate?
« Reply #28 on: February 12, 2019, 10:51:42 am »
2000w. I had to correct my previous settings above. I was 400w off.


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Big Monk

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Re: Wort vs water boil off rate?
« Reply #29 on: February 12, 2019, 10:52:49 am »
2000w. I had to correct my previous settings above. I was 400w off.


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And that yields too much or too little boil off?