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General Category => General Homebrew Discussion => Topic started by: SiameseMoose on September 21, 2011, 10:01:50 PM

Title: Is your boil-off volume reproducible?
Post by: SiameseMoose on September 21, 2011, 10:01:50 PM
I'm having a hard time predicting my boil-off volume. Two consecutive brews with the same boil time, and the first boiled off 2.5 gallons, but today was only 1.5 gallons. As far as I can tell, the only major difference between the two sessions was the humidity. Today I brewed in an on-and-off drizzle, so saturated humidity. The previous session was about 60% humidity. Today I even turned up the burner intensity because I saw that the boil off rate was low. I have to find a way to get a more repeatable figure. Any hints?
Title: Re: Is your boil-off volume reproducible?
Post by: Slowbrew on September 21, 2011, 10:06:05 PM
Ambient humidity does make a difference in your boil off.  I adjust my boil time to account for the anticipated differences.  On very humid days I add 20 - 30 minutes to the boil prior to my first hop addition.

Other than doing the boil in a controlled environment I haven't found a better way to manage it.

Paul
Title: Re: Is your boil-off volume reproducible?
Post by: tubercle on September 21, 2011, 10:40:51 PM
I use my stirring paddle with notches calibrated to nearest 1/4 gallon for my boil kettle. I stop when I get it to where I want it. Temp and humidity are no longer factors.
Title: Re: Is your boil-off volume reproducible?
Post by: a10t2 on September 21, 2011, 11:42:42 PM
Humidity will definitely affect the boiloff rate, but I don't think it could explain a 50% variation. I brewed my first fifty-odd batches in the Midwest, so there must have been some major changes in humidity, and I never saw anything close to that kind of discrepancy.
Title: Re: Is your boil-off volume reproducible?
Post by: euge on September 22, 2011, 02:28:22 AM
Yes it does make a difference but not that bad. Mine is predictable.
Title: Re: Is your boil-off volume reproducible?
Post by: Kit B on September 22, 2011, 02:24:47 PM
Several factors contribute, including:
Starting gravity
Humidity
Intensity of boil
Surface area of boiling liquid
Wind
Title: Re: Is your boil-off volume reproducible?
Post by: dmtaylor on September 22, 2011, 02:37:14 PM
I'm sure humidity does matter, although I'm not exactly sure how much it matters.  Probably just a little.  But you also mentioned that it was drizzling rain -- did the boil kettle get hit with drizzle during the boil?  This could also have cooled it down, preventing normal boil vigor.

The wind can also have an effect, e.g., if wind is blowing the flame off to one side.

Also the amount of flame, e.g., amount of propane sent to the burner.  Depending on your setup, it's not necessarily easy to get the flame at exactly the same strength every time you brew.

Perhaps the most significant factor, however, is the diameter of the boil kettle.  You probably didn't change your kettle between batches, but if you ever do, it's obviously something worth considering, as you'll see...  Forgive me for using a little simple mathematics, but if you usually use a kettle with a diameter of 18 inches, let's say, and now you switched to a kettle with 12 inches, this can have a huge effect based on the ratio of boiling surface areas.  Since A=pi*(R squared), you could compare 9*9=81 square inches versus 6*6=36 square inches and based on that the boiloff rate for the 12-inch kettle is 36/81 or less than half as much as the 18-inch kettle.  Quite a difference.
Title: Re: Is your boil-off volume reproducible?
Post by: denny on September 22, 2011, 02:58:22 PM
Several factors contribute, including:
Starting gravity

Hmmm, something I've never considered.  How does starting gravity affect boil off rate?
Title: Re: Is your boil-off volume reproducible?
Post by: Jimmy K on September 22, 2011, 03:40:34 PM
Several factors contribute, including:
Starting gravity

Hmmm, something I've never considered.  How does starting gravity affect boil off rate?

Dissolved sugars raise the boiling point of water, so higher gravity means the temperature of the boiling wort is higher. I was trying to figure out how much higher, but can't find a reference.
Title: Re: Is your boil-off volume reproducible?
Post by: denny on September 22, 2011, 03:43:58 PM
Dissolved sugars raise the boiling point of water, so higher gravity means the temperature of the boiling wort is higher. I was trying to figure out how much higher, but can't find a reference.

Based on my experience, I'd say that while that may be true theoretically, in the real world I've seen it make pretty much no difference.
Title: Re: Is your boil-off volume reproducible?
Post by: hopfenundmalz on September 22, 2011, 03:45:09 PM
Several factors contribute, including:
Starting gravity

Hmmm, something I've never considered.  How does starting gravity affect boil off rate?

Dissolved sugars raise the boiling point of water, so higher gravity means the temperature of the boiling wort is higher. I was trying to figure out how much higher, but can't find a reference.
If you search enough you will find the answer, and it is not much even for a 1.100 wort.  It doesn't even make up for the decrease in boiling temp. for where I live (at the nose bleed altitude of 900 ft above sea level).
Title: Re: Is your boil-off volume reproducible?
Post by: a10t2 on September 22, 2011, 04:00:58 PM
Dissolved sugars raise the boiling point of water, so higher gravity means the temperature of the boiling wort is higher. I was trying to figure out how much higher, but can't find a reference.

In a typical beer wort it's <0.5°C. The maximum would be ~1.5°C.

(http://www.sugartech.co.za/bpe/bpevsbrix.php?Temp=&Purity=&BrixImp=5;10;15;20;25;30;35;40;45;50;55;60;65;70;75;80;85;90&bpeImp=0.104230825774;0.342098276951;0.627265784901;0.907931408448;1.16682783387;1.42122237488;1.72291697267;2.15824819586;2.84808724054;3.94783993022;5.64744671591;5.04566066237;6.32102181372;8.72044244496;12.6692959972;18.6496723703;27.200377923;38.9169354728) (http://www.sugartech.co.za/bpe/bpevsbrix.php?Temp=&Purity=&BrixImp=5;10;15;20;25;30;35;40;45;50;55;60;65;70;75;80;85;90&bpeImp=0.104230825774;0.342098276951;0.627265784901;0.907931408448;1.16682783387;1.42122237488;1.72291697267;2.15824819586;2.84808724054;3.94783993022;5.64744671591;5.04566066237;6.32102181372;8.72044244496;12.6692959972;18.6496723703;27.200377923;38.9169354728)
Title: Re: Is your boil-off volume reproducible?
Post by: hopfenundmalz on September 22, 2011, 04:52:48 PM
Sean - I just was at that page. 

Where I live, water will boil at 210F, the calculator said 1.100 wort (24 Brix) will add 1.1 degrees C to the boil.  So if I do a Barleywine that gets me back to 210+(1.8*1.1)=211.98F assuming no big lows or highs are in the area.

Title: Re: Is your boil-off volume reproducible?
Post by: dmtaylor on September 22, 2011, 05:53:54 PM
It's true that gravity affects the boiling point temperature slightly, but the heat of vaporization of the water is barely affected at all, way down in the hundreds of a percent, i.e., negligible.  So yeah, basically it takes an extra minute or two to heat up your wort to boiling temperature, but once it's there, the amount of heat you need to add to boil it off is about the same regardless of boiling temperature.

Yes, that's right.  I'm an engineer.
Title: Re: Is your boil-off volume reproducible?
Post by: denny on September 22, 2011, 05:55:52 PM
Yes, that's right.  I'm an engineer.

And I believe ya!
Title: Re: Is your boil-off volume reproducible?
Post by: SiameseMoose on September 22, 2011, 08:25:29 PM
The only significant change in any variable is the humidity. I brew outside, but under a cover, so nothing extra entered the kettle, The burner is located at a walk-out basement door, which has a six foot wall right behind it which acts as a great wind shelter. I have a gas line plumbed from inside the house, so the pressure is the same. It's obviously the same kettle. In this case, I actually ran the flame higher for the batch with the lower boil-off. Finally, this is a frequent problem for me, and I've given it much consideration over the last few years, I'm convinced humidity is the factor at play here, and I was just looking for others experience with it.

Thanks for all of the replies!
Title: Re: Is your boil-off volume reproducible?
Post by: Malticulous on September 23, 2011, 12:33:49 AM
I brew a lot and still have not gotten my boil off perfected. I live in about the driest place in the US but it does get humid time to time. I end up topping off or just ferminting 6 gallons instead of 5.5 sometimes.
Title: Re: Is your boil-off volume reproducible?
Post by: hopfenundmalz on September 23, 2011, 01:36:14 AM
The only significant change in any variable is the humidity. I brew outside, but under a cover, so nothing extra entered the kettle, The burner is located at a walk-out basement door, which has a six foot wall right behind it which acts as a great wind shelter. I have a gas line plumbed from inside the house, so the pressure is the same. It's obviously the same kettle. In this case, I actually ran the flame higher for the batch with the lower boil-off. Finally, this is a frequent problem for me, and I've given it much consideration over the last few years, I'm convinced humidity is the factor at play here, and I was just looking for others experience with it.

Thanks for all of the replies!

On another forum,a guy in Canada was talking about the boil off rate he got in the winter when it was subzero (F) and the relative humidity was in the single digits.   That was a crazy amount.

Anyone ever hike in the desert at 108F and 8% humidit?.  Not that bad, dry heat and all.  Then you take a break in the shade, remove the back pack and start to get the chills from the evaporation off of your back.  Just saying humidity is a factor in this.
Title: Re: Is your boil-off volume reproducible?
Post by: dhacker on September 23, 2011, 02:02:03 AM
I'm having a hard time predicting my boil-off volume. Two consecutive brews with the same boil time, and the first boiled off 2.5 gallons, but today was only 1.5 gallons. As far as I can tell, the only major difference between the two sessions was the humidity. Today I brewed in an on-and-off drizzle, so saturated humidity. The previous session was about 60% humidity. Today I even turned up the burner intensity because I saw that the boil off rate was low. I have to find a way to get a more repeatable figure. Any hints?

I think everyone has some problem with this sometime in their brewing career. Several years ago I found a way to get real close to the final volume I was looking for. I threw out all the theories, formulas and guess work and installed a site gauge on my brew kettle. I also made 90 minutes my standard boil time. I put 13.5 gallons of pre-boil wort in the kettle, and end at 12 post boil. You get a feel for the personality of your system after a number of batches, so now I watch to see how much volume has gone out in the first 30 minutes. I can tweak the boil rate up or down slightly to end up at 12 when 90 minutes has elapsed. This way, the first 30 minutes is spent getting your final volume dialed in without screwing up the timing on your hop additions, etc.

Yes . . my boil off is repeatable!    :D
Title: Re: Is your boil-off volume reproducible?
Post by: tubercle on September 23, 2011, 04:38:27 AM
Let me try again.....

Why try to predict all of this using all the complicated science and formulas, consulting the Myan Calender (adjusted for the Moon phase), gravity calculations, and throwing in the current price of eggs in China while burning the feathers of a black chicken and rattling cat bones?

 Get a piece of wood - mash paddle or something  - and hold it upright in your boil kettle. Pour in a known amount of water, say 1/2 gallon, and take your trusty Barlow and carve a notch where the wet and dry meets. Pour in another known amount, say 1/2 gallon, and repete the notch.

As you boil away, occasionally put the stick in and see where you are at. Cut the flame down and let it settle a few seconds and take a measurement. Not there yet? fire up the flame. At your desired volume? Start cooling; open another beer.

 This takes away every variable, temperature, humidity, altitude, etc....100%  reproducible volume.

I know, expansion due to heat...bla, bla, bla.

Enjoy the brewing experience.
Title: Re: Is your boil-off volume reproducible?
Post by: tschmidlin on September 23, 2011, 05:21:32 AM
Anyone ever hike in the desert at 108F and 8% humidit?.  Not that bad, dry heat and all.  Then you take a break in the shade, remove the back pack and start to get the chills from the evaporation off of your back.  Just saying humidity is a factor in this.
I'm not convinced it is a huge factor.  I haven't done the math, but boiling will drive off more vapor than any effects from the humidity.  When you consider that at the surface of the boil the humidity is damn near 100% and all of that steam is going up and out because your kettle is uncovered, ambient humidity just doesn't seem likely to play a major role.

I agree with tubercle though, it shouldn't be a huge source of stress. :)
Title: Re: Is your boil-off volume reproducible?
Post by: Kit B on September 23, 2011, 02:15:47 PM
Let me try again.....

Why try to predict all of this using all the complicated science and formulas, consulting the Myan Calender (adjusted for the Moon phase), gravity calculations, and throwing in the current price of eggs in China while burning the feathers of a black chicken and rattling cat bones?

 Get a piece of wood - mash paddle or something  - and hold it upright in your boil kettle. Pour in a known amount of water, say 1/2 gallon, and take your trusty Barlow and carve a notch where the wet and dry meets. Pour in another known amount, say 1/2 gallon, and repete the notch.

As you boil away, occasionally put the stick in and see where you are at. Cut the flame down and let it settle a few seconds and take a measurement. Not there yet? fire up the flame. At your desired volume? Start cooling; open another beer.

 This takes away every variable, temperature, humidity, altitude, etc....100%  reproducible volume.

I know, expansion due to heat...bla, bla, bla.

Enjoy the brewing experience.

This is exactly what I do.
While several factors play a role, I find that this is really the only simple method to which I have access.
It is fairly predictable, except on days of extreme humidity or a lack thereof.
Title: Re: Is your boil-off volume reproducible?
Post by: davidgzach on September 23, 2011, 05:00:17 PM
Agree with the no-nonsense way of determing your boil volume.  The more you brew, the more you will get to know your brewery and the more consistency you will see.  I can now pretty much tell just by checking my boil kettle where I am and where I need to be.  I'd say I end up within a pint of each brew regardless of the above stated factors.

But I do like the stir paddle notch idea.  May have to incorporate that to idiot proof myself for the days I have too many homebrews......

Dave
Title: Re: Is your boil-off volume reproducible?
Post by: euge on September 23, 2011, 07:27:41 PM
Another way is to take a tape-measure and calculate gallons per inches. One can mark the inside of the kettle if desired or just use the tape-measure.
Title: Re: Is your boil-off volume reproducible?
Post by: Kit B on September 23, 2011, 07:42:46 PM
...Or, yard stick
Title: Re: Is your boil-off volume reproducible?
Post by: richardt on September 23, 2011, 08:23:47 PM
Using a sharpie to mark the long plastic stir spoon does NOT work.   ::)

It probably has something to do with the heat and/or acidity of the wort.
The marks basically come off when you stir the wort.
Title: Re: Is your boil-off volume reproducible?
Post by: tygo on September 24, 2011, 03:41:44 PM
Another way is to take a tape-measure and calculate gallons per inches. One can mark the inside of the kettle if desired or just use the tape-measure.

Yep, this is what I do.
Title: Re: Is your boil-off volume reproducible?
Post by: dbeechum on September 24, 2011, 03:44:15 PM
I have a spreadsheet that I plug the kettle height into and it spits back a number of gallons both pre and post boil expansion, calculates the final gravity if I hit my boil off numbers and tells me how much sparge water I need based on the target starting volume.
Title: Re: Is your boil-off volume reproducible?
Post by: jeffy on September 24, 2011, 05:34:46 PM
I fill up the kettle to the high dirt mark, boil for an hour and accept what's left.  It's usually about 10 gallons of beer.
Title: Re: Is your boil-off volume reproducible?
Post by: euge on September 24, 2011, 05:43:23 PM
I fill up the kettle to the high dirt mark, boil for an hour and accept what's left.  It's usually about 10 gallons of beer.

Fill my 80qt nearly to the brim and heat for batch-sparging. After it is all said and done I get about 12 gallons of beer for a long boil and 13 for a short boil.
Title: Re: Is your boil-off volume reproducible?
Post by: dhacker on September 25, 2011, 12:10:49 PM
Well . . I was able to prove that my "Reverse Reckoning" works no mater the original kettle volume.

Y-day I brewed the Tripel that had a  31 lb.  grain bill . . about all my mash tun wants to choke. For whatever reason my sparge water needed for a 13.5 gallons original BK volume didn't seem to fit. and I had to batch sparge twice . . or so my mistaken calcs told me. Long story short . .14.5 gallons in the BK. 1.5 hours later I was at 13 gallons. One hour to go, so hops went in, all other additions in, and 12 gallons at flameout. Nailed my OG @ 1.074.

I guess I pretty much have it down to a 1/2 gallon per 1/2 hr. boil off rate no matter how I try to screw it up.   :D
Title: Re: Is your boil-off volume reproducible?
Post by: oscarvan on September 27, 2011, 12:13:00 AM
Let me try again.....

Why try to predict all of this using all the complicated science and formulas, consulting the Myan Calender (adjusted for the Moon phase), gravity calculations, and throwing in the current price of eggs in China while burning the feathers of a black chicken and rattling cat bones?

 Get a piece of wood - mash paddle or something  - and hold it upright in your boil kettle. Pour in a known amount of water, say 1/2 gallon, and take your trusty Barlow and carve a notch where the wet and dry meets. Pour in another known amount, say 1/2 gallon, and repete the notch.

As you boil away, occasionally put the stick in and see where you are at. Cut the flame down and let it settle a few seconds and take a measurement. Not there yet? fire up the flame. At your desired volume? Start cooling; open another beer.

 This takes away every variable, temperature, humidity, altitude, etc....100%  reproducible volume.

I know, expansion due to heat...bla, bla, bla.

Enjoy the brewing experience.

This is what I do too.......BUT.....BUT...and it's a BIG BUTT........there is the amount the volume decreases as a result of cooling....so I leave myself and extra 1/2 gallon above where I want to be at boiling temp, and then when it cools down I get what I am shooting for.
Title: Re: Is your boil-off volume reproducible?
Post by: Will's Swill on September 27, 2011, 01:49:20 AM
Well, if you don't consult the Mayan calendar, then you might ending up dramatically changing your hop utilization as you try to fiddle with the boil volume.  But instead of doing a kabuki dance, why not plan to overshoot your boil-off target and then top up if needed?  That's what I do, but I generally have a good feel for what the boil volume looks like and I fiddle with the burner (though never my boil time) and I usually hit my volumes dead nuts.  5 gal exactly yesterday (to the accuracy of my measuring spoon).
Title: Re: Is your boil-off volume reproducible?
Post by: oscarvan on September 27, 2011, 03:24:35 AM
Well, if you don't consult the Mayan calendar, then you might ending up dramatically changing your hop utilization as you try to fiddle with the boil volume.  But instead of doing a kabuki dance, why not plan to overshoot your boil-off target and then top up if needed?  That's what I do, but I generally have a good feel for what the boil volume looks like and I fiddle with the burner (though never my boil time) and I usually hit my volumes dead nuts.  5 gal exactly yesterday (to the accuracy of my measuring spoon).

You measured out 5 gallons with a spoon?  :o
Title: Re: Is your boil-off volume reproducible?
Post by: Will's Swill on September 27, 2011, 12:28:24 PM
Yeah, a teaspoon - "One million, four hundred eighty-five thousand, six hundred two; One million, four hundred eighty-five thousand, six hundred three; What, honey? Crap, lost count..." No wonder it was so accurate...   ;)
Title: Re: Is your boil-off volume reproducible?
Post by: Will's Swill on September 27, 2011, 12:34:53 PM
Thinking about this a little more...  The ambient air conditions won't make any difference actually while boiling, but in the run up to the boil and during chilling it might.  Does it take longer to get to a boil on the days where you have greater boiling loss?  Perhaps cover the pot while heating to a boil and chilling.  Watch for boilovers while heating, of course...  I sometimes heat my wort this way - I use a remote probe thermometer with an alarm set to 195F to let me know when I'm close to a boil so I can remove the lid prior to any mishaps (wort boils around 202F here).
Title: Re: Is your boil-off volume reproducible?
Post by: denny on September 27, 2011, 03:48:54 PM
there is the amount the volume decreases as a result of cooling

4% is the ROT
Title: Re: Is your boil-off volume reproducible?
Post by: mainebrewer on September 27, 2011, 07:33:16 PM
I've heard and used the 4% ROT.
Wondering, is this a linear thing? For example, 212 degrees to 60 degrees is a 4% loss in volume. What would the percentage loss be at, say, 100 degrees?
I know I'm over thinking this, just curious.
Title: Re: Is your boil-off volume reproducible?
Post by: hopfenundmalz on September 27, 2011, 08:46:29 PM
More than you want to know.  From 32F to 212 F it is 1.0 down to .958.  4% works for me.

http://www.engineeringtoolbox.com/water-temperature-specific-gravity-d_1179.html
Title: Re: Is your boil-off volume reproducible?
Post by: mainebrewer on September 28, 2011, 12:51:49 PM
Curiosity satisfied, thanks.
Title: Re: Is your boil-off volume reproducible?
Post by: kgs on September 28, 2011, 01:21:46 PM
I have a wooden spoon marked in half-gallon increments with a laundry marker. the markings haven't faded in a year of brewing.

I way overboiled my first outdoor batch (a little over a year ago). since then I've become better at modulating it. but I do wish I had something on the propane line that would be the equivalent of the wooden spoon. indoors, the boil is easier to control on the range.