Author Topic: Is your boil-off volume reproducible?  (Read 2884 times)

Offline SiameseMoose

  • Assistant Brewer
  • ***
  • Posts: 126
  • Cincinnati, OH
    • View Profile
Is your boil-off volume reproducible?
« on: September 21, 2011, 03:01:50 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?
_____________________________________________________
Rob
I named my brewery after my cat, Moose. He's Siamese.
Primary: Belgian IPA
Kellerbier (to be cask conditioned for Memorial Day)
Secondary: 3 different batches of Flanders Red, Lambic, Alt
Lagering: none
Kegs: 18, but not all in use
Bottles: Gazillions
Next up: American Wheat with pear concentrate

Offline Slowbrew

  • Senior Brewmaster
  • ******
  • Posts: 1657
  • The Slowly Losing IT Brewery in Urbandale, IA
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #1 on: September 21, 2011, 03:06:05 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
Where the heck are we going?  And what's with this hand basket?

Offline tubercle

  • Senior Brewmaster
  • ******
  • Posts: 1639
  • Sweet Caroline
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #2 on: September 21, 2011, 03:40:51 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.
Sweet Caroline where the Sun rises over the deep blue sea and sets somewhere beyond Tennessee

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3166
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Is your boil-off volume reproducible?
« Reply #3 on: September 21, 2011, 04:42:42 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.
Beer is like porn. You can buy it, but it's more fun to make your own.
http://seanterrill.com/category/brewing/

Offline euge

  • Official Poobah of No Life.
  • *
  • Posts: 7225
  • Estilo Casero
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #4 on: September 21, 2011, 07:28:22 PM »
Yes it does make a difference but not that bad. Mine is predictable.
The first principle is that you must not fool yourself, and you are the easiest person to fool. -Richard P. Feynman

Offline Kit B

  • Brewmaster
  • *****
  • Posts: 547
  • Kit B - Bottineau Prairie, MN
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #5 on: September 22, 2011, 07:24:47 AM »
Several factors contribute, including:
Starting gravity
Humidity
Intensity of boil
Surface area of boiling liquid
Wind
-    Head Cook & Bottle Washer    -
-      Bottineau Prairie Brewing      -

FBDU: Prairie & Northwoods Mobile Superintendant

Offline dmtaylor

  • Brewmaster
  • *****
  • Posts: 773
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #6 on: September 22, 2011, 07:37:14 AM »
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.
« Last Edit: September 22, 2011, 07:39:08 AM by dmtaylor »
Dave

"This is grain, which any fool can eat, but for which the Lord intended a more divine means of consumption. Let us give praise to our Maker, and glory to His bounty, by learning about... BEER!" - Friar Tuck (Robin Hood - Prince of Thieves)

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11670
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: Is your boil-off volume reproducible?
« Reply #7 on: September 22, 2011, 07:58:22 AM »
Several factors contribute, including:
Starting gravity

Hmmm, something I've never considered.  How does starting gravity affect boil off rate?
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe

Offline mtnrockhopper

  • I spend way too much time on the AHA forum
  • ********
  • Posts: 2884
  • Delaware
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #8 on: September 22, 2011, 08:40:34 AM »
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.
Jimmy K

Delmarva United Homebrewers - President by inverse coup when the old president ousted himself.
AHA Member since 2006
BJCP: B0958

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11670
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: Is your boil-off volume reproducible?
« Reply #9 on: September 22, 2011, 08:43:58 AM »
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.
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe

Offline hopfenundmalz

  • Official Poobah of No Life.
  • *
  • Posts: 4540
  • Milford, MI
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #10 on: September 22, 2011, 08:45:09 AM »
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).
Jeff Rankert
Ann Arbor Brewers Guild, AHA Member, BJCP Certified
Home-brewing, not just a hobby, it is a lifestyle!

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3166
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Is your boil-off volume reproducible?
« Reply #11 on: September 22, 2011, 09:00:58 AM »
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.

Beer is like porn. You can buy it, but it's more fun to make your own.
http://seanterrill.com/category/brewing/

Offline hopfenundmalz

  • Official Poobah of No Life.
  • *
  • Posts: 4540
  • Milford, MI
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #12 on: September 22, 2011, 09:52:48 AM »
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.

Jeff Rankert
Ann Arbor Brewers Guild, AHA Member, BJCP Certified
Home-brewing, not just a hobby, it is a lifestyle!

Offline dmtaylor

  • Brewmaster
  • *****
  • Posts: 773
    • View Profile
Re: Is your boil-off volume reproducible?
« Reply #13 on: September 22, 2011, 10:53:54 AM »
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.
Dave

"This is grain, which any fool can eat, but for which the Lord intended a more divine means of consumption. Let us give praise to our Maker, and glory to His bounty, by learning about... BEER!" - Friar Tuck (Robin Hood - Prince of Thieves)

Offline denny

  • Administrator
  • I must live here
  • *****
  • Posts: 11670
  • Noti OR [1991.4, 287.6deg] AR
    • View Profile
    • Dennybrew
Re: Is your boil-off volume reproducible?
« Reply #14 on: September 22, 2011, 10:55:52 AM »
Yes, that's right.  I'm an engineer.

And I believe ya!
Life begins at 60.....1.060, that is!

www.dennybrew.com

The best, sharpest, funniest, weirdest and most knowledgable minds in home brewing contribute on the AHA forum. - Alewyfe