Boil-off rate

[mrfocus]

In an attempt to help brewers, and to compare numbers between different brewers, I was wondering if you people could post the diameter of your boil kettle as well as your boil-off rate in number of gallons. These don't have to be exact numbers, but I would like to compile them and eventually do averages for different diameters of BKs.

PS. I know the boil-off rate depends on quite a few different things (the most important other factor would be the BTU of the power source, elevation counts as well, other smaller ones are ambient temperature and humidity, etc.) I would simply like to collect some data so people can see if they are close to what other people have.

Eventually this post will be edited to include averages for different sizes of BKs.

 

[mrfocus]

I'm trying to keep things seperated, so here are my results.

16" boil kettle and about 2 gallons of boil-off.

 

[lpdb185]

keggle (~16") boils off ~1.75g per hour.

 

[devilishprune]

I have a 15" diameter BK and get about 1.5 gallon/hour boil off

 

[ICanHazBeer]

15 gallon Megapot 18" - 2 gallons per hour boil off - using Bayou Classic SQ14 burner

 

[rjschroed]

bump cause i think this can be useful. I have a brand new 16" brew kettle on the way and would love to have an idea of what to expect. It looks like I should expect between 1.75 and 2 gallons of boil off. I'll let you know what I actually get as soon as I use it(my boilmaker buddy will be welding some couplers in it first)

 

[Henrythe9th]

19" 20gal pot 1 1/2 to 2 gal an hour depends on how hard of a boil

 

[mariojr]

15 gallon Megapot 18" - 2 gallons per hour boil off - using Bayou Classic SQ14 burner

I have the same setup and my boil off is around 1 3/4 gallons.

 

[Lonnie Mac]

15"/.88 EVAP/HOUR

Very gentle rolling boil...

 

[BrewBeemer]

Lonnie; you must be in a high humidity location of Texas also which gives you a low evaporation rate. On the island the average humidity of 62% to 68% plus my last BK keggle had only a 10" opening vs a 12". This alone reduces the open cross sectional area to 69.44%. My thinking which can be all wrong with reduced area has not created any bad results with the finished product on tap. Yet I still see keggles cut open with no top reduction in the kegs ID at all. I've given away used keggles with no tops at all just as fast as I receive them. I had a couple 75 minute boils at 1.0 gallon boil off if being careful wanting the maximum for net in the corny's

 

[Lonnie Mac]

Lonnie; you must be in a high humidity location of Texas also which gives you a low evaporation rate. On the island the average humidity of 62% to 68% plus my last BK keggle had only a 10" opening vs a 12". This alone reduces the open cross sectional area to 69.44%. My thinking which can be all wrong with reduced area has not created any bad results with the finished product on tap. Yet I still see keggles cut open with no top reduction in the kegs ID at all. I've given away used keggles with no tops at all just as fast as I receive them. I had a couple 75 minute boils at 1.0 gallon boil off if being careful wanting the maximum for net in the corny's

High humidity is so right my friend. I cut the grass today at about 95 degrees here in Bacliff/Galveston and thought I was going to literally die! I am getting to old for this! It's the first time in several years that I actually got the garden hose after myself afterwards to cool off because Moonbeam thought I looked kinda weird and ghost-white looking. (Whatever) It ain't even summer yet!

Yea, you are very correct. I am amazed at my boil-off rate sometimes. Although I do profess that my boil is let's say VERY gentle anyway... Just a moving surface with a good belch of bubbles every now and then, but it goes down on our high humidity days. I actually have a bigger boil-off in the winter time... I have never been an advocate of the "vigorous" boil, and sometimes think that that whole thing has been blown way out of proportion. 99% of my boils are 90 minutes in duration, thus the reason I gave the .88 per hour. So that is like 1.32 gallons evap in an hour and a half. Tell ya what, it is making some good beers too! Most brewing software that I have used is pretty good at calculating this by adding the temp of the day... I wish that they also had a humidity field that you could add too. I use Beer Tools Pro...

Good to hear from ya BB!

 

[kladue]

There should be a calculation for Vapor pressure somewhere that would let you input ambient temperature and humidity and predict water loss based on surface area exposed. I have not tackled that calculation in a long time and no longer have the tables to work from. It was used to calculate the evaporation from a swimming pool based on water temperature, surface area,ambient temperature, and humidity as a way to get to energy consumption of water heating and ventilation systems.

 

[ClaudiusB]

19" Kettle reduced to 4" vent

5.3 l/hr

I have never been an advocate of the "vigorous" boil, and sometimes think that that whole thing has been blown way out of proportion.

Info based on my flavor troubleshooting kit

Cheers,
ClaudiusB

 

[rcrabb22]

I have an 18" dia MoreBeer 15 gal kettle. I lose 2.5 gal to evaporation AND 1/2 gal to trub/deadspace. Also don't forget to take into account approx 4% shrinkage of wort when cooled

About the actual boil....

Listen to the Brew Strong Podcast from Jan 26, 2010 dedicated to the topic of wort boil. The boil doesn't have to be full out chaos but be strong enough to keep the wort circulating from bottom to top. IIRC this causes continued collisions of the proteins which helps them to bind to each other and become heavy enough to drop during rapid cooling as the cold break material.

I use muslin bags for my hops and my boil keeps them circulating in a circular motion from top of the kettle, across to the other side, submerging and reappearing on the surface at the point from which they started.

 

[chasman]

~15" aluminum stockpot (10 gal capacity) : 1/2 gal. boil-off last night
but... same pot : 1 gal. boil-off last brew
------------------------------------------------------------------------------
average boil-off for 2 brews = 3/4 gal for 60 min. boil

 

[CS223]

I've got the 44qt 13.5" stainless Bayou Classic pot that I'm putting the Camco 5500W ULWD element in and I'm looking for a boil off rate. Sure, I'll know when it's built but it might be a few weeks before then.

 

[LandoLincoln]

Keggle (approx 16" surface area)
185,000 BTU propane burner (Bayou Classic SP10)
Close to sea level (Chicago IL area)
Boil-off rate: Approx. 1 gal per hour

 

[Phyrst]

I've been contemplating this a lot lately as I'm getting ready to make the jump to all grain brewing. I'm a chemical engineer by trade, so thermodynamics is kind of second nature to me.

The dimensions of your pot and the size of your burner are going to be the major contributors. Humidity and elevation will have a small affect, but it will be negligible considering the number of BTUs you're pumping into your wort. The size of the pot matters because the a larger surface area of contact between the wort and the air will increase the vaporization rate. A short, wide pot will boil off more than a tall skinny pot.

My thought was to create some simple equations where you plug in the dimensions of the kettle and determine the boild off rate of a system by using some simple experiments to obtain some coefficients unique to your system. If I ever get around to it I'll be sure to post them.