National Homebrew Day Giveaway - Enter Now - Weekend Giveaway!

Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > What's an accurate evaporation rate for the hour long boil?
Thread Tools
Old 05-11-2012, 09:50 PM   #31
Feedback Score: 0 reviews
tenbricks's Avatar
Join Date: Jan 2012
Location: Woodland Hills, Ca
Posts: 43
Liked 4 Times on 4 Posts


Originally Posted by Bobby_M View Post
Percent doesn't work for me. Boiloff is usually a fixed amount no matter how much liquid is in the same kettle. I lose about 1.5 gallons in 70 minutes in my keggle regardless if I start with 13 or 8 gallons.

Boiloff rate is determined by (heat in) = (heat out), the temperature remaining a constant 212. In practice I think heat out is almost entirely the boiling (vaporization) of the wort, much less so by surface area/size/shape. Heat in is determined by rate of propane burning and how efficiently it's heating the kettle, which will be a constant regardless of boil size. Thus, mostly it will be constant amount per time, not constant percentage.

Originally Posted by EdWort View Post
The Blichmann Boilermaker 20 gallon kettle will boil off 2 gallons in 90 minutes. I'm attributing that to the larger diameter of the kettle compared to a keggle.
I have the same pot, and see a bit more than a gallon/hour for 5 or 10 gal batches. Must not have the propane as high up as EdWort does.
tenbricks is offline
Reply With Quote
Old 05-12-2012, 12:30 AM   #32
Feedback Score: 0 reviews
Join Date: Oct 2011
Location: Florence, Alabama
Posts: 1,647
Liked 110 Times on 92 Posts
Likes Given: 510


Originally Posted by Tankard View Post
I'm tweaking the Beersmith settings and the default evaporation rate is 11%. So I would collect 7 gallons of wort and boil down to 5.5 gallons in an hour. That sounds a bit high. Has anyone ever calculated this based on a turkey fryer setup? I have a 30 qt aluminum pot.

Or, what do you have your Beersmith evaporation rate set at? How close is it, typically?
That is about what I am getting on mine (33qt tamale pot on a Bayou Classic)... about a gallon and a half (7 to 5.5) boiled off in an hour as opposed to a gallon (6.5 to 5.5) when done on the electric stove top. I have never used Beersmith or anything like that, so I have no idea about it's setup or defaults.
"Why did you.... what was the point of... how drunk were you when you decided this was a good idea?" - DMartin
wailingguitar is offline
Reply With Quote
Old 11-08-2012, 05:23 PM   #33
Feedback Score: 0 reviews
Join Date: Aug 2011
Location: Fishers, IN
Posts: 137
Liked 29 Times on 14 Posts
Likes Given: 36


I would agree with the arguments for a volumetric boil off rate related to the surface area of the water rather than a percentage of total volume.

I also would think that environmental conditions would have an impact on that number too.

A hot dry day would allow more water loss, versus a hot humid day would absorb less.

If you are always working indoors and have a relatively constant temperature and humidity, you are in the best case scenario.
hausofstrauss is offline
Reply With Quote
Old 03-16-2014, 08:48 PM   #34
Feedback Score: 0 reviews
Join Date: Jan 2012
Location: Warwick, NY
Posts: 17
Liked 1 Times on 1 Posts
Likes Given: 4


Listen to @blacklab and @bobbrews. The evaporation rate depends on the surface area of your brew kettle, the rate of boil (e.g., rolling boil), and to a lesser extent, the altitude. A percentage can be accurate if you always boil the same volume in the same kettle at the same rate, but as soon as you change one of these variables that percentage will be wrong.

If your kettle is tall and thin, it will generally have lower evaporation rate than a short and wide kettle. If you use a simmering boil, your evaporation rate will be much lower than a vigorous rolling boil. It doesn't matter how much you are boiling, because the boiling rate is the same (as judged from the surface - simmer, rolling, etc) and the surface area for the pot is the same.

If all we cared about is minimizing the evaporation rate (which would save water and energy), we might choose a tall, think kettle and simmer for an hour. But beer quality usually trumps these concerns, so the choice of brewpot and boiling rate is not so straightforward.
simchuck is offline
Reply With Quote
Old 02-28-2015, 10:47 AM   #35
Feedback Score: 0 reviews
Join Date: Apr 2013
Location: Ivanovo, Russia
Posts: 62
Liked 24 Times on 21 Posts
Likes Given: 19


I concur on the physics. The evaporation rate depends on the heat balance.

The amount of heat that goes in the kettle is your BTU's which are almost directly proportional to the flow of gas to the burner (how high you set the flame) or the electrical power supplied to the heating element.

The amount of heat that is lost to the surroundings via convection and radiation is proportional to the surface area of your kettle and its temperature. Even if your kettle is half-full, its walls are going to have about the same temperature from the bottom to the top as if it were full, because of the high thermal conductivity of the metal.

The difference between the supplied heat and lost heat is spent on the latent heat of vaporization, and that's what determines your evaporation rate.

How much of the actual wort area is exposed is not so much of the factor as it would be in the case of evaporation at room temperature.

That being said, the amount of wort in the kettle does not have a significant effect on your evaporation rate. Hence it is a fixed value rather than a percentage.
qmax is offline
Reply With Quote

Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
High Evaporation Rate spin02 General Techniques 10 07-16-2009 08:14 PM
Temperate/humidity on evaporation rate? chode720 Beginners Beer Brewing Forum 3 05-14-2009 10:07 PM
Evaporation rate? hopmadness All Grain & Partial Mash Brewing 10 03-25-2009 12:22 AM
help with evaporation rate killian General Techniques 11 08-11-2008 10:40 PM
Evaporation rate maltMonkey General Techniques 7 04-17-2008 05:38 PM

Forum Jump

Newest Threads