What's an accurate evaporation rate for the hour long boil?

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Tankard

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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?
 
11% is my evap rate on our gas stove in the kitchen.

I took my straight-sided 7 gal kettle and added 3 gals of water, boiled for an hour and measured. Boil off is based upon temp and surface area exposed to the air.

Use this experiment to calculate for beersmith.

Eric
 
I boil off about 6% in an hour in my turkey fryer pot and stove top set up. It really depends on how high your burner is going, and how dry it is in your climate.
 
Mine runs about 9% per hour. Whether I'm using a Bayou Classic SQ14 with 10psi regulator under a keggle or my crappy electric stove under a 32qt pot, it stays pretty consistent.

Chad
 
. . . . what do you have your Beersmith evaporation rate set at? How close is it, typically?
For my Bayou Classic SQ14 and an 11 gallon aluminum pot I have BS set at 15% for a 5+ gallon batch with .4 gallons lost to trub. When I do a 3+ gallon batch with the same equipment I use 18% evaporation rate and .3 lost to trub.

Mine runs about 9% per hour. Whether I'm using a Bayou Classic SQ14 with 10psi regulator under a keggle or my crappy electric stove under a 32qt pot, it stays pretty consistent.
Damn! I must be using too strong a boil :confused:
 
For my Bayou Classic SQ14 and an 11 gallon aluminum pot I have BS set at 15% for a 5+ gallon batch

Damn! I must be using too strong a boil :confused:


I have the same problem going, I was losing like 19 percent per hour, but that sq14 can get mighty hot, and I always put it on FULL BLAST when i use it, which is a mistake...

from now on I am going to go FULL BLAST until i get a boil, then back off A LOT till just enough flame to keep the boil...
 
I boil off about a gallon per hour (in Denver) from my keggle with a gently rolling boil. It doesn't seem to matter how much wort I have in the keg, so I have to fiddle the numbers to get accurate evaporation rates. That works out to be about 14% for 7 gallons of initial volume.
 
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.
 
I tested my evaporation rate today. I lost a little more than a gallon during the hour long boil (About 1.2 gallons). Do I just divide 1.2 gallons by the amount I started with (7 gallons). That's about 17.1 percent. Does that sound normal?
 
I too have always found the boil off in percentages rather odd at times. In the same pot a gallon of water will boil off just as fast if there are 5 gallons in it or 10 gallons. I've down sized a few recipes from 10 or 20 gallons to 5 gallons, and the collection values and the volumes came out odd a few times. I think it depends much more on equipment.

There might have been some sort of boil off perfect storm on my last brew. I lost close to 2 gallons in a little over an hour of boiling. There was a slow cooling process, so I would imagine I lost more than usual to evaporation. I found out after I was boiling that my roommates lent away the large plastic tub we have that I usually cool the pot in. Trying to cool a 30qt pot in the sink did not go well or fast. I had to top it back off, but it seemed to come out just fine, well despite it blowing the top off the fermenter.
 
For three brews, (for whatever reason) my boil-off has been 7% short from Beersmith numbers. Next time I plan to increase their numbers by that much in the pre-boil volume.
 
I tested my evaporation rate today. I lost a little more than a gallon during the hour long boil (About 1.2 gallons). Do I just divide 1.2 gallons by the amount I started with (7 gallons). That's about 17.1 percent. Does that sound normal?

From my experience, you are better off fixed volume per unit time, rather than a percentage. It sounds like you boil about 1.2 gallons/hr.


TL
 
I've always just calculated mine at 1 gal per hour. It always seems to work out better by using a fixed volume rather than a percentage. IMHO of course.
 
I have a decent idea where mine should be as the boil goes, up until I stick the immersion chiller in it. So I take note with 15 min left and if I need to, I crank up the flame, but I prefer a gentle "simmer" for my boils instead, as the wort darkens less. I'd rather end up a tad under volume and add boiled water I've got stored to get to volume, then aerate and pitch.
 
From my experience, you are better off fixed volume per unit time, rather than a percentage. It sounds like you boil about 1.2 gallons/hr.


TL


Exactly. The boiloff rate is related to the surface area of wort exposed to the environment, and the temp of the boil. A % implies that this will vary with volume, which it can't. Regardless of your volume, your boil off will remain constant in the vessel you are using, if you boil at a consistent temperature. My system is 7 gallons to 5.5 gallons @ ~212 every time.
 
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 don't think ED has a Blichmann and he is just pushing your button but .....
Did you buy one ED? ;)
 
I figure 3 gallons for boil-off, chill loss (contraction), and trub losses, so I usually boil 8-8.5 gallons (I am picky about not getting the break protiens in the fermentor). It is not really relative to initial boil volume as others have said. Pretty much flat rate for a normal batch.

No doubt there is a point where the curve swings rapidly, just not in the area us HBers are working.
 
Is trub loss generally the same regardless of 1, 2.5, or 5 gallon batches? Will trub amount effect ABV or Gravity, since its actually a solid (or are you precalculating in beersmith to compensate for trub)? Thanks...just getting back into brewing after taking a year break.
 
I boil off almost 2 gallons in an hour. I figure on almost 8 gallons into kettle, 6 after the boil, 5.5 into fermenter, and 5 into bottling bucket.
 
I have an automatic brewery that I've been using for 7 batches now. It is all enclosed in a attempt to retain heat during the mash, and to not get my basement all steamy when I brew (all electric). I have a duct fan that vents out the window. This time I started with 6.5 gallons before the boil, and after 60 minutes I was shocked to find I had lost 3 gallons! My OG was 1.080 and I didn't have a yeast starter ready. I have a bad feeling about this batch.

The difference between this batch and the previous 6 is that I took the lid off of the boiler for the entire boil. Before I would leave it on, but off to the side a bit so about ~30% of the boiler was uncovered. I don't know if the vent fan increases the evaporation rate when I have no cover on the boiler but I'm going back to covering it to avoid disasters such as this (I presume it will be a disaster, but I'll have to wait until I drink it to make sure).

Moral of the story: If you have an enclosed brewery contraption with a duct fan attached, don't boil without a lid :)

Maybe I'll try again without the lid, but not boil so vigorously and leave the duct fan off.
 
I have an automatic brewery that I've been using for 7 batches now. It is all enclosed in a attempt to retain heat during the mash, and to not get my basement all steamy when I brew (all electric). I have a duct fan that vents out the window. This time I started with 6.5 gallons before the boil, and after 60 minutes I was shocked to find I had lost 3 gallons! My OG was 1.080 and I didn't have a yeast starter ready. I have a bad feeling about this batch.

The difference between this batch and the previous 6 is that I took the lid off of the boiler for the entire boil. Before I would leave it on, but off to the side a bit so about ~30% of the boiler was uncovered. I don't know if the vent fan increases the evaporation rate when I have no cover on the boiler but I'm going back to covering it to avoid disasters such as this (I presume it will be a disaster, but I'll have to wait until I drink it to make sure).

Moral of the story: If you have an enclosed brewery contraption with a duct fan attached, don't boil without a lid :)

Maybe I'll try again without the lid, but not boil so vigorously and leave the duct fan off.

Don't forget that completely covering it traps the Dimethyl Sulfide instead of letting it boil out of the wort...
 
It's different for everyone and depends on many factors, including kettle diameter, boil strength, altitude, etc.

I lose 0.80 gallons per hour under a vigorous boil. For my partial mash process, I only lose about 0.20 gal to trub. So that makes things easy calculations wise :)
 
I was losing 0.9 gallon/hour in my 7 gallon aluminum turkey fryer. When I switched to a 15 gallon SS kettle, I started losing 1.75 gallon/hr. It just depends on your equipment.

I did a test run with plain water to measure my boil off. Then, I check it every time I brew to dial into an average.
 
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.

This.

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.


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.
 
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.
 
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.
 
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.
 
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.
 
I am fairly new to brewing and decided to do some 1 gallon batches to try out 4 different hops with the same wort. After I did the first couple of batches I was stunned at the water loss. I had used the percentage I used for 5 gal batches. But that percentage was not close in this case and I was left with ½ gal when I was expecting a gallon. That got me thinking that the amount of water that boils off is a constant for a specific brew pot.

After reading the many answers on this subject I was still left not really understanding what is going on with the amount of water that boils away when I brew. I was going to say evaporation but it turns out in science there is a difference in evaporation and boiling. We are not losing water through evaporation when in the boil. It also turns out that water temperate is the same for a simmer vs. a rolling boil. Closer you are to sea level the hotter your boil is going to be. Now the article talked about more heat the boil would be faster, like a rolling boil, but the article did not address if you lose more water at a rolling boil than a simmer.

I found a high school science write up on the subject which shed a lot of light. It also got me thinking how much altitude plays into boil time. Based on the fact that water boils at lower temperatures in altitude you might have to boil your hops longer to get the same IBU as someone who is down at sea level.

I am going to look to see if I can find a formula that provides an answer as I am sure one exists. If I find I will post. AT the bottom in quotes is the article write up I found.

The one thing that is clear is you should get the same amount of water loss using the same pot, and I am guessing the same heat resulting the same boil profile (rolling to simmer) no matter what the volume of wort you are boiling. Thus using a percentage is incorrect. Baselining your equipment boil off, keeping the heat the same, should provide a constant volume loss for planning purposes.

“As the temperature of the water increases, its vapor pressure increases. When the vapor pressure equals the atmospheric pressure on the liquid, the liquid will boil. At high altitudes, the boiling point of liquids is lower than at sea level. In Denver, Colorado, water will boil at about 94°C. Do not confuse boiling with cooking. Cooking pasta in Denver is a slower process because the water is at a lower temperature. Also, realize that water boiling rapidly is no hotter than water boiling slowly. The temperature of the water remains constant during the boiling process. And, the temperature of a boiling liquid never rises above its boiling point. No matter how much heat is applied, the liquid only boils faster, not hotter.

There are fundamental differences between evaporation and boiling. Evaporation occurs at temperatures lower than the boiling point of the liquid. Also, evaporation occurs at the surface of the liquid, whereas in boiling, bubbles of vapor arise inside the body of the liquid. For a bubble to form, the pressure of the atmosphere on the surface of the liquid must be overcome."


Added:

After researching some physics sites it is obvious there are a lot of variables in play. BTU output being applied, atmospheric pressure (including height from sea level), wind, ambient temperature, pot metallurgy and thickness, pot diameter.

To calculate it would change for each boil based on weather. I think the key is to figure out your heat source to get a consistent boil the way you want it. I prefer rolling boil. Then do a baseline on your pot with water. I chose to use a sick and mark the differences from start, boil start, completion of 1 hr. boil, cooled 80 degrees F. Then I used a volume equation to measure the actual boil off and shrinkage after boil off to 80F. I have a Blichmann Boilermaker 10 Gal. Using the measurements I calculated the following 0.72 gal of boil off then 0.24 for the shinkage from boiling to 80F. So basically 1 gal. So now I am going to test with a boil where I would like to have 1 gal of wort. Based on previous results the 1 gal of extra water sounds correct.

I live in Southern California near sea level (850 ft). Our temperatures are fairly consistant year round. If I wanted to get fancy I could baseline and measure barometric pressure and ambient temperature. Then as I brew I could see how those variables affect the outcome. Right now I am assuming they will not have a lot of affect and holding the BTUs being applied to get a consistent rolling boil is the variable I really want to control. IF I don’t get reasonable consistency I will look at other variables. But I know why many experienced brewers take wort sugar readings to determine if they need to continue boiling or have boiled too much and need to add water.
 
I boil off 1.5 GPH on my setup and gas valve position.......determine your boil off rate by experiment and use that.

The key is to make sure you use the same position for your gas valve on burner every time so you are adding the same amount of heat on each brew.....if your flame is higher or lower from brew to brew your boil off rate will vary.

What oyu are looking for is a predictable boil rate so you can plan accordingly on your preboil volume to get the proper final volume
 
The key is to make sure you use the same position for your gas valve on burner every time so you are adding the same amount of heat on each brew.....if your flame is higher or lower from brew to brew your boil off rate will vary.
In my opinion that sounds good in theory, but not in practice. There are too many other variables. Volume, ambient temperature and humidity the big ones. At a homebrew level it's more about the perceived intensity of boil; experience with your system. Not perfect, but the best we can do.
 
In my opinion that sounds good in theory, but not in practice. There are too many other variables. Volume, ambient temperature and humidity the big ones. At a homebrew level it's more about the perceived intensity of boil; experience with your system. Not perfect, but the best we can do.

I agree that those other variables do effect the boil off rate slightly...but the most significant effect on the boil rate is heat addition......make that consistent and you will be pretty damn close. In practice it has worked for me. "Perceived intensity" is not a measurable quantity and therefore cannot be used for consistency....at least by this brewer :mug:
 
I boil off 1.5 GPH on my setup and gas valve position.......determine your boil off rate by experiment and use that.

The key is to make sure you use the same position for your gas valve on burner every time so you are adding the same amount of heat on each brew.....if your flame is higher or lower from brew to brew your boil off rate will vary.

What oyu are looking for is a predictable boil rate so you can plan accordingly on your preboil volume to get the proper final volume

Agreed.

My pre-boil volume can vary as I use the SG and pH of the final runnings to determine when to end the sparge. I accept what I get. I use my gallon/hr rate as a rough predictor of when to measure OG - and then adjust accordingly.
 

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