Musing questions about boil off rate calculations

[MrStacy]

In order to get more accurate water calculations for mash and sparge, I know I need to have an accurate measure of my boil off rate (for my location). I know the easiest way to do it is put 5 gallons in the brew kettle, fire it up, boil for an hour, turn it off and see what’s left. But…. I notice in some of these calculators there is a consideration for “heat shrinkage”, so of course, in my mind, I should allow the boiled water to cool back down to approximate starting temp in order for it to be most accurate. And then…. I get to thinking “How big is the effect of starting water volume on boil off rate per hour?” For instance, let’s say I start with 1 gallon of water, in the boil kettle. I’m pretty sure 75% or better would be gone after an hour. So, for better calculation, should I start with around a volume I would typically start with in wort? (About 7.5 gallons). I’m probably over thinking this, so I’m hoping one of the seasoned brewers here can give me a good idea about the most sound way to calculate my boil off rate.

 

[Sandy Feet]

You are overthinking on the homebrew level. Much of it depends on the humidity. I live somewhere very humid. My boil off rate is about a gallon an hour. If you are at higher elevations or in the desert, yours will be higher. For eight gallons of water (full volume BIAB for five gallons), I would start guessing somewhere between 1 & 1.5 gallons depending on your climate, brew your beer, and see what happens. Make notes and use a recipe that could be flexible with higher or lower alcohol levels. If you haven't brewed all grain before, it is all going to be an experiment anyway.
A more challenging task is trying to figure efficiency.

 

[Megary]

I think it's hard to ever get an exact boil off rate. Lots of variables.

But...I agree with you that for a best guestimate, boil the amount of water that would normally be your "Pre-boil" volume for 1 hour. Cool, then measure.

 

[Herm brews]

First of all, welcome to the forum, there are many helpful brewers here who are ready and willing to offer advice and answer questions.
To start with, I would suggest going with the recommendation in the equipment profile setup on this site. Who wants to boil water just to figure out boil off rate? I want to brew beer. A good guess at boil off rate is 1 gallon per hour. Maybe try a scaled down version of some recipe you like, and figure your boil off rate while brewing. Make profile adjustments as you learn. After 4 years participating in this hobby, I’m still making little adjustments to process and equipment profile characteristics.
Most of all, have fun, rdwhahb.

 

[BarbarianBrewer]

Who wants to boil water just to figure out boil off rate? I want to brew beer. A good guess at boil off rate is 1 gallon per hour.

Completely agree! Start with 1 gal/hr and tweak it with each brew. My boil-off rate is between 1 & 1.25 gal/hr and since I brew outside outside in Wisconsin, temperature, wind and humidity all affect my boil-off rate slightly. I'd like to say I have a formula where I put in all those variables and calculate exactly what my post boil volume will be....but I don't. Someday, when I have more time, maybe I'll tackle that problem. But for now, getting close is my target.

 

[Megary]

Interesting. My boil off rate is .67 gal/hr. That's indoors, on a gas stove.

 

[Herm brews]

Before I moved away from my gas stove, I had my boil off set at .75 gal/hr. Now with radiant electric, I’ve had to bump up to 1.0 gal/hr. My new home is about 200 feet lower in elevation, but that’s negligible.

 

[Donoroto]

You can also measure the water volume just before boiling (say, 205 F) so you don't have to wait for it to cool.

Starting volume has no effect on boil off rate, assuming there's enough to last a bit over an hour and the vessel has a constant boil surface size (i.e. not conical but cylindrical).

 

[Minbari]

Depends on your setup. I use a steam condenser and my boil off is about 1/2 gallon an hour.

As you said, best plan is to fill with 5 gallons and boil for an hour. You will have some variance, but should be close.

For heat shrinkage, on 5 gallons. Not worth bothering with. You will see about a 4% difference from 60F to 212F.

I usually just shoot for the gravity i want. Not high enough? Boil longer. Too high? Add water after boil

 

[Megary]

Depends on your setup. I use a steam condenser and my boil off is about 1/2 gallon an hour.

As you said, best plan is to fill with 5 gallons and boil for an hour. You will have some variance, but should be close.

For heat shrinkage, on 5 gallons. Not worth bothering with. You will see about a 4% difference from 60F to 212F.

I usually just shoot for the gravity i want. Not high enough? Boil longer. Too high? Add water after boil

This is a great point. My recipes are designed for a 1-hour boil. So, if my pre-boil gravity is on target, boil length is an hour.

 

[The Brew Mentor]

There are many ways to get to your systems answer.
I'd start with exactly 1/2 gallon over your finished volume target. Then boil, chill and see how much more water you need to add to get to your target. This will account for boil off , shrink and kettle losses. Easy Peasy!
Cheers,
Brian

 

[Craigerrr]

You certainly don't want to over think your boil off rate, but if you wanted quick accuracy you could weigh the water before and after. Water expands and contracts, but it always weighs the same (physics)

 

[Ward Chillington]

Yeah...RDWHAHB and read this

https://www.brewersfriend.com/forum...-get-the-target-yield.10017/page-2#post-67167

And that's from a habitual over thiker! You're always going to be ballpark which is ok...just remember, wort WANTS to be beer!

 

[Minbari]

Yeah...RDWHAHB and read this

https://www.brewersfriend.com/forum...-get-the-target-yield.10017/page-2#post-67167

And that's from a habitual over thiker! You're always going to be ballpark which is ok...just remember, wort WANTS to be beer!

pretty much how I approach it. you have a target SG for the batch. if you end up with less than 5 gal or more than 5 gal, you want to hit your target.
My last batch was 4.5 gallons and right on target, this batch today was 4.5 gallons and way too high. so added some water and got it on the target.

 

[Zambi]

I usually just shoot for the gravity i want. Not high enough? Boil longer. Too high? Add water after boil

This!
I normally aim for too high gravity and dilute with cold (boiled) water after cooling the main amount. Helps to get to pitch temperature in a hot climate
And yes, IBU's will probably be a bit out

 

[Ozarks Mountain Brewery]

In order to get more accurate water calculations

one thing to note water is not wort, to be more acuate use wort to test `

 

[Ward Chillington]

This!
I normally aim for too high gravity and dilute with cold (boiled) water after cooling the main amount. Helps to get to pitch temperature in a hot climate
And yes, IBU's will probably be a bit out

Emphasis on that boiled part. Like I said, the wort wants to ferment but we want that to be with good yeast and not some other bad microbe or feril yeast that came in through the water. I've considered doing that method to speedup the chill but my system has given me good results so if it ain't broke.....ya know.

How has the Kveik been working out for you Z?

 

[Zambi]

How has the Kveik been working out for you Z?

I only have Voss and it's been a life saver from September to December, although I can now control temperature and thus have more options.
I like it best at real high temperature. 35-40 oC.
I recently found this interesting article: They seem to agree with me
https://www.deuxkanadierbraeu.com/post/voss-kveik-optimum-fermentation-temperature

And although Voss is real fast, I like to keep it in the fermenter for 5-7 days, carbonate for same amount of time and minimal 2-3 days in fridge before drinking

 

[Craigerrr]

As this is in the beginners brewing section of the forum I think we can assume that @MrStacy is relatively new to the hobby, and is making an effort to learn more about the hobby/craft. I think we need to be more constructive with our responses in this case. I don't think that "you are over thinking it", or "RDWHAHB", or veering off to a discussion on yeast selection are very helpful. There is so much to learn for the beginning brewer, and it is difficult to discern early on what to sweat, and what not to sweat. Learning the why and the how helps us all to know what are the more important aspects to focus on learning.

@MrStacy , your boil off rate is part of your total water calculation, but it will vary with your elevation, weather conditions, dimensions of your pot, and the amount of thermal energy applied. So you will never have two boils with exactly the same boil off rate. If I may, I recommend that you watch the following video. Early on for me, this was an "aha" moment as I was trying to understand total water calculations. I hope this helps you as much as it helped me in the beginning. I watched it over and over, and put pen (pencil actually) to paper to do my own calculations. In doing so I learned a lot about the brewing process.
Cheers!!

 

[Luiz-Roberto]

In order to get more accurate water calculations for mash and sparge, I know I need to have an accurate measure of my boil off rate (for my location). I know the easiest way to do it is put 5 gallons in the brew kettle, fire it up, boil for an hour, turn it off and see what’s left. But…. I notice in some of these calculators there is a consideration for “heat shrinkage”, so of course, in my mind, I should allow the boiled water to cool back down to approximate starting temp in order for it to be most accurate. And then…. I get to thinking “How big is the effect of starting water volume on boil off rate per hour?” For instance, let’s say I start with 1 gallon of water, in the boil kettle. I’m pretty sure 75% or better would be gone after an hour. So, for better calculation, should I start with around a volume I would typically start with in wort? (About 7.5 gallons). I’m probably over thinking this, so I’m hoping one of the seasoned brewers here can give me a good idea about the most sound way to calculate my boil off rate.

Yes, I think your plan is quite OK to determine the boil off rate. I´d say it dependes very much in the intensity (heat power) of you boil. Other factors are the exposed area i.e the diameter of your boiler, (the altitude, air humidity, moon phase, etc, are also important but not very much)! Assuming you´ll be brewing normally at the same place, just put 3 ...4 gallons of water in the boiler and let it brew for 1 hour (with the intensity you use while brewing). Wait so that it cools down to initial temperature and measure the lost volume- By the way, when you heat 1 gallon of water from room temp to boling temp it´s volume increase by approx. 4%