Finding boil off rate

[ozarks42]

Hi all,
I’m setting an equipment profile for Beer Smith2 and am attempting to determine a boil off rate. I’m hoping that by boiling 5 gallons of plain water it will get me in the ball park for a boil off rate. I realize there are a lot of variables, to many to have a perfect boil off rate for all circumstances, and I will need to fine tune as I go, but I need a start.

I have a 15 a gallon aluminum kettle with a 15 ¾” inside diameter.

Here are the figures I came up with from boiling 5 gallons of water.

Started with 5 gallons of plain cold water.

It took 34 minutes to obtain a vigorous boil with a propane turkey fryer.

Boiled vigorously for 90 minutes. (I plan to use the BIAB method with a 90 min boil).

At 200 degrees I had had 3 gallons of water left.

At 100 degrees I had 2.5 gallons of water left.
At 78 Degrees I had 2.25 gallons of water left.


Is it safe to use a 1.5 gallon boil off rate?

 

[Gavin C]

That's 2.75 gallons of boil off in 90 mins

1.83 gallons/hour

You're over thinking it.

Put a known volume in the pot, 5 gallons is fine

Bring it to boil with the lid on as you will during a brew

Take the lid off and boil it for 15 mins.

Allow it to cool

Measure the volume in the pot (call it V)

Boil off will be 4x(5-V)

 

[chickypad]

At 200 degrees I had had 3 gallons of water left.

At 100 degrees I had 2.5 gallons of water left.
At 78 Degrees I had 2.25 gallons of water left.

Something's not right here. Chilling 3 gal of wort from boiling to room temp you should lose about 4% or .12 gal (which I can vouch for as I do 3 gal batches all the time). No way you lost .75 gal to chilling so one of the measurements must be off. As Gavin said if you started with 5 gal cold and ended with 2.25 gal cold after 90 min your boil off rate is 1.83 gal per hr. That's on the high end but possible, my big pot is 18" across and I boil off about 1.5 gal per hr.

 

[ozarks42]

My measuring stick is piece of wood that I marked at gallon intervals up to 12 gallons. to come up with the location of these marks I poured 1 gallon of water in the kettle then marked it at the water level. Anything between the gallons marks is an estimate. I doubled checked my gallon marks before I started this process by pouring 5 gallons of water into the kettle one gallon at at time then checking the water level on my stick.

During this process I never placed the lid on the kettle, would this had made a difference?

I tripled checked each measurement along the way also.

I lost 2.75 gallons of water from pre-boil to cool down to 78 degrees from what I calculate.

 

[Gavin C]

During this process I never placed the lid on the kettle, would this had made a difference?

Yes, as you are losing water during the heating too.

4% shrinkage from boil to RT is pretty much a universal constant. Water will have a known volume per unit mass at any given temperature and pressure.

If you want to expend time and energy on working out boil off you need more accurate markings than 1 gallon intervals. I would mark it at 5,4.75,4.5, 4.25... etc

 

[ba-brewer]

my 15gal pot with a decent boil loses a little more than 1.5gal/hr and might get close to 1.8gal/hr with a very vigorous boil. I think it is better to under estimate your boil off rate a little as you can always add water if you boiled off to much.

 

[ozarks42]

I have attempted to set up a BIAB equipment profile in BeerSmith 2. This is my first try so don't be easy on me. Please take a look and let me know your thoughts and feel free to ask any questions about my equipment or brewing processing.