Lawrence Brewers Guild

Rate is by the hour in boil off volume in a beer kettle.

In another post on the board, I stated that a volumetric measure is to the top of the vessel, quart jar or a 25 gallon kettle.

On my 25 gallon kettle it figures to about 1.26 inches per gallon. Measure the interior of the kettle to the lip (full mark). Take the interior measurement and divide it into the volume of the straight sided container gallons. Disregard the slight radius in the kettle base.

If you are using brewing software such as Beersmith, the software will give the starting volume and the finishing volume for your projected boil off rate. I believe that I have mine set at 9 percent per hour. Shrinkage is 4 percent but will not be used.

So the beginning volume for a 10 gallon brew is 14.62 gallons into the the kettle. Ending volume after the boil is 13.31 gallons ( 1 hour). 14.62 - 13.31 gallons is a difference of 1.31 gallons. Since I am going to measure the volume at 30 minutes (half of an hour) 1.31 / 2= .655 gallons boil off.

So, 14.62 - .655 = 13.97 gallons / 1.26" = 11.08" at 30 minutes if measured with your tape measure.

The kettle was measured at 30 minutes for a 1 hour boil and measured 11 inches so the firing rate was set close enough for the projected finishing volume.

Try this on your boil kettle and see how it works.

Here is the method I use to calculate my boil off rate:

R = (V1-V2)/V2*100

Where:
R = Boil off rate
V1 = Volume at the beginning of the boil
V2 = Volume at the end of the boil

Sorry, I couldn't resist.

For serials though, I took a measuring stick and poured one gallon of water at a time into my boil kettle and then just made tick marks on the stick. It's like they say, know thy system.