boil off question

[itsratso]

when you consistently hit your pre-boil gravity but are coming up short on your final gravity that's because you've figured your boil off wrong, correct? just checking to make sure i'm looking down the right alley here.

 

[peterj]

Yeah that sounds correct. You can use this calculator to find out how much you're actually boiling off using your pre and post boil gravities. Or if you already know, just adjust your boil off rate in your calculations.

 

[catalanotte]

How's your final volume? I presume your volume to the fermenter is higher than anticipated as well? If so, just boil longer to hit your target OG. If this works, adjust for you lower boil off rate by reducing the sparge water volume for your next batch.

I was amazed at the differences between some estimates for a boil off rate and actual observations. The main factor is the surface area of you kettle, not the volume of the brew. A small difference in how turbulent the boil is can affect the boil off by 30 percent.

I have a kettle that is about 14 inches in diameter (11 gal) and I will boil off about .9 gal per hour. Doesn't matter if I have 3,6 or 9 gallons in the pot. Be careful with percent boil off numbers.

 

[itsratso]

thanx guys. i don't have a really good system for accurately measuring my final volume postboil, don't want to mess with it too much and get an infection. but yeah, i'm pretty sure it was too much - i was previously using a boil off calculator's estimate for my boil off. then, i foolishly decided to actually measure my 1 hour boil off with water. ever since i started using that number, my FG has been way off. i'm going back to the calculator's number.

 

[frettfreak]

thanx guys. i don't have a really good system for accurately measuring my final volume postboil, don't want to mess with it too much and get an infection. but yeah, i'm pretty sure it was too much - i was previously using a boil off calculator's estimate for my boil off. then, i foolishly decided to actually measure my 1 hour boil off with water. ever since i started using that number, my FG has been way off. i'm going back to the calculator's number.

? Why is that foolish? I did that and I hit my numbers pretty close. I would say I was only a little off but nothing to worry about. Liquid is liquid and since the wort is a lot of water I don't see why this would be an issue. I have done 4 batches on my new kettle and while I have had a few issues here and there dialing in my equipment profile, fg has been on the money.

 

[itsratso]

i shouldn't have said foolish, was just being kind of tongue in cheek. obviously it's working for you so stick to it. what i had was working for me and i went away from it. i would imagine that a calculator would give you a rough average for most conditions whereas when i measured my boil off in the middle of the hot humid summer it may not be close now that it is cool and dry out. or i might have screwed up my measurements

 

[catalanotte]

You hit the nail on the head, if it works, keep doing it that way. If you are interested in measuring volume more accurately, you can try an mark your kettle. I took a nail and etched marks at 5, 6, 7, and 8 gallons (cold) on the inside of my pot. That has helped considerably monitor pre boil volume and watch the boil off to post boil volume. I am going to add 1/2 tick marks before the next batch.

 

[BrewinBromanite]

^^ I do a similar thing, but I mark my mash paddle (big bayou classic paddle). Did this the first time I got my 10.5 gal kettles, and did an hour test boil with water as a baseline. I use the paddle throughout the boil, so I'm not worried about an infection if I measure the volume with it after the boil stops. As long as you maintain the intensity of the boil pretty consistently from batch to batch, you'll start to get predictable boil off rates and dial in volumes. Just trial and error - but find whatever works for you. If you get consistent results with your method - then stick with it.


Sent from my iPhone using Home Brew

 

[riderkb]

I get a lot of boil off, sometimes 1.5 gallon per hour. There is also a lot of variation in the rate depending on the phase of the moon, etc. So I quit trying to predict boil off. Now I just top off the kettle 10 min before the end of the boil.