How does one determine the boil size? - Home Brew Forums
Register Now For Free!

Home Brew Forums > Home Brewing Beer > Beginners Beer Brewing Forum > How does one determine the boil size?

Thread Tools
Old 10-25-2008, 07:14 AM   #1
Pelikan's Avatar
Oct 2008
Q Continuum
Posts: 899
Liked 11 Times on 10 Posts

So I've quickly advanced to messing around with online calculators in an effort to develop my own recipes. One of the main factors is boil size. So I'm wondering, does the size of the boil mean the volume after all the goodies are added, or the amount of water before anything is added?

I suppose I'm asking, how does one determine the "boil size" to plug into the calculator? For my purposes, I'm referring to extract plus grain.
Back to brewing! It's been too long!!

Reply With Quote
Old 10-25-2008, 11:41 AM   #2
Bob's Avatar
Nov 2007
Christiansted, St Croix, USVI, US Virgin Islands
Posts: 3,927
Liked 144 Times on 105 Posts

Size of the boil is how much fluid is in the pot when you turn the burner on.

That, combined with the amount of extract dissolved in the fluid, allows the calculator to estimate the hops utilization percentage, which determines IBU. Say you've got 6 lbs of dry extract, 1 oz of hops at 5%AA that you'll boil 60 minutes. With a 3-gallon boil, the gravity in the kettle is 1.090, and utilization is relatively low; you'll get 13 IBUs from your ounce of hops. Increase the boil size to 5 gallons, the gravity of the boil drops to 1.054, utilization increases, and IBUs rise to 18.

Basically, theory aside, you determine boil size by the largest volume you can boil without excessive fear of boil-over. For my kettle, that's 3.5 gallons. For others, it's 15 gallons! So measure how much you can fit in your kettle. You can safely boil between 60-70 percent of that volume. For example, my kettle is 5 gallons, and I can boil 3.5 gallons safely; that's boiling 70% of the kettle capacity.

You want a vigorous, rolling boil, you see. A simmer with a couple of big "blups" now and then won't cut it. Protein- and sugar-rich fluids at a vigorous rolling boil tend to boil over and make a hell of a mess. So the size of the vessel - and therefore the size of the boil - is based on containment.

You dig?

Fort Christian Brewpub
St Croix, US Virgin Islands

Reply With Quote
Old 10-25-2008, 04:35 PM   #3
Malticulous's Avatar
Aug 2008
St. George Utah
Posts: 4,146
Liked 72 Times on 57 Posts

Don't forget to leave room for late extract additions.
Everything is better with a beer.

Reply With Quote
Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
how can I determine post-boil gravity from a pre-boil gravity reading? snailsongs General Techniques 5 03-05-2009 04:42 PM
Boil Size jaa2m General Techniques 14 11-20-2007 01:50 AM
Boil size Cos Extract Brewing 13 09-16-2007 01:41 PM
boil size? scottmc Extract Brewing 4 11-05-2006 03:40 PM
boil size? rflach1 Beginners Beer Brewing Forum 3 02-08-2006 10:02 AM

Forum Jump