OG and Hop Utilization

[baggins22]

Hey Everybdoy,

I am having a hard time understanding this concept.

I am making a 5gl batch with 6lb of liquid extract and am trying to figure out my IBUs.

According to this site: http://www.howtobrew.com/section1/chapter5-5.html

"The recipe volume is 5 gallons. The gravity is figured by examining the amount and concentration of malt being used. As noted in the previous chapter, dry malt extract typically yields about 40 pts/lb./gal. Since this recipe calls for 6 lbs. of extract to be used in 5 gallons, the calculated OG = 6 x 40 / 5 = 48 or 1.048

But, since we are only boiling 3 of the 5 gallons due to of the size of the pot, we need to take into account the higher gravity of the boil. The boil gravity becomes 6 x 40 / 3 = 80 or 1.080"

It is the gravity of the boil (1.080) that is used in figuring the Utilization."

So, its the gravity of the BOIL (not the 5gl OG that is used for the utilzation)

i look up on this chart:

And calc my IBUs.

Now my question is this: since im getting IBUs based on a 3gal boil..when i mix in the rest of the 2gl of water, doesn't that dilute the IBUs?

Thanks!

 

[Theis]

Yes, adding the water at the end will dilute your gravity a well as your IBUs. There are ways to get around this, the easiest being a full wort boil. Another is to add the liquid malt extract at the end of the boil so that the high gravity of your wort isn't interfering with hop extraction during the majority of the boil. I recently saw an article in BYO that they called the "Texas two step" where they brewed the batch in halfs and then combined them at the end for fermentation in ordered to get around the problem of dilution and hop utilization.

If you are going for a 20-40 IBU beer it shouldn't be that big of a deal, just use a program like beercalculus (free) to calculate how much extra bittering hop needs to added to meet your goal IBU after dilution.
For me this issue really only come up when I am trying to make a bitter hop bomb with a small volume boil.

 

[billl]

If it's making your head hurt, just use one of the many online recipe calculators.

"Now my question is this: since im getting IBUs based on a 3gal boil..when i mix in the rest of the 2gl of water, doesn't that dilute the IBUs?"

of course, but the utilization calculations are separate from the IBU calc. Use the OG based on your boil volume and fermentables and the IBU calc based on the final volume in the fermenter.

 

[baggins22]

Thanks for the responses. i will look into just getting some software, but i wanted to make sure i understood the ideas behind the calcs.

billl - You mention that the utilization calcs and IBUs are not related, but how can that be?

IBU = AAU x U x 75 / Vrecipe

according to that formula i need to know my alpha acid units and my utilization rate to get my IBUs.

Thanks!

 

[bobbrews]

The utilization that you get from your hops will be based on the 1.080 +/- wort... not on the reduced OG after dilution. So if you're left with 50 IBUs after a 60 minute boil in 1.080 wort, and then you proceed to top off the 2.5 g end boil volume with another 2.5 g plain water, then you'll have 25 IBUs.

 

[baggins22]

Thanks, I think I am just going to try and boil my 5gl to start with... That should elongate most of these "issues".. Is that what most people do?

I guess I'm just getting stuck to using the directions that came from the beer shop (which say 3gl boil, then add the rest after)

It also say it should never sit in the first fermenter more than 6 days ( after being on this site, I think that's outdated information)

Thanks!