boil size?

[scottmc]

Hello everybody. I have a few questions concerning this dry stout recipe I got from my LHBS, I should of asked him while I was there but did not come to mind at the time, plus i like a couple different opinions on certain issues, anyway. So, my recipe calls for a 6gl boil, can i do a 3gl boil? because i only have a 20qt boiler, what will this effect? secondly, it says to boil for 90min, I thought 60min was the standard? the hop schedule are all the same time of 90min, can I change this as well? and finally it says Keg/bottling temp of 60f, does this mean storage temp, keep in mind this is an ale not a lager so can I ferment at 70-72f? Sorry for all the ?'s.

Cheers, Scott.

 

[david_42]

The utilization of the hops depends on boil time and wort concentration. You can do a 3 gallon boil, but you'll have to increase your hops by about 50%. Most boils are 60 minutes, but I've done boils from 30 minutes to 2 1/1 hours. If you do a 3 gallon, 60 minute boil DOUBLE the hops.

If this is an extract recipe, you could boil the hops for 30 minutes with 1/3 of the extract, add the rest of the extract & boil another 30 minutes.

The 60F is probably for the carbonation period.

 

[Baron von BeeGee]

The utilization of the hops depends on boil time and wort concentration. You can do a 3 gallon boil, but you'll have to increase your hops by about 50%.

Everything I have read indicates a 15-20% increase when doing a concentrated wort boil. Clone Brews specifically indicates for the all-grain recipes to decrease the hops by 15-20% (depending on the recipe), so it should work in reverse.

Decreasing the boil time from 90m to 60m plus going to a concentrated wort boil could certainly result in a 50% increase in hops, but a concentrated boil alone shouldn't.

 

[david_42]

Utilization for 90 minutes at 1.060: 0.226, for 1.120 0.132. Or about 71%.

Utilization curves are not linear in time or concentration and what most books use are approximations from some really old sources.

Concentrations for all grain don't vary much. Also, you are starting with a lower gravity which means better utilization during the first part of the boil, which is also the period when the isomerization is the fastest. Since most people can't detect bittering differences under 10 IBU, the 20% standard covers AG well enough.

 

[Baron von BeeGee]

Utilization for 90 minutes at 1.060: 0.226, for 1.120 0.132. Or about 71%.

Utilization curves are not linear in time or concentration and what most books use are approximations from some really old sources.

Your numbers come from Palmer, and if we accept them as up-to-date and plug them into the IBU calculation, also provided by Palmer:
IBU = [FONT=Verdana, Arial, Helvetica, sans-serif] AAU x U x 75 / Vrecipe
We will find that for the utilizations you've cited there is only about a 20% difference in the IBU's, hence my 15-20% number. In your 71% figure you've neglected to divide by Vrecipe. Adding 71% more hops in this case would result in a sorely disappointed brewer trying to achieve identical IBU's to a full-wort boil.
[/FONT]

Concentrations for all grain don't vary much. Also, you are starting with a lower gravity which means better utilization during the first part of the boil, which is also the period when the isomerization is the fastest.

Concentrations for all-grain vary from the weakest beer you brew to the strongest...from 1.030 to 1.100 just to throw some numbers out there. Those numbers are identical for a given extract recipe utilizing a full-wort boil and the same evaporation rates. Unless I'm not following what you're saying.

I think it's pretty clear that utilization is higher at the beginning of the boil and for a lower gravity.