Is hop utilization affected by boil volume and/or gravity?

[HopZombie99]

Hi lads, I'd like to hear some opinions on this technique I am going to try.
The math may not be correct for boil off loss, but I plan to top up with boiled water.
Target 6 gallon batch
Vessel 1: 4 (and a bit) gallons plain water for doing a 60 min boil of hops
Vessel 2: 2 (and a bit) gallons water for mashing 6.6 pounds of grain

I'll start by heating two vessels simultaneously. When vessel 2 get to temp, I'll turn the heat on low with the cover on to keep it at temp. When vessel 1 come to the boil, I'll add the 60 hop addition. After approximately 20 mins, I'll dough into vessel 2. The mash will go for 60 mins. When the boil hits 60 mins, I begin to bring the temperature down to about 165. Once the mash is finished I'll drain and sparge with the hop tea from vessel 1. After this is done, the plan is to bring back to a boil and finish the other hop additions.

The reason why I want to do this is I dont have a large enough vessel for a full boil and I think it'll shave about 30 minutes off the brew time.

The questions are these:

1) Does boiling hops in a smaller volume of water limit the IBUs you can get out of them?
2) If it does limit the IBUs, what is the hops to liquid ratio required for maximum utilization?

I understand by topping up with water, you dilute and by doing so lose some IBUs. BUT...
3) Is there something else at work that lower the IBUs other than simple dilution? e.g. electric charge loss or anything else crazy like that which would increase IBU loss over the rate of dilution?


Thanks for any insights.

cheers,

HZ99

 

[theveganbrewer]

Basic idea is as wort gravity goes up hop utilization goes down. Hops and wort together make a unique taste you don't get from just boiling hops in plain water.

I've always thought you need at least a gallon of wort per every half ounce of bittering hops. This was based off article I read citing alkalinity as changing hop flavor.

For example you could get 2 gallons of wort, calculate its gravity and use that to determine hop utilization then use that in conjunction with your mash addition and figure out the IBUs. I'm not going to do the math for you , but I think as long as you could get 2-3 gallons or so of wort to boil the hops in, you could figure final IBUs out.

You're going to need to adjust IBUs in the boil so that you account for worse utilization because of higher gravity and then also account for dilution after the boil.

There are charts out there to help, look at Palmer's how to brew online under hop utilization. I believe Palmer himself says you need enough extract to reach 1.030 gravity which is why his charts start at 1.030. He says to do so because of grassy flavors caused by boiling hops in plain water.

I think you can solve the small pot issue, but you won't be able to mash and do the bittering boil at the same time, you need to do at least part of the wort with hops.

 

[HopZombie99]

Anybody else have any thoughts?