Alpha acid isomerisation with concentrated wort

[podz]

Extract brewing, for those of you who don't notice which section this is in.

I have a 4 litre kettle at the moment, access to anything larger is impossible. I want to do a 20 litre batch of Dunkel.

Basically, I want to know if I can sufficiently isomerise the alpha acids in my bittering hops by boiling 1 kg of liquid malt extract plus 2 litres of water. That would put me at 3 litres volume inside of my 4 litre kettle. Is the pH level at this wort concentration out of range to isomerise the alpha acids or not?

Idea is to use a total of 4 kg of LME, but only boil one of them due to logistical cooking limitations. The other 3 cans will just be warmed in hot water and poured straight into the fermenter. Save the infection preaching for someone who gives a **** cuz it's not me

Honestly, I just want to know if I can isomerise my bittering hops (1.5 oz Hallertau) with this plan or not.

Thank you in advance for staying on topic!

 

[Yooper]

Isomerization used to be thought to be related to wort gravity, but it's been found out that it is not. Still, the IBU calculators take it into account.

What does occur, though, is the dilution factor. What I mean is this. If you are making a 23 liter batch, but only boiling three liters, the IBUs will be diluted.

The max you can isomerize is about 100 IBUs, and usually less than that. Even a beer like Pliny the Elder, which calculates out to sometime like 250+ IBUs has been tested around 80 IBUs. It has to do with the saturation of the wort by the hops oils, when the oils can no longer isomerize.

Anyway, since gallons is easier for me (sorry), and even though you probably won't get anywhere near 100 IBUs anyway due to the limits of isomerization, I'll use that as an example to make my math easier:

1 gallon of 100 IBU wort (from the boil) + 5 gallons of 0 IBU wort (no boil)= 6 gallons of 16 IBU wort.

That's why partial boils are often less bitter than a full boil- not because of wort gravity.

Since you're planning a dunkel, though, a very not-bitter beer, I think it's quite doable if you just remember the dilution effect of the IBUs.

You may want to boil about .5 KG of extract in 4L of water, because you'd be able to boil more liquid (that extract takes up a lot of room), and add the rest of the extract at flameout to pasteurize it and then top up with water.

 

[podz]

Thank you, Yooper. That was wonderful.

 

[flars]

Have you thought about boiling in batches. Partial boil with some of the hops and LME, pour to fermentor, and begin another partial boil.

 

[podz]

Have you thought about boiling in batches. Partial boil with some of the hops and LME, pour to fermentor, and begin another partial boil.

As I understand, correct me if I'm wrong, alpha acid isomerisation requires 60 minutes or we wouldn't have 60 minute boils as a standard to begin with. Monitoring multiple 60 minute back-to-back boils is not really gonna work for me. Even 45 minutes is out of the question.

Since I am only doing bocks at the moment, the low end of the IBU range for the bocks according to BJCP style guidelines is 16-25. From what Yooper explained, I should be able to easily achieve that with partial boils by adjusting my total volume downward a little bit here and there.

http://www.bjcp.org/2008styles/style05.php

I'm hoping to get a big brewferm electric kettle soon, but that will also require replacing some electrical circuits, etc. Nothing is ever as simple as it seems... Cooking outside on a burner is not an option, either, as our weather is complete **** for about 8 months out of the year.