Adjusting (increasing) bitterness after primary fermentation

[Bosium]

OK, please bear with me, this is a bit of a read. I recently brewed a belgian blonde ale, a recipe I've been trying to perfect since I started brewing. It's a simple recipe, relying on the belgian yeast strain I chose for the esters and phenolics characteristic of belgian ales. It was meant as a 'clone' of De Koninck Blonde, if anyone here has had that. I mean the blonde ale, not the De Koninck pale ale (Bolleke), in case you were wondering. Recipe is below for those interested.

Now with a bit of tweaking using the pre-boil gravity, I managed to hit my numbers pretty much perfectly. I had a fast start to fermentation which actually went crazy over the 8 or so days of primary, enough to make me need a blow-off tube on a half-full 6 gal better-bottle. Never seen krausen go that crazy, but then I've always done my belgians in buckets up until now.

Fermentation has pretty much died down completely now by day 11, so I drew a sample and hey-presto, I hit my FG on the button. I tasted the sample, however, and found it not to be as bitter as I'd like to counteract the sweetness. I went back to beer smith and realised that my hop additions were specified as 'plugs' (whatever they are) and not leaf, like I used. This brought my total calculated IBU down from 25.1 to 22.2. It tastes even less than that to be honest, but the end result is the same: I would like to add some extra bitterness.

Now if the recipe hadn't attentuated as much as I aimed for (I suspected it might not have with the high mash temp), I was going to boil up a litre of water, cool it and add it to the fermenter (with enough sugar to make it 1.057 OG and enough hops to increase the total bitterness of the rest of the batch), as this would keep the same OG despite the addition of water, and would help the overall apparent attenuation, but I cannot do that now as my gravity numbers are perfect and I don't wish to mess with them.

I was thinking - could I draw off a litre of beer, and boil that up with some extra saaz, and then add it back to the fermenter to increase the bitterness? Is there any problem with boiling up already-fermented beer with living yeast in it (perhaps off flavours?).

I thought I could do something like this, please feel free to crit my mathematics:

14L @ 22IBU = 308 total bittering units.
If I remove a litre for the bitterness addition, that leaves me with:
13L @ 22IBU = 286 total bitterning units.

When I add the litre back (I'll have to add some water to account for the boil-off, when I do the actual boil, but lets say I return the same amount I remove from the fermenter), I will have 14L again, but I will want 25 IBU now. so:

14L @ 25IBU = 350.

Therefore, 350 - 286 = 64 bittering units which I will need to add within the 1L returned, which would work out to one litre at 64IBU. The 1L sample I draw off will already have 22IBU, so I will need to add 42IBU.

Beersmith tells me that if I have a 1L 'wort' of 1.011, and a boil volume of 2L (assuming I lose a litre during the boil), I will need to add about 3g of saaz 5.1%, boiled for 30 minutes, to achieve 47IBU (close enough). I'm not sure whether the fact that the 'wort' in this case is already hopped to 22IBU might affect the extraction of the new lot of hops, could anyone comment on this? I suspect it might, but I do not know how much to compensate for this.

How does that sound? Crazy?
Thanks in advance.

PS: PLEASE do not tell me to just leave it as is and RDWHAHB etc etc etc. I've taken that advice before and this time I'd rather try the scientific approach. I'm a stickler for hitting my numbers and settling for 14L of slightly unbalanced beer that I know isn't quite right just isn't how I roll


Recipe: (weight)

Belgian Pilsener Malt 85%
Demerara Sugar 5%
Czech Saaz (5.1% AA) @ 60mins 16.5IBU
Czech Saaz (5.1% AA) @ 30mins 8.5IBU
Wyeast 1762 (Belgian Abbey II / Rochefort)

Mash at 154.F for 60 mins, mashout to 170.F
Batch Sparge once.
Boil for 90mins with sugar added at beginning of boil.

Efficiency - 87%
OG - 1.057
FG - 1.011
AA - 80%
ABV - 6.0%

 

[david_42]

1. To increase bitterness, you boil some more hops.
2. No one can tell the difference between 22 IBU and 25 IBU.

 

[Bosium]

Thanks for the reply.

The figure of 25 is really academic, imagine it was 28 then, I'm fairly sure I can tell the difference between 22 and 28. For that matter I think there is a tangible difference between 22 and 25, if it means the beer is literally at the taste threshold of bitterness (which it is).

My question really is can I boil beer which has already been fermented without any ill effects?

 

[dobberson24]

Still no answer on this old thread. I'm thinking of doing this too since I've now come across a supply of fresh hops and want to add some bitterness to my already fermented beer. Will boiling a couple litres of beer with the hops then adding it to the finished product taste bad?

 

[thughes]

http://www.hoptech.com/products/iso-alpha-extract-2-oz

"This extract contains pure iso-alpha acids, which can be added to beer at any stage (post fermentation is best) to add up to 50% of its bitterness. (Not recommended for bittering your beer entirely since there are secondary benefits from wort boiling with hops.) However, our Iso-Alpha extract is useful for correcting an under-bittered beer and also for training yourself to judge bitterness levels.The Iso-Alpha extract can be added at any stage of brewing, but best utilization will occur if added just prior to bottling or to the serving keg. Simply add 1/8th of a teaspoon to 5 gallons of beer for each single IBU you want. Supplied in a 2 oz bottle with a dispensing cap, enough to add 16 IBUs to 30 gallons of beer."