calculation for increasing bitterness in batch

[BuzzCraft]

A guy in the local brewers group just brewed an AG batch that clocked in at 1.094 and 23 ibus. I don't know anything else about the recipe, mash temp, style, etc.

He was looking for advice on bumping up the ibus...it's a 5 gallon batch that went into the primary 2 days ago.

I suggested the following:
Add hops to 1/2 gallon of 1.030 wort (using DME), boil for 60 min, cool and add to fermenter.

He has 5% Goldings on hand. Beersmith says 2 oz in 1/2 gallon of 1.030 wort will deliver about 450 ibus.

I'm trying to figure out how many ibus this will increase his batch ibus: do you simply divide this out over the entire volume of the batch (which would now 5.5 gallons) then add the ibus that were there? This would suggest a final ibu value of around 100. Something doesn't seem right about that.

Since the solubility limit of isomerized alpha acids is around 100 or so (or has this been debunked?), does what I'm proposing still make sense or would he be better off with less hops in the boil?

Any thoughts?

 

[david_42]

Beersmith says 2 oz in 1/2 gallon of 1.030 wort will deliver about 450 ibus.

No, 100 IBUs is the practical limit for any volume of wort. Hop utilization proceeds to zero at high concentrations of alpha acids. None of the popular brewing software take this into consideration properly.

 

[Bensiff]

You can do what you are asking; however, take what David said as good advice. That leaves you with the problem of only getting 100 IBU's per volume into the wort so you have to add enough volume of the "hop tea" to raise the batch IBU's up to the desired amount and thus watering down the wort. This is complicated by the diminishing return as the IBU's rise, think of Pliny, if you calculate that recipes IBU's you get something like 300 IBU's when actual IBU's are around 95. That's a lot of hops to push it to that high a level. So, to do what you want you will have to do a lot of calculations. I would think you would want to drop the OG while pushing up the IBU's to try to get a realistic balance.

I just did the same thing with a Belgian after I discovered my scale was miscalibrated. Worked fine, but it was only adding 10 IBU's.

 

[BuzzCraft]

thanks for the replies, but it doesn't seem that anyone is reading the entire post....maybe cause it's long and rambling.

how about this: Starting with 5 gallons of wort at 23 ibus and adding 1/2 gallon at 100 ibus, will the final result be 41 ibus for the entire 5.5 gallon batch (at least in theory)?? or am i missing some other factor that affects the calculations when you "spread ibus" out over a batch?

 

[Bensiff]

Figure it by division. 100 IBU of 1/2 gallon into a 5.5 gallon batch would roughly give you 9 IBU's increase not 18.

 

[SC_Ryan]

Seems to me that hop extract would be the easiest most accurate way to add ibus

 

[Bensiff]

Seems to me that hop extract would be the easiest most accurate way to add ibus

It probably would be and was what I was going to use when I had this problem...then I looked at the price of the stuff.