Boil Volume - Hop adjustment

[slowdrinker]

Hi All,
Planning an Adnams Bitter extract brew from GW's BYOBRA - the recipe give quantities for 19 litres, with hop additions at 0 and 80 minutes of the 90 min boil

I put them in to http://www.tastybrew.com/calculators/recipe.html with a 5 gallon (I believe its using US gals) for boil and batch volumes, and recorded the IBU.

My plan is to change the boil volume the 1.6 Gall (6 litres) I can manage, then adjust the hops amount till I got back to the same IBU.


Now the thing is, I was expecting with a smaller boil volume, to get less IBU from the same quantity of hops, but it has gone up.

At full volume boil, it was 38 IBU, with a 1.6Gal boil it was 43.

Am I interpreting things wrong ?

[prolix]

just divide all the quanities by 3.16 or /19 x 6.

no need to use a calculator divide by the length in the receipe times by the length you want.

[slowdrinker]

Just found this from a previous thread

viewtopic.php?f=3&t=36110&p=392922&hili ... me#p386221

very interesting link to the homebrew podcast - suggests changing the boil volume doesn't make any difference - I'll stick with my smaller stockpot for the moment then...

[beerandgarden]

Very interesting, this is completely contrary to what I understood. I've been playing around with BeerSmith and it shows the hops utillisation going down as the SG of the boil goes up. Also Palmer's famous book has a table of hops utilisation as a function of B.G. vs. time: http://www.howtobrew.com/section1/chapter5-5.html

How could these most trusted and widely used brewing resources get it so wrong without getting corrected as brewers discover their beers are way over hopped because of these calculations?

[Graham]

How could these most trusted and widely used brewing resources get it so wrong without getting corrected as brewers discover their beers are way over hopped because of these calculations?

Utilisation does decrease with increasing gravity, but not for the reasons that the formulae assume. The formulae assume that it is something to do with alpha-acid solubility in wort, but it has little to do with that. It is the protein in the wort that absorbs alpha acid and drags it out of solution with the break.

5kg of pale malt could make 24 litres of beer at OG 1050 or 12 litres of beer at OG 1100. Both beers will have the same amount of protein and will therefore absorb the same amount of alpha acid. The 12 litre beer should be twice the EBU of the 24 litre beer assuming the same quantity of hops have been added to both. If the 12 litre beer was then diluted to 24 litres, the EBU of the two beers would be identical. It is this that the formulae get wrong.

On the other hand, 10kg of pale malt would make 24 litres of beer at 1100. Twice as much malt equals twice as much protein which equals twice as much alpha acid absorbed, therefore the utilisation will drop. In this circumstance the bitterness of the 24 litre beer will be less than the others with the same quantity of hops. At face value it does seem that utilisation drops with increasing gravity, but it isn't the whole or the real story.

[kane]

5kg of pale malt could make 24 litres of beer at OG 1050 or 12 litres of beer at OG 1100

On the other hand, 10kg of pale malt would make 24 litres of beer at 1100.......In this circumstance the bitterness of the 24 litre beer will be less than the others with the same quantity of hops.

But in this case, if you're doubling the amount of pale malt, wouldn't you also double the amount of hops? And so getting the same utilisation as in the 5kg example?

[beerandgarden]

so back to slowdrinker's original question, I just played with http://www.tastybrew.com/calculators/recipe.html and I reckon it's getting it totally wrong. I plugged in a simple test recipe and compared the resulting IBU of the brew as I changed the boil volume. Here's what I got:

boil volume 5 gal (full boil): IBU 34
boil volume 4.9 gal : IBU 26
boil volume 4.7 gal : IBU 27
boil volume 4.5 gal : IBU 28
boil volume 4.3 gal : IBU 29
boil volume 4.1 gal : IBU 31
boil volume 4 gal : IBU 44
boil volume 3.9 gal : IBU 32
boil volume 3.7 gal : IBU 34
boil volume 3.5 gal : IBU 36
boil volume 3 gal : IBU 41
boil volume 2.5 gal : IBU 51
boil volume 2 gal : IBU 35
boil volume 1.5 gal : IBU 63
boil volume 1 gal : IBU 25

The IBUs go up and down like crazy with boil volume. This calculator obviously has a bug in it so you shouldn't rely on it. There is a great free spreadsheet application called Kit & Extract Beer Designer that I've found and I would trust - I have a link to it on my site here: http://beerandgarden.com/home-brewing-resources/. In this one, boil volume has no effect because it assumes a constant BG of 1.040 (not that that even matters perhaps..) and tells you how much ME to add to the boil to get that BG. So if you go by the new evidence that BG doesn't matter much, you can add as much malt as you want to your boil and keep hops qtys the same, but myself I'll probably just add 1 tin to the boil and get it reasonably close just to be on the safe side.