Isomerization and temperature

[OldRunner]

Is anyone reasonably clear on the effects of the isomerization process at varying temperatures?? For example, If I put 1oz of 15% Columbus in the boil for 60minutes, A certain amount of isomerization will occur. But If I place 4oz in at flameout and whirlpool for 20 minutes before applying a cooling method, it will be different.

So, My question is if I am making a large batch (20gallons) and the cooling process takes much longer than with a 5 gallon batch, will Isomerization continue to occur in the wort that is still hot (but no longer boiling) while it is "waiting" to be cooled?? I want to whirlpool the hops, but when I am done whirlpooling, the hops will continue to sit in hot wort and I want to determine whether to reduce the hops at flameout or determine if there is not isomerization at temps reasonably lower than boiling.

Im just not clear on this.

Thanks

 

[billl]

Join the club. Big breweries can take samples and determine actual IBU's for a variety of different procedures, but we're kinda left just going by taste. Based on the stuff they say, it looks like you get significant IBU contributions above 180 degrees and it tapers off rapidly from there. I've seen various rules of thumb that have the contribution dropping off about half for each drop of 10 degrees, but no hard data to back up that claim. Personally, I just drop the temp to 180 as fast as I can and then just leave it there for whatever length of hopstand I intend. I don't notice any bitterness differences that way, but honestly, I'm doing that mostly with IPA's that are pretty bitter to begin with.

 

[ColoHox]

You are describing a hop stand, and you do get additional bitterness from this process.

Full rate isomerization (as in what happens during the boil) will continue until the temperature drops below 175F. The utilization rate for hops added post boiling is around 10-15%.

 

[dstar26t]

You get 35% utilization in the kettle, best case with pellets. You get 15% utilization after flame out, best case with pellets. I assume a linear decrease from 15% to 0% from just off boil to 175F. Still experimenting though and the only measuring device I have is my palate unfortunately.