No Chill In The Kettle

[PostModern]

In partial answer to my question, I just read the abstract for a paper that tested a whole range of variables, pH, Ca concentration, temperature, wort gravity, etc on the isomerisation of alpha acids and found that at 70C, less than 10% of AA's had isomerised over 90 mins, as opposed to 90% in 30 mins at 100C. HTH

 

[Barge]

Nice research PoMo...who wrote the paper?

 

[Steve Lacey]

In partial answer to my question, I just read the abstract for a paper that tested a whole range of variables, pH, Ca concentration, temperature, wort gravity, etc on the isomerisation of alpha acids and found that at 70C, less than 10% of AA's had isomerised over 90 mins, as opposed to 90% in 30 mins at 100C. HTH

Good find PM. Is there a linky link?

I am also greatly interested in this question and have been wondering for some time about the effect of 0 minute hop additions on IBUs when the wort is left unchilled for an extended period. Finally this thread got me into some google action of my own and the first thing I came up with was this mildly relevant article:

Most relevant bit:

The fact that there is some isomerization (about 15% in whirlpool versus 35% in the kettle) of alpha acid means that not only hop aroma and hop flavor can be achieved, but also some bittering.

In other words, there is some isomerization of alpha acids after flame out, but you would probably need a lot of late hops for it to make much difference to your IBUs. There are a number of other interesting perspectives in that article. Thanks for making me find it. :icon_cheers:

 

[PostModern]

Looking through my google history, I think this is the article:

http://ift.confex.com/ift/2004/techprogram/paper_25787.htm

Maximum solubility of alpha acids in a pH 5.2 buffered aqueous solution was 90ppm. Hop isomerization kinetics examined over a broad range of temperatures showed a rate coefficient of 0.0153(1/sec) for atmospheric boiling conditions. At 70deg C, less than 10% of alpha acids were converted in a 90 minute boil. At 120deg C, only 30 minutes were required for 90% conversion, with subsequent loss of iso-alphas to degradation products following. Activation energy was determined to be 36.375 kJ per mole.

(my bold)

 

[Barge]

Just tasted the now 10-day bottled beer and it is spot-on for bitterness and aroma :chug: :beerbang:

Certainly no more bitter than Heineken, etc, so I'd say leaving the wort to cool in contact with hops does bugger all for alpha-acid isomerisation.

 

[Yob]

grumble, moan, bitch..

had some real issues yesterday with convections in the kettle, whirlpooled twice and it just wouldnt bloody settle down so I bunged the lid on it and left it overnight..

sprang out of bed this morning like an author hearing the phone ring and raced out the back to find the bloody kettle still quite warm to the touch, racked the brew into a FV.. 34'c :blink:

now in the fridge but I rekon it wont be cool until lunch time, that'll be 24 hours since brewed..

bloody thing...

 

[Yob]

Just found the advantage to kettle chilling... was about to make a DME starter and realised that I had a kettle full of the perfect wort just sitting there, going to boil up 1.8lt, chill and do a atarter overnight and pitch the lot tmoz afternoon

Hopes are high

Put the DME away fatboy, Target wort is in the hizzie

 

[Samuel Adams]

Interesting thread.

It seems that the wort won't cool as quickly and therefore add more bitterness if you NC in K
But it's not the end of the world, good to know !

 

[Yob]

it could also be the ambient temps here in Melbourne ATM.. I keep on picking days that are +30 to brew on.

The temp the next morning of the latest one I did in this method was ~24-26 so not too bad, a few hours in the fridge and pitched.

:icon_cheers:

 

[Rowy]

I'm with you Yob. Brewing on 30 plus days is not much fun