I found this graph from brewsupplies.com which tells the effect of adding hops at various times in the boil.
The graph seems to say this:
- Adding a hop about 7 minutes before the end of the boil will give maximum aroma. The aroma will start to disappear if the hop is left boiling for longer than 7 minutes, but the hop will start to influence flavour.
- Optimal time for flavour is boiling for around 20 minutes. After 20 minutes, flavour will start to disappear and bitterness will increase.
- After about 40 minutes the hop is bittering only, with maximum bittering effect around 60 minutes.
But what about flame-out? According to this graph, adding at 0 minutes - which many recipes do - has no effect on aroma, flavour, or bitterness.
I've always felt uneasy about adding at 0 minutes. My understanding was this: Add the hops when switching off the gas, leave for about a minute, transfer to the cooling sink and take out the hop bag [Edited - I incorrectly mentioned grain before], then cool the wort down. Maximum time the hops would be in for is 1-2 minutes.
So, is my interpretation of flame-out wrong? Or should I be following the graph and adding at 7 minutes rather than flame-out?