At what point does one start adjusting hop addions?

Ingredients
1

What I am curious about is would one notice a difference between a beer brewed at 27 ibu’s, vs the same beer brewed at 23 ibu’s?
  If I make a recipe that calls for .75 oz @ 60 min and .4 oz @ 30 min. to hit my desired ibu’s, would one be able to taste it if I used 1 oz @ 60 min, and .5 oz @ 30?
  Along the same lines at what %AA difference would one start adjust the hop additions?
I assume it would depend somewhat on the beer style.
 
Dan

2

I am sure that others will have better answers than I but I remember reading that bitterness changes are not perceptible under 5 IBUs but this would obviously have a lot to do with the additions.

If you hop one beer to 20 IBUs with only a 60 minute addition and another beer to the same IBUs with only a 10 minute addition they will be very different even though, technically the IBUs are equal. Their bitterness may be equal but all other hop character derived from the beers would be very different.

I am not sure if I completely understand your question so I apologize if my response is lacking…

3

Your best bet is to brew both beers and do a side-by-side blind tasting. It will depend on the hop variety and freshness but I think you should be able to notice a slight difference between the two hop schedules.

4

Agree with goschmann, there has been a lot of taste testing out there that proves that generally people can’t detect a difference in 5 BUs up or down. You biggest difference is going to be in the flavor and aroma additions. Bumping up the amount of flame out or whirl pool hops is going to most likely be where you notice it most.

In the hopping schedule you are suggesting I think with a side by side test you would notice slight variastions, but nothing too terribly big. If you brewed one at 20 BUs and one at 30 then you will start noticing more marked differences.

[quote]  Along the same lines at what %AA difference would one start adjust the hop additions?

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I’m not sure I follow your question here entirely. The easiest way would be simply to plug the AA and boil times into your brewing software and make adjustments there.