Effect of late / dry hopping on bitterness (IBUs)

[The-Engineer-That-Brews]

Interesting lab test on the IBUs contributed by late and dry hopping: Brewing process Quality Control: Effect of Late and Dry-Hopping on IBU Value

The brew (Hackney Brewery 'Kapow!') had no hops in the boil but additions at flame-out, after 20mins, and in the FV.
Notes:
(1) the hop additions contributed significant bitterness (50-60 IBUs!) even with no boiling.
(2) the bitterness took about an hour to take effect after the hop addition.
(3) IBUs fell after pitching but the dry hop additions took it back up again.

For more details have a look at the link.

 

[The-Engineer-That-Brews]

Incidentally, I see that at least one testing lab in the US offers home brewers IBU testing for $20 per sample (see here). Is anyone aware of anything equivalent in the UK available to home brewers?

I've come across brewlab.co.uk but I'm not sure whether they cater to home brewers.

 

[dmtaylor]

The above looks like a false, non-standardized method of measuring IBUs, if it only takes 6-7 minutes versus ~30 minutes with a spectrometer. That being said.... if the result actually tastes like 60 IBUs, then this fact might not matter.

I would otherwise expect most of the IBUs in the experimental beer to come from the first two additions, at flameout prior to cooldown, then with the hefty 2nd addition around 80C. Later additions and dry hops should not contribute any actual IBUs. Perhaps this really is a 40-50 IBU beer, but not 60+.

Following is a super-simplified estimation formula I developed for calculation of post-boil hop additions, prior to chilling, while the beer remains around 80C. Try it and see how it matches up with your own experiences:

IBU = Sum [ g * AA% * sqrt(2 * time) ] / V / 7.5

where:
g = grams of each post-boil hop addition where temperature remains warm 70-80C
AA% = the alpha acid percentage for the particular hop addition
time = the amount of time in minutes that hop addition sees temperatures 70-80C
V = volume in liters

Sum together the first section for each hop addition, then divide by batch volume and 7.5, and you should have a reasonably accurate representation of IBUs from the late additions. The original method is described below. (For you folks in the UK, I included the conversion divisor of 7.5 which comes from dividing by 28 for grams instead of ounces, and multipication by 3.79 for liters instead of gallons.) Hope somebody out there might find this interesting or useful, and if not, well I don't care, it's worth about 2 cents.

 

[The-Engineer-That-Brews]

false, non-standardized method of measuring IBUs

Perhaps you missed that these were lab tests. Details of the measurement technology here: photometric-technology (cdrfoodlab.com)

 

[dmtaylor]

...which can be done in a few minutes by anyone. It's a shortcut method vs. the standardized method. Maybe it's good, maybe it's valid, I don't know. But certainly worth questioning in the name of science.

 

[The Baron]

IMO dry hopping does add bitterness whether that can be attributed to IBU contribution I do not know but it definitely adds to the bitterness in the beer. That is one reason I have cut down my dry hopping to smaller amounts and whirlpool mostly

 

[AJA]

Dry hopping causes a significant increase in the beers pH, which all else being equal will make the beer taste more bitter. I heard there is a sensory contribution to bitterness from hop aroma too.