BITTERNESS UNITS

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An important part of the art of home brewing is the correct timing and the additions of the right amounts of hops for your brew. This is to ensure you get the correct bitterness, flavour and aroma. This can get bloody confusing! Whilst various beer styles have generalised discriptions a lot is down to perception. There is a constant need to taste and compare ALL beers, both home brew and commercial, to try and improve your product. So here's how I reckon it works.
This is PART 1 on this so do some research as feed back and discussion on my guesswork is encouraged.

GOAL: To calculate the amount of hops required to give the correct bitterness levels for any given recipe.

Some Assumptions, Facts & Guesswork:

1.All brew recipes are for whole hops unless otherwise specified.
Therefore all calculations are for whole hops unless otherwise specified.
2.Hop untilisation, or the extract of bitternees from hops, varies with the boil time and the specific gravity of your boil wort. The higher the SG the less efficient is the hop utilisation. The longer the boil time the more efficient is the hop utilisation, up to a point. Boils times will be 60 minutes in this case.
3.For our purposes 2.7kgs of liquid malt extract is added 7.6 litres of water to begin the wort boil.
This will give us a:
specific gravity of the boil of 1.110
which in turn gives the following hop utilisations:

Length Of BoilHop Utilisation
15 minutes6%
30 minutes12%
45 minutes21%
60 minutes23%
> 75 minutes30%
4.Recipes should provide one or more of the following items about the hop varieties to be used:
(a)Alpha acid
(a)HBU or AAU
(a)BU or IBU
(a)Hop boil time
5.With this information we can calculate hop weight, alpha acid, HBU, IBU and hop utilisation.
6.Click here to open the hop calculations window. Print it and get a pad and pencil.
7.Assume we have 5 gallon (US) recipe. We wish to convert the hop amounts for 23 litres using hop pellets and retain the intended bitterness. The recipe has the following information:
3/4oz Hallertaur Hersbrucker - 60 minute boil - 3 HBU
1/2oz Saaz - 60 minute boil - 2 HBU
1/2oz Hallertaur Hersbrucker - 30 minute boil - flavour
1/2oz Saaz - 45 minute boil - flavour
1/2oz Saaz - steep - aroma
Using the Hop Utilisation Table we can deduce that:
3/4oz Hallertaur Hersbrucker - 60 minute boil - 23% utilised
1/2oz Saaz - 60 minute boil - 23% utilised
1/2oz Hallertaur Hersbrucker - 30 minute boil - 12% utilised
1/2oz Saaz - 45 minute boil - 6% utilised
1/2oz Saaz - steep - 0% utilised
No alpha acid was given but this can calculated since we have the weight and HBU.
Therefore Hallertaur Hersbrucker has 4.0% alpha acid
and Saaz has 4.0% alpha acid.
International Bittering Units (IBUs) can also be calculated for the 60 minute boiling hops using HBU:
3/4oz Hallertaur Hersbrucker - 60 minute boil - 10.3 IBUs
1/2oz Saaz - 60 minute boil - 6.9 IBUs
The IBUs for the 30 minute hops are calculated using their weight and previously calculated alpha acid:
1/2oz Hallertaur Hersbrucker - 30 minute boil - 3.6 IBUs
1/2oz Saaz - 30 minute boil - 1.8 IBUs
So now we can calculate how many grams of whole hops we need for 23 litres. But our pellet hops are Hallertaur Hersbrucker at 5.6% alpha acid and Saaz at 3.9% alpha acid. No problem, the formula takes care of the different alpha acids but we have to multiply the result by 0.85 to convert from whole hops to pellets. The result is:
15.6gms Hallertaur Hersbrucker pellets - 60 minute boil - 10.3 IBU
14.5gms Saaz pellets - 60 minute boil - 6.9 IBU
10.5gms Hallertaur Hersbrucker pellets - 30 minute boil - 3.6 IBU
14.5 Saaz pellets - 45 minute boil - 1.8 IBU

So do you agree with all this crap or what?

The above theory has altered the Total IBUs some some recipes. Check it out.