Lesson 9 - Brewing with Hops SAQ

**200 hL of Brand A is brewed at a high gravity. There are two hop products used to make the beer, a CO₂ hop extract with an α-acid content of 40% and T90 pellets with an α-acid content of 10%. Both hop products are added at the start of boil, with 2 kg of CO₂ extract added and 10 kg of T90 pellets being added.

The wort kettle has an overall hop utilisation of 50%. The brewery encounters an overall bitterness loss throughout the brewing process of 30%.

The beer is diluted from 7% to 5% ABV before packaging.

Determine the in-package IBU.

Response:

The first step is to calculate the total a-acid content of the wort:

CO₂ Extract: 2 kg x 40% = 0.8 kg of α-acid

T90 Pellets: 10 kg x 10% = 1 kg of α-acid

Therefore 0.8 kg + 1 kg = 1.8 kg of -acid is added to the wort kettle.

The next step is to calculate the amount of iso-α-acid at the end of the boil:

1.8 kg of a-acid x 50% kettle hop utilisation = 0.9 kg of iso-α-acid

Next, include the bitterness process losses:

If the bitterness process loss is 30%, then the amount of iso-α-acid retained is 70%

Therefore, the amount of iso-α-acid in the beer is 0.63 kg of iso-α-acid

Now, remember that an IBU is equivalent to 1 mg of iso-α-acid in 1 L of beer.

So, to calculate the IBU, you need to convert the total kg of iso-α-acid into mg of iso-α-acid (0.63 x 1,000,000) and convert hL into L (200 hL x 100).

So, the total IBU is 630,000/20,000 = 31.5 mg of iso--acid in a L of beer (or 31.5 IBU) before dilution.

Finally we need to account for the dilution of the beer before packaging.

If we divide the IBU by the high gravity beer ABV and multiply by the sales gravity beer ABV we will get the IBU of the beer in package

(31.5/7) x 5 = 22.5 IBU in package