Lesson 10 - Hops Final SAQ

***You are brewing your flagship lager. Your recipe states that there are three hop additions in the wort kettle, with the following requirements:

• Hop addition 1 – start of boil – utilisation is 35% and the α-acid is 13%.
• Hop addition 2 – half way through boil – utilisation is 25% and the α-acid is 13%
• Hop addition 3 – 16.7 kg of hops to be added 10 minutes before end of boil. The hop has an α-acid of 5% and a utilisation of 15%

The brew length is 250 hL and the target wort IBU is 30. The total IBU contribution from the first addition is 15 IBU.

a) If 4 kg of hops were added at the second hop addition, what IBU contribution will this give (show all calculations)?

b) How much iso-extract, with a concentration of 30% iso-α-acid and a utilisation of 90%, will be required to meet the target of 30 IBU?

c) Where and how in the process would you add the iso-extract?

Response:

There are a couple of approaches to the first part of this calculation.

Answer to a.)

Total iso-α-acid target is 30 x (250 x 100) = 750,000 mg/iso = 750 g of iso-α-acid

Hop addition 1 provides 15 x (250 x 100) = 375,000 mg/iso = 375 g of iso-α-acid

Hop addition 3

16.7 kg of hops = 16,700 g of hops

Which means 16,700/(100/5) = 835 g of α-acid

Which means 835/(100/15) = 125.2 g of iso-α-acid

Therefore hop addition provides (125.2 x 1,000)/(250 x 100) = 5 IBU

So, hop addition 2 needs to provide 30 – 15 – 5 = 10 IBU.

Option 1

Hop addition 2 is 4 kg of hops

4 kg of hops = 4,000 g of hops

Which means 4,000/(100/13) = 520 g of α-acid

Which means 520/(100/25) = 130 g of iso-α-acid

Therefore hop addition provides (130 x 1,000)/(250 x 100) = 5.2 IBU

This means that we are short by 4.8 IBU and the total IBU is only 25.2

Option 2

Total remaining iso-α-acid is 750 g (total) – 125.2 g (hop 3) – 375 g (hop 1) = 249.8g to come from hop 2.

Hop addition 2:

Mass of α-acid = (100/25) x 249.8 = 999.2 g

Mass of hop = (100/13) x 999.2 = 7,686.2 g = 7.69 kg of hops required.

Therefore 4 kg would be 3.69 kg short.

This means 3690/(100/13) = 479.7 g of α-acid

Which means 479.7/(100/25) = 119.925 g of iso-α-acid

Which means (119.925 x 1,000)/(250 x 100) = 4.80 IBU short

Therefore, the actual IBU achieved is 30 – 4.80 = 25.2 IBU

Answer to b.)

For the second part of the question, the calculation is as follows:

4.8 IBU x (100/90) x (100/1,000) x (100/30) g/hL = 1.78 g/hL, so therefore 1.78 x 250 = 445 g of iso-extract to be added.

Answer to c.)

For the third part of the question, the iso-extract is dosed prior to filtration, as not all the iso-α-acids are dissolved in the beer (90% utilisation), and the filter can then remove any undissolved particles. Any dosing equipment should be in an inert atmosphere. The extract is dosed directly in-line into the beer.