Lesson 10 - Hops Final SAQ

*** You have been given two hop varieties to trial in your brewhouse. They have the following properties:

The beer brewed in the trial must have a noticeable woody/floral hop aroma.

You have 10kg of T90 pellets of Variety A and 5 kg of T90 pellets of variety B. You must use up all of the T90s in the trial. To make up any shortfall in bitterness, you have  pre-isomerised kettle extract (PIKE) which is 34% iso-α-acids with an extraction rate of 70%.

The brew length is 100 hL and the hop utilisation at the start of boil is 35%; at the end of boil it is 15%. The target IBU for the beer is 30.

a)    When in the boil will you add each of the hop varieties and product?

b)    How much PIKE will you need?

c)    Describe two ways in which the hops and PIKE could be dosed into the wort kettle.

Response:

a)    The question states that the priority is to have a woody/floral hop aroma. Farnesene is typically found in Noble Hops and has a woody/floral aroma. Based on this it would make sense to use Variety A. To maximise the aroma, Variety A should be added as late as possible in the wort boil. Do not be misled by Variety B having a significantly higher total oil % as the majority of it is myrcene. Myrcene is very volatile and likely to be lost in the boiling process, so even though the total oil content is high and, it is unlikely to be noticeable in the final product. If we were able to, adding Variety A as a dry hop would be a better option for a woody/floral hop aroma.

As it is not likely to contribute the desired aroma, we would add Variety B at the start of the boil to maximise hop utilisation. PIKE is already isomerised so we would add that at the end of the boil with Variety A to minimise losses.

b)    We need 30 mg/L of iso-α-acids and we are making 100 hL of wort so we need 30 x 10,000  = 300,000 mg of iso-α-acids

Hop Variety A is being added to the end of the boil where there is a 15% utilisation and has 5% α-acids and we are using 10kg. So to calculate the mg of iso-α-acids from Variety A we do this:

10 × 1000 × 1000 × (5/100)  × (15/100) = 75,000 mg

Hop Variety B is being added to the start of the boil where there is a 35% utilisation and has 10% α-acids and we are using 5kg. So to calculate the mg of iso-α-acids from Variety A we do this:

5 × 1000 × 1000 × (10/100)  × (35/100) = 175,000 mg

So from the PIKE we need:

300,000 - (75,000+175,000) = 50,000 mg

PIKE has 34% iso-a-acids and has an extraction rate of 70%. So to calculate the amount required we need to do this calculation:

50,000 × (100/34)  × (100/70) = 210,084 mg or 210 g

c)    Any two of these methods could be used:

Method 1 is suitable for whole hops, pellets and extract. It is essentially about weighing out the required amount of hops and manually adding them directly to the wort kettle or whirlpool. Cans of extract have holes punched into them and are added to the wort in a basket.

Method 2 is suitable for pellets and extract. The hop products are manually prepared and weighed, then loaded into a chute above the kettle/whirlpool, which is automatically released into the wort. Alternatively, they are loaded into a separate container. This container is either automatically transferred into the kettle/whirlpool via hot water or wort, or the wort is circulated through the container. This dissolves the hop products as it does so, and the hopped wort returns back to the wort kettle/whirlpool.

Method 3 is suitable for pellets and extracts and involves conventional sized hop product containers being loaded into a separate container, which then automatically weighs the required amount of hops and automatically transfers it into the kettle/whirlpool.