Lesson 8 - Brewing with Hops

This section covers some basic hop addition calculations.

We pointed out earlier that BU and IBU are not the concentration of iso-α-acids in mg/L. However, for the purposes of hop addition calculations we assume that they are.

To calculate a basic hop grist (the amount of hops to add), you will need to know the following:

• The target IBU
• The percentage α-acids of the hop (or hops) being used.
• The percentage utilisation of the hop product at the addition point in question.

Hop grist for the kettle

“We need to produce 100 hL of beer containing 26 IBU, using a 10% α-acids hop product. The hop utilisation of the hop product is 25% at the addition point in question. What mass of hops (kg) do we need to use?”

So, to calculate:

If we accept that 1 IBU = 1 mg/L iso-α-acids, then we are looking for 26 mg/L of iso-α-acids.

We have 100 hL of beer. 1 hL is 100 L so that means in 100 hL we have 100 x 100 L = 10,000 L of beer.

Consequently, we need 26 mg/L x 10,000 L = 260,000 mg of iso-α-acids or 260 g of iso-α-acids.

If hop utilisation is 25% (remember, this means that only 25% of the hop product’s α-acids end up as iso-α-acids) then for every 100 g of α-acids, we get 25 g of iso-α-acids. So to calculate how much α-acids to supply, we do this calculation.

Only 10% of the hop product is α-acids so for every 100 g of hops we only add 10 g of α-acids. To calculate the mass of hops we need, we do this calculation.

The example above is very straight forward. A more complex example is covered in the video below. There is also a chance to try one yourself in the SAQ lesson which follows!

Another thing to consider is that the sensory bitterness is not just due to iso-α-acids. Polyphenols can affect bitterness, as can humulinones and hulupones.

When dry hopping beers, the leaf material added can absorb some of the iso-α-acids in the beer, pulling them out of the solution and reducing their level in the beer. The rate of removal depends on the dry hopping rate, method and the level of iso-α-acids in the beer. As well as removing iso-α-acids, dry hopping adds humulinones and α-acids.

Humulinones are 66% as bitter as iso-α-acids, and α-acids are about 10% as bitter as iso-α-acids. This means that dry hopping can add bitterness to the beer. We can measure humulinones, iso-α-acids, and α-acids using HPLC and estimate bitterness using this equation.

Bitterness = iso-α-acids + (0.66 x humulinones) + (0.10 x α-acids)

Earlier we covered how to calculate a hop grist. Calculating the amount of isomerised hop extract required is slightly different.

Iso-extract addition after fermentation

“The Iso-extract is supplied at a concentration of 30% iso-α-acids and has a utilisation of 90%. The density of the Iso-extract is 1.075 g/mL. We must add 5 additional mg/L iso-α-acids to 100 hL of a beer with 25 IBU. Provide the volume of extract required and the dose rate for dosing across the batch”

The fact that the beer already has 25 IBU is irrelevant. we need to work out how much iso-extract is required to add 5 mg/L iso-α-acids to 100 hL of beer. So we need:

5 x 100 x 100 = 50,000 mg or 50 g of iso-α-acids

We need 50 g of iso-α-acids and the extract is 30% so for every 100 g of extract we add 30 g of iso-α-acids. To get 50 mg of iso-α-acids, we need:

Utilisation is 90% so for every 100 g we get 90 g iso-α-acids. This means 50 g would come from:

As we are adding a volume rather than a mass, we need to convert the mass into volume using the density. For every mL we get 1.075 g so we calculate the volume required by dividing the mass by the density:

We have 100 hL to dose with extract, so dose rate is the required volume of extract divided by the volume of beer.

Congratulations! You have made it to the end of the hop lessons!