To extract bitterness from the hops they need to be boiled. Alpha acids in the hops are the primary source of bitterness and aren’t very soluble, boiling for around an hour is the most effective length of time to extract the alpha acids.
As you are probably aware certain beer styles have differing amounts of bitterness in comparison to others so this means the amount of bitterness needs to be measured. This measurement is called “International Bitterness Units” (IBU).
When a recipe is formulated the Alpha Acid % that is associated with the hops can allow us to work out how much hops are needed in that brew, according to what level of IBU is needed. In our recipes I have worked out the IBU for each brew so it falls in the range for the style.
Our steeped grain tea we made earlier can now be topped up the wort to a level suitable for the stock pot you are using. If it’s 12 litres for example a suitable level will be around 10 litres. The idea is to boil as much as possible without risking the pan boiling over and being unsafe. Now it’s full bring to a boil, turn off the heat and then the malt extract can be added, stirred in and thoroughly incorporated. Again be safe and leave plenty of head space in your pot so you can conduct the boil safely. You can now heat again and start a rolling boil.
Now the wort is boiling we can add the hops as directed by the recipe. The first hops added are boiled for an hour and provide the bulk of the bitterness as time passes add the aroma hops at the time indicated. During the boil leave your stock pot uncovered and keep an eye on it the whole time to ensure it doesn’t boil over.
Once the hour has elapsed we can start cooling and get the beer ready for fermentation.