Hops are a complex ingredient in beer, these little flowers that grow on vines can completely alter the way a beer tastes. There is a lot of involved biochemistry surrounding their interaction in the beer making process but it is good to know a little about what is happening when you use them because when you want to develop your own recipes, having some facts under your belt will be better than guessing how much to throw in.
The key things that we want to take from hops are to flavour and bitter the beer. To do this there are resins and oils that are produced in the lupulin glands that we want to utilize. There are of course other aspects to hops but these two things; the oils which will give the beer flavour and aroma and the resins which will bitter our beer are what we are most concerned with.
Hops are flowers that grow on vines, the hop vines are cut down and the flowers removed before being dried, just like how herbs are dried. This stabilises the hops so they can be stored, usually in vacuum packs under cold storage. When you buy hops they will usually have the date of the crop on the label so you know what year the hop harvest was.
There are a lot of hop varieties to chose from and you will notice when you come to buy them that they are usually labeled with an alpha acid %. This alpha-acid amongst other things is what makes up the hop resins. They are used to determine the hop bitterness and are expressed as the weight of alpha acid in relation to the weight of the hop flower itself. Most hops have an alpha-acid % in the range of 2 – 16%. So that means between 2 and 16% of the weight of the hop is the amount of bitterness resins that are available.
The reason hops are boiled in the wort for an hour or more is that these alpha acids are not very soluble and by boiling for such periods of time allows a chemical process called isomerization to occur.
An Introduction to How Bitterness is Measured
As you are probably aware certain beer styles have differing amounts of bitterness in comparison to others so the amount of bitterness needs to be measured. This measurement is called “International Biterness 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. You can find a complete guide to hop bitterness and how to work it out here.
Now, unfortunately, depending on where you come from or what recipe you have you could also have another measurement for hop bitterness which is “European Bitterness Units” (EBU). They are the same as IBU’s but only really differ in how they are calculated.