Lesson 2 - Hop Biology and Cultivation

We now know about what the hop plant is, as well as its appearance and composition. Let’s now discuss the varieties used in brewing.

Such is the rate of change in the hop market, that no one really knows how many varieties are currently being grown but the number is likely to be in excess of 250. These are grown in over 25 countries. It is not possible to differentiate these varieties into separate groups based on α-acids and essential oil levels. This is because very aromatic hops can also have high α-acids levels. We tend to use how they are employed in the brewing process instead. Below are the two basic groups.

• Bittering or high α-acid varieties are predominantly used to impart characteristic bitterness to the beer.
• Aroma varieties predominantly impart hop aroma.

Different varieties have differing effects on beer flavour and aroma. The point in the process at which hops are added also affects their contribution. Hops added at the start of wort boiling tend to only impart bitterness, as the volatile aroma compounds are lost. Contrastingly, hops added during fermentation or maturation (known as dry hopping), provide lots of aroma but very little bitterness (unless you add a lot!). Hops added towards the end of wort boiling or in the whirlpool can add bitterness depending on how long they are in hot wort and the degree of agitation. However, the amount of bitterness imparted is less than if they were added at the start of the boil. The flavour resulting from these additions is called late hop flavour or aroma.

Hops that are traditionally categorised as aroma hops usually possess a mild, pleasant aroma and a higher polyphenol content, as well as α-acid values well below 10%. In bitter varieties, an α-acid content above 10% is expected, and a strong, almost pungent aroma can be acceptable especially if they are to be processed to make bittering extracts. However, some of the new hop varieties do not fit neatly into either of these categories! For example, Mosaic is a hop variety that is predominantly used for its aroma, yet it has an α-acid content of almost 14%. When a hop variety possesses both a desirable aroma and good bittering potential (higher α-acid), it can be categorised as a dual-purpose hop.

The table below shows some of the broad hop categories. There is no official agreed categorisation of hops, so this is only for illustration purposes. There is nothing stopping you from using a variety listed as an aroma hop for bittering. Obviously, we need to add significantly more to achieve a target bitterness level, than if we use a higher α-acid variety.

Table: Hop categories

Aroma varieties can be used to impart bitterness to beer and bittering varieties can similarly provide aroma.

Hop variety popularity can be affected by many factors, but they must benefit brewers, growers and traders for long term success.