Learn more about hops and how to use them!

We have known for some time that hops are responsible for more than just the bitterness in beer. But it's only since the emergence of the craft beer scene in the USA that newer flavour varieties have been attracting more attention. Learn in this blog article why hops can make your beer bitter and fruity and use this knowledge to create exciting recipes!

To better understand the background to the different hop varieties, let's first take a closer look at the hop cone.

Only the female hops are relevant for brewers, as only the female form develops the lupulin glands, which are important for bitter and flavouring substances. These glands are located on the centre stem of the hop cone and develop during hop ripening in the form of cups in which essential oils and resins are secreted. This cup is then covered with a membrane to prevent the collected secretions from leaking out again. 

They contain the valuable resins and oils that are responsible for the bitterness and a large part of the flavour of the beer. These cups are protected by the outer leaves of the hop cone. 

This also highlights the advantage of hop pellets over whole hop cones. Hop pellets are nothing more than crushed and then pressed hop cones. This means that the resins and oils are evenly distributed in the pellet and can be utilised more effectively when brewing beer.

Hop resins can be divided into hard and soft resins. 

Only the soft resins are of interest to brewers, as they contain the alpha and beta acids of hops. While the beta acids also contribute to bitterness to a very small extent, it is primarily the alpha acids that bring bitterness to the beer. 

To do this, they have to be isomerised, i.e. converted. This is because only the iso-alpha acid, which is formed from alpha acid during boiling, is bitter. More on this later under ‘Boiling hops’.

Around 400 flavour-active compounds are known among the hop oils. The flavour possibilities are therefore wide-ranging. 

Two terpene alcohols in particular should be emphasised here. Due to their high solubility, linalool and geraniol can have a major influence on the hop flavour in beer, both when hops are added in the whirlpool and when cold. Both compounds have a floral, citrus-like aroma. Linalool smells sweet and is reminiscent of lavender and bergamot. Geraniol has a geranium-like and lemony odour. 

The dominance of the two compounds is due to their low odour and taste thresholds.

The flavour characteristics of the individual hop varieties can be viewed on the Barth Haas website under ‘Hop products’.

In general, hops for brewing purposes are divided into bittering hops and aroma hops. The former usually have more than 10% alpha acid, while the latter have more complex hop oils and usually have less than 10% alpha acid.

The classification of varieties is defined more by the intended use in the brewing process than by the ingredients, as all hop varieties inevitably contribute both bittering and flavouring substances.

Hop varieties that are primarily classified and used as aroma hops have a lower alpha acid content of less than 10% of the total alpha acid and a mostly high oil content. Examples of these varieties are the now very well-known Citra, or the Cascade and Centennial varieties. 

They are primarily described as having a pleasant flavour and the aforementioned low bitterness.

In recent years, high alpha varieties have become increasingly important on the market. These high alpha varieties include Nugget, Herkules and Hallertau Taurus. These are characterised by alpha acid contents of up to 22%, as in the case of Hüller Polaris hops. 

As the name suggests, these hop varieties are primarily used at the start of the boiling process and therefore for bittering the beer due to their high alpha acid content.

Depending on the intended effect, hops can be added at different points in the beer production process and have different effects on the yield of bittering and flavouring substances.

‘When hops are boiled for 60 to 90 minutes, their volatile essential oils are almost completely expelled’ (Nottebohm 2020). The time at which hops are added during boiling is therefore crucial.

At the beginning of the boil, the majority of hops are usually added with bitter/high alpha varieties to achieve the bitterness in the beer caused by the iso-alpha acid. 

The isomerisation of the insoluble alpha acid into soluble iso-alpha acid takes place relatively slowly. After 10 minutes approx. 10%, after 30 minutes approx. a quarter and after 60 minutes approx. a third of the alpha acid is converted into bitter iso-alpha acid. The majority of the alpha acid thus remains unisomerised in the wort. A longer boiling time does not lead to any significant increase in bitterness, but only to negative parameters, such as an increase in the heat stress and the excessive elimination of coagulable proteins. These lead to turbidity, among other things.

As the name suggests, bittering hops such as Taurus or Herkules are primarily used to adjust the bitterness of the beer. The timing of the addition of hops determines the bittering potential during boiling. Learn more about the background to wort boiling here.

When brewing beer, hops are typically added to the whirlpool with aroma hop varieties. 

It is advisable to add these hops at a temperature of around 80 °C, as the volatile aromatic substances of the hop oils no longer evaporate as much at this temperature and the alpha acid is no longer or hardly converted into iso-alpha acid. As a result, the addition of hops has little to no influence on the perceived bitterness of the beer. However, it can happen that the whirlpool function is weakened and thus more hot trub gets into the fermentation, which can lead to a scratchy bitterness in the beer.

By adding hops during the whirlpool, you can specifically release the flavour oils of the hops without actually making the beer more bitter. Learn more about the whirlpool effect after boiling the wort here.

Dry hopping is the addition of hops during the storage of beer.

When dry hopping, aroma hops are preferably used so that the volatile aromatic substances of the essential oils are no longer expelled and can instead significantly influence the flavour profile of the beer.

The hops are added during the storage of the beer, as the hop oils are dissolved by the alcohol produced during fermentation. Adding hops during the fermentation process itself entails many problems, such as the entrainment of volatile flavour compounds by the rising fermentation gases, which results in a loss of flavour. Furthermore, adding hops during primary fermentation can lead to stagnant fermentation or infection of the wort, as not enough alcohol has been built up as a ‘protective shield’ against bacteria.

The addition of hops in the cold area, i.e. during the storage of the beer, is ideal for gently introducing the flavour oils of the hops into the beer. This type of hop addition can be found in many fruity beer styles such as IPA's or session beers. Particularly popular varieties for hop tamping include Citra, Simcoe and Galaxy. These bring citrus, tropical fruit and red berry flavours to the beer.

-Jan Dubenkropp