BREW IT YOURSELF

Hop Varieties and Odour Compounds

In wine making, different types of grapes are used to produce a wide range of flavours and aromas. From a fruity Sauvignon Blanc to a robust Merlot, the chosen variety of grape plays a major role in how the bottled wine tastes. Similarly in beer, different varieties of hops play a fundamental role in the flavours and aromas found in your favourite ales and lagers. Some breweries will include the hop varieties used in a beer on the label or even in the name (e.g., the “Citra” in Citra Saison from Sleeping Giant Brewing Company).

Hops are the flowers or strobiles of the plant Humulus lupulus, a member of the Cannabaceae family of flowering plants. They are used in brewing beer to provide bitterness, flavour, and aroma (among other things like foam stability and preservation). Hops are grown by farmers around the world, with each region producing different types of hops, each with their own unique characteristics. New varieties of hops are regularly being developed by crossing different strains with the hope of producing a new variety that will appeal to growers, brewers, and drinkers.

For brewing, the key components of these hop flowers are the oils found within the lupulin—a yellow powder within the hop cones. The primary components of lupulin are alpha acids—cohumulone, adhumulone, humulone, prehumulone, and posthumulone. The boiling of wort in the beer-making process isomerizes these alpha acids which produces the bitterness found in beer. Anyone who has had a West Coast IPA would be very familiar with this bitterness, but essentially all beer has some degree of bitterness from hops. Depending on the types and levels of alpha acids in the variety of hops being brewed with, the bitterness produced in the beer may differ in its quality or how it is experienced by the beer drinker. For example, hop varieties with high levels of cohumulone tend to provide a harsher bitterness.

Further differences in hop varieties can be found in the other essential oils within the lupulin glands of the hop cones. Oils such as myrcene, humulene, linalool, caryophyllene, geraniol, citronellol, and many others can lead to a wide range of flavours and aromas (see Table 1 for an incomplete list). Each variety of hops has its own unique blend of these essential oils that give them the characteristics that are sought out by brewers. For example, many New England IPAs that are on the market feature the hop Citra, which is known for its strong aroma and flavour of sweet citrus and tropical fruits.

These essential oils that produce the incredible flavours and aromas are extremely volatile and are the main reason you should always ensure that your hoppy beer is kept cold, and any oxygen is kept out of the package (oxygenation of a beer will destroy these aroma and flavour compounds, and this will happen faster at warmer temperatures). Keep it cold and drink it fresh!

Hops varieties can be grouped by place of origin or by their common purpose in the brewing process. For brewing purposes, hop varieties are divided into aroma (primarily used at the end of boiling for aroma); bittering (primarily used early in the boil to produce bitterness); and dual purpose (can be used for both aroma and bittering). When it comes to place of origin, you might also see further distinction between older hops varieties (American: Cascades, Centennial) and newly created types (American: Mosaic, Citra). Furthermore, you might see the term “noble hops.” These are the classic European varieties that are commonly used in German and Czech pilsners and European lagers: Saaz, Tettnanger, Spalt, and Hallertauer Mittelfrüh.

With the large variety of essential oils within each type of hop, you can now consider the complexity that occurs when brewers blend hop types to create a beer. Combining wide ranges of essential oils can lead to unique and interesting flavours— but this is no easy task. Many different hop combinations have been discovered to work well by brewers, often using trial and error to find success. However, one brewer, hops researcher, and author from the USA, Scott Janish, has developed an online tool where brewers can calculate the profile that might result when combining different types of hops. If you are a homebrewer with a fondness for hoppy beer, check out the Hop Oils Calculator at ScottJanish.com along with all his other information on hops and IPAs.