What are Hops?
Hops are one of four key ingredients in beer, alongside water, malt and yeast. They are a bine (not vine) that grows flowers filled with alpha acids and essential oils that brewers value for their impact in beer. They generally give a bitterness when added early in the brewing process, and some incredible aromas and flavours when added later. If that’s not reason enough to love hops, they also act as a preservative that improves foam and extends the shelf life of beer.
Hops are a member of the Cannabaceae family. The main commercial hop, Humulus Lupulus, originated in the Hallertau region of Germany as early as 700AD. Commercial scale production now occurs in many parts of the world including the United States, Australia and New Zealand.
The hop plant consists of a crown of rhizomes below ground, annual climbing bines above ground, and flowers (or cones) that are harvested annually. The rhizome crown is the perennial storage organ on the plant. It feeds the growth of the canopy and ensures the plant’s survival. The bine consists of hop shoots with hooked hairs. In spring, when the new shoots emerge, they are trained in a clockwise direction to climb the string. They provide the canopy and photosynthetic capacity to support flowering.
Hop growth stages
Since hops are photo-period-sensitive, the summer solstice generally marks the transition from vegetative growth to reproductive growth. The amount of vegetative growth ultimately determines how much the plant will yield, so it’s particularly important to manage plant health during this time.
Hops are dioecious, which means there are male and female plants. Only the mature, unfertilised cones of the female plants are harvested for use in beer, as they produce the greatest yield of acids and essential oils that brewers value for their bitterness and aromatic properties. Male plants are only used when breeders wish to hybridise and develop new varieties.
Hop harvest commences around March every year in the Southern Hemisphere and September every year in the Northern Hemisphere. It runs for approximately 4-6 weeks, and consists of:
- Cutting – Bines are cut from the top wire and at the base, loaded into trailers and transferred to the complex.
- Picking – Bines are hooked onto a conveyor that pulls them through the picking machine to remove the cones using wire ‘fingers’ arranged in rows on a circulating belt. The spent bines are shredded and used as mulch.
- Drying – Freshly picked cones have a moisture content of around 80%. This is reduced to 8-12% using kiln floors heated by a gas-fired plenum chamber that evenly disperses the heat. This can take between 8 – 12 hours.
- Conditioning – When dried cones leave the kiln floor there is still variation in moisture content, so they are dropped onto cooling floors and allowed to sit so that the remaining moisture redistributes more evenly.
- Baling – Dried cones are transferred to a hydraulic press and compacted into bales. Small windows are cut in the sides to allow for quality testing.
- Pelletising – Dried cones are milled into powder that is forced through a die to produce the typical pellet shape.
- Storage – Dried or pelletised hops can be cold stored for extended periods.
There are a number of environmental factors that determine where hops can be grown:
- Latitude - Good commercial production occurs 35° to 55° north or south of the equator.
- Temperature - low winter temps for adequate chilling, spring break of dormancy of dormancy needs to be sufficient, adequate spring growth is vital for good canopy development.
- Terrain - The majority of the world’s hop production occurs on flat to mildly undulating terrain.
- Soil - A light textured, deep soil that is well supplied with moisture but free of waterlogging is optimum.
- Wind - Exposure to strong wind can cause leaf damage and some loss of cone-bearing laterals.
- Water – Hops need to be kept moist during critical growth periods, which means irrigation is essential in areas of moderate to low annual rainfall.
Factors such as location, acreage, harvest capacity and harvest window all influence the analytical hop quality and their impact in beer. The standard batch-based measures of analytical hop quality tell a story from harvest and processing to storage.
Drivers of variability in analytical hop quality outcomes
Content provided by Hop Products Australia
How are hops used in beer?
Hops are used for various purposes in beer:
- Balancing the sweetness of malt by imparting bitterness
- Creating intense aromas and flavours
- Improving foam retention
- Extending the shelf life of the beer
Brewers design their beer recipes based on their perception of each hops’ performance in beer, which can range from floral and spicy to herbal and fruity depending on the methods and techniques used throughout the brewing process. Hops are generally categorised as either ‘bittering’ or ‘aroma’, although some are referred to as ‘dual-purpose’, which means they can be used for both purposes.
Bittering hops typically have a higher percentage of alpha acids and are added to the kettle early in the brewing process to kick-start a process called isomerisation which increases the amount of bittering compounds present in finished beer.
In 2012, more aroma hops were produced than bittering hops for the first time in recorded history. This movement began when Oregon State University’s U.S.D.A program released a hop named Cascade in 1972. It revolutionised the way the United States perceived beer, followed by the rest of the world.
Aroma hops typically have a higher percentage of essential oils. This makes a brewer’s choice of yeast particularly important. Apart from fermenting malt sugars to alcohol during brewing, yeast can change less desirable hop compounds into more desirable flavours and aromas through a process known as biotransformation. Biotransformation offers brewers the opportunity to be creative with new flavours and aromas as well as save money on hops since the right choice of yeast will amplify the perception of some hops flavour compounds, reducing the amount of hops required for brewing.
There are hundreds of compounds in hop oils. The most popular class of compounds present are terpenoids like geraniol or humulene, that possess strong sensory qualities. Geraniol can be transformed into floral aromas, while humulene can be transformed into spice flavours.
Another common class of compounds found in hops are thiols. They constitute less than 1% of hop oils but can be transformed into fruity flavours and aromas. Free thiols can be found in some hops, but the majority are inactive because they’re bound to protein-type molecules, which is why the biotransformation process is crucial to maximising fruity hop flavours in beer.
The timing of hop additions can also have a big impact on the release of hop compounds biotransformed by yeast. The difference in flavour based on the timing of hop addition is like night and day. To maximize the amount of terpenoids or floral and spice aromas and flavours extracted into wort, hops are added during late kettle boil or early dry hop. To maximise the amount of thiols or fruity aromas and flavours extracted into beer, hops are added during dry hop and late fermentation.
The world of hops is constantly evolving. Today, hops are available in a range of product formats including fresh hop cones, dried hop cones, traditional pellets, concentrated pellets, extracts, oils and liquids. As technology progresses, hop growers are adopting more innovative production processes to help brewers become more efficient, more sustainable and more profitable. This ongoing pursuit of hoppiness is a real labour of love, so next time you’re enjoying a cold beer, take a moment to appreciate the role hops have played in its creation.
