What are Hops?
Hops (Humulus lupulus) are a perennial plant of the Cannabaceae
family that also includes the genus Cannabis. In beer hops provide
bitterness to balance the sweetness of malt sugars, as well as flavors,
aromas, resins that increase head retention, and antiseptics to retard
spoilage. Often referred to as a “vine”, hops are actually a “bine”,
using a strong stem and stiff hairs to climb rather than tendrils and
suckers to attach. It is the flower of the hop plant that is used in
brewing. Hop flowers or cones resemble pine cones but are composed
of thin, green, papery, leaf-like bracts. At the base of these bracts are
waxy, yellow lupulin glands that contain alpha acids responsible for
bitterness and essential oils that give beer flavor and aroma. The plant
has separate male and female bines, but only the female bines develop
cones. If male plants are allowed to pollinate them, the flowers will produce seeds,
rendering them useless for brewing. Aside from their use in beer, hops also have medicinal application as a sleep aid. Hop filled pillows were once a common remedy for insomnia.
Day length during the growing season has a major effect on yield. For this reason the
majority of the world’s commercial hop production occurs between latitudes 35° and 55°,
either north or south of the equator. The largest producers of hops
are Germany, the United States, China, and the Czech Republic.
Other important growing regions include England, New Zealand,
and increasingly Argentina. Climate and soil conditions have a
major effect on hops. Varieties developed in one region will have
different flavor and aroma profiles when grown in another.
Hop plants sprout in the spring and die back to a cold-hardy
rhizome in the fall. During peak growing season they grow very
rapidly, up to twenty inches per week. Commercial hop growers
cultivate hop bines on V-shaped, wire and twine trellises that are
up to twenty feet tall. In spring, at the start of the growing season,
two to three young shoots are trained in a clockwise direction
around each horizontal length of twine. The harvest season begins
in August and continues into October with different varieties of
hops coming ready at different times. Harvesting machines cut the
bines and twine at the top and bottom and load them onto trucks.
They then pass through a series of sorters to separate the cones from the stems and
leaves. The cones are placed in a kiln where 140° air is circulated, drying the cones to
about 30% of their green weight. After cooling the cones are compressed into bales or
further processed into pellets or extracts.
Types of Hops for Brewing
Hops are available to brewers in whole-leaf, pellet, or extract form. American craft brewers
have also started using fresh, unprocessed hops to brew “harvest” or “fresh-hop” ales.
Each of these forms has advantages and disadvantages.
• Whole-leaf Hops – Whole-leaf hops are simply the dried hop
cones that have been compressed into bales. They are
believed to have greater aromatic qualities than the other
forms and are easier to strain from wort. However, because
they retain more of the vegetative matter greater volumes
must be used. They soak up more wort than other forms
resulting in greater loss to the brewer. Their bulk also makes
them more difficult to store and more susceptible to spoilage.
Hops can be generally divided into two broad categories, bittering and aroma. Those hop
varieties that contain high levels of alpha acids are called bittering hops because a lower
volume is needed to achieve high levels of bitterness. Those with lower alpha acid content
but higher levels of essential oils are called aroma hops. Beyond this broad division,
general characterizations can be made based on the traditional area of origin.
• Continental or Noble Hops – The noble hops originate in central Europe and are among
the most prized of the aroma hops. There are four noble hops, Hallertau, Tettnang,
Spalt, and Czech Saaz. These hops impart a smooth bitterness and spicy/floral aromas.
The noble hops are often used in lagers. Common descriptors for these hops include
spicy, black pepper, licorice, perfume, floral, and herbal.
• English Hops – The most traditional English hop varieties fall into the low alpha acid
aroma hop category. The most common are East Kent Goldings and Fuggle. Other
higher alpha English hop varieties include Challenger, Target, and Progress. Common
descriptors for the English hops include herbal, grassy, earthy, floral, and fruity.
• American Hops – Bright, fruity, and resinous, these are the signature hops of American
pale ale and IPA. The United States grows a number of hop varieties that can be
considered duel use hops, with high alpha acid content and pleasant aromatic qualities.
Commonly used American hop varieties are Cascade, Centennial, Chinook, Willamette,
and Amarillo. Common descriptors for the American hop varieties are citrus, grapefruit,
resinous, piney, fruity, and spicy.
Hops in the Brewing Process
Brewers use hops primarily to get bitterness, flavor, and aroma. Hops can be added at
several points in the brewing process to enhance one or the other of those things. While
most hops are added in the boil kettle, they can be added a various stages prior to and
after the boil as well.
• Kettle Hops – Kettle hops is the name given to those hops added to the kettle during
the boil. These include early addition hops for bitterness and late addition hops for
flavor and aroma.
• Bittering Hops – Bitterness from hops comes
from alpha acids found in the lupulin glands of
the hop flowers. The main alpha acids are
humulone and cohumulone and adhumulone. In
order to become bitter these acids must be
chemically altered, isomerized, by boiling.
Isomerization is a chemical process in which a
compound is changed into another form with the
same chemical composition but a different
structure. The percentage of the potential alpha
acid that is isomerized is referred to as
utilization. Because the length of the boil determines degree of utilization,
bittering hops are usually added at the beginning of the boil or with at least 60-
minutes of boiling time remaining.
• Flavor Hops – Hop flavor and aroma are derived from essential oils found in the
lupulin glands. These oils include humulene, myrcene, geraniol, and limonene,
among others. The flavors are released as these oils become dissolved into the
wort during the boil. However, these oils are highly volatile and are to a large
degree lost to evaporation. For this reason flavor hops are added with twenty to
forty minutes remaining in the boil. This provides a compromise between
isomerization of the alpha acids and loss of essential oils.
• Aroma Hops – Because the aromatic essential oils are highly volatile, aroma
hops are added in the last minutes of the boil to minimize their loss to
article written by Michael