Ingredients: Hops

Hops provide a bitter counterpoint to barley malt's sweetness, as well as adding unique aromas and flavors to beer.


A brief history of gruit and hops 
(not on the syllabus - I just think its interesting)
 
In the middle ages, beer was flavored with gruit (grew-it or gr-root), a blend of spices and herbs such as rosemary, heather, ginger, spruce, and juniper. Blending and distribution of gruit was controlled and taxed by the Catholic church. In Germany, hops were first cultivated in 736 and found to be a good substitute for gruit. Around 1079, hops began to be used in commercial brewing.

In 1516, the German Reinheitsgebot, or Beer Purity Law, declared that beer could only be made from water, barley, hops. In 1710, the English Parliment taxed hops and banned the use of bittering agents other than hops. By 1750, hopped beers were popular across Europe.
 

Hops provide beer with: 

• bitter flavor to balance the sweetness of barley malt
• unique aromatic qualities
• an antibacterial effect which extends the life of beer

Hops are the cone-shaped flowers of a vine.
 

Botanically speaking, Humulus lupulus is a bine that is related to both nettles and marijuana, and the part used by brewers are called strobiles. For our purposes we can call them vines and cones. There are both male and female vines, but only the female plants produce cones.

The light green pinecone-shaped cones have papery petals and at the base of the petals are waxy, yellow lupulin glands, which contain the oils and acids useful to brewers.

Lupulin contains:

• Alpha acids which contribute bitterness to beer
• Essential oils which provide hop flavor and aroma.

Hop Growing

Hop vines grow back every year, and during the peak of the growing season they grow very rapidly. Commercial growers construct a trellis to support the vines, which can grow up to 20 feet tall. 
 

Hops are harvested by cutting vines off at the ground and passing them through a series of sorters to separate the cones from the leaves and stems. After harvesting, the hop cones are taken to an Oast House, where they are dried until they lose about two-thirds of their original weight. The dried hops are then either compressed into bales or processed into pellets or extracts.

Hops can be delivered in different forms.

Whole leaf hops are dried hops that have been compressed into bales. They retain all of their green leafy matter, which makes them easier to strain out during brewing. On the down side, the dried leaves absorb liquid.

Fresh, or Wet Hops are undried, unprocessed cones added to beer. Using fresh hops gives beer a fresh, bright hop flavor and aroma.

Pellets are dried cones that have been shredded, compressed, and formed into pellets. Shredding exposes the lupulin glads and removes some of the leaf material. The pellets are smaller and easier to store than whole leaf hops, but are slightly less aromatic. Pellet hops also tend to form a sludge on the bottom of brew kettles.

Alpha acids and essential oils can be removed from hop cones by using heat and solvents to create a liquid extract. 
Hop extracts keep for a long time and do not require filtering after their addition.
  

Hops are used in different phases of brewing to achieve different results.

Alpha acids contribute bitterness to beer, and they are extracted from hops by boiling. Boiling also causes some chemical changes in the alpha acids.

Boiling alters, or isomerizes, the alpha acids. Isomerization is the process which transforms a molecule is into another molecule made of the same atoms, but in a different arrangement.

The amount of Alpha Acid in Beer is measured in International Bitterness Units, or IBUs. One IBU is equal to 1 milligram of isomerized alpha acid in 1 liter of beer.

Isomerized alpha acids beer can react with ultraviolet (UV) light to produce a skunky smelling compound. These compounds are part of a family of foul smelling substances called mercaptans.
 
These compounds smell the same as the scent given off by skunks. People unfamiliar with skunks compare this scent to freshly brewed coffee. This beer fault is called lightstruck and it will come up again in the chapter about beer faults.

Clear glass bottles provide no protection against UV light. To combat lightstruck beer, MillerCoors has developed a hop extract that does not react to UV light. The brand name is Tetrahop. It contains hydro-isomerized alpha acids, which do not react to UV light.

Hop's essential oils add aroma to beer. These oils will evaporate during extended boiling, so aroma hops are added towards the end of the boiling period.

There are several other techniques to add hop aroma and flavor to beer:

First Wort Hopping

Hop's aromatic oils do not dissolve in water and evaporate during the boil. By letting the hops steep in the prior to boiling, the oils have time to react with oxygen to form compounds that will not be lost during boiling.

Dry Hopping
 
Hops can be added to the fermenter late in the fermentation cycle to increase the hop aroma in beer.

Randall

Beer is passed through a container of hops just prior to serving.

Different varieties of hops may be divided into two main types

Hop varieties containing high amounts of alpha acid are known as bittering hops, while hop varieties contributing desireable flavor and aroma properties are known as aroma hops. Some varieties of hops contain both desirable aromas and high amounts of alpha acids. These varieties are known as dual use hops.

IBUs, or International Bitterness Units, are a direct measure of the iso-alpha acids in a beer. Basically, 1 IBU is equal to 1 milligram of iso-alpha acid per liter of beer.   - See more at: http://craftbeeracademy.com/the-science-behind-hops-part-1-alpha-and-beta-acids/#sthash.eHv4AosZ.dpuf

IBUs, or International Bitterness Units, are a direct measure of the iso-alpha acids in a beer. Basically, 1 IBU is equal to 1 milligram of iso-alpha acid per liter of beer.   - See more at: http://craftbeeracademy.com/the-science-behind-hops-part-1-alpha-and-beta-acids/#sthash.eHv4AosZ.dpuf

Hop varieties grouped by their growing area, and each area has a general flavor profile.

European Hops

Hops from Continental Europe are commonly described as floral, earthy, or spicy.

Continental European hop growing regions include:

• Germany
• Czech Republic
• Belgium
• Slovenia
• Poland
• France

Of particular importance are hops from Germany and the Czech Republic.

Noble hops are classic hop varieties, and are named for the cities where they were originally grown. 

The Noble hop varieties are:

• Hallertau
• Spalt
• Tettnang
• Saaz

English Hops

English hops are commonly described as grassy, woodsy, or minty.

Some noteworthy English hop varieties are:

• Fuggles
• Challenger
• East Kent Goldings 
• Northern Brewer

American Hops

American hops are commonly described as having citrus or pine qualities.

American hops are grown in:

• Washington - 75% of American hops are grown in Washington State's Yakima Valley.
• Oregon
• Idaho

The major American varieties are know as the 3Cs: 

• Cascade
• Centennial
• Columbus

Other noteworthy American varieties are: 

• Amarillo
• Summit
• Citra
• Simcoe

Southern Hemisphere Hops

Australia and New Zealand are the major hop growing regions in the Southern Hemisphere.

Some important varieties are:

• Nelson Sauvin - Nelson is a region in New Zealand (on the north end of the south island). Sauvin comes from the Sauvignon Blanc grape that is grown in Nelson.
• Southern Cross
• Galaxy

The takeaway:

• Hops are a vine which produces cones which contain both alpha acids and essential oils.
• Hops varieties may be grouped by growing areas and hop varieties in these groups have similar flavor profiles.
• Hops are added at different points during brewing.
• Alpha acids provide bitterness and are extracted by extended boiling.
• The essential oils that provide aroma are volatile, and will be lost with extended boiling.

For additional research:

For The Love of Hops: The Practical Guide to Aroma, Bitterness and the Culture of Hops
 (affiliate link)

Stan Hieronymus

A Beer Beginner's Guide to Hops of the World
Homebrewing: A Guide to Essential Hop Varieties
Hops From a Land Down Under
Hop Growers of America
Hop Variety Descriptions
Hop extract use in beer
Hop FAQ