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All About Hops

What Exactly Are Hops?

Hops are the cone shaped flowers of the hop plant cumulus lupus and are responsible for the bitter taste and much of the aroma in a beer. The lupin glands of the female hop flower are where the soft resins and oils used to bitter beer and impart aroma are contained. The hops resin is comprised of alpha and beta acids. The alpha acid in hops are the primary source of the hop bitterness and also acts as a preservative in beer. When heated in the brewing process, alpha acids are isomerized and form is-alpha acids. The amount of time that the alpha acid is subjected to the boil determines the degree of isomerization that occurs and the amount of bitter flavouring that is produced in the beer. The quantity of alpha acid present in a hop will determine the hops bittering potential. Alpha acid percentages vary dramatically between the different varieties of hops and are impacted by a multitude of outside factors such as storage packaging, age of the hop, storage temperature, oxidization, drying method and growing conditions. Unlike alpha acid, beta acid imparts only a small portion of the total bitterness in a beer, yet beta acids it is important because as the alpha acid bitterness breaks down over time during fermentation and storage, beta acid creates a sharper bitterness as oxidation occurs. Unlike alpha acid, beta acid does not isomerize during the boil and is primarily responsible for the hop aroma in a beer.

The History of Hops and Brewing

Before hops became commonly used in brewing beer was bittered and flavoured with spice and herb mixtures. The first documented link between hops and brewing is from 822 AD when a Benedictine abbot wrote a series of statutes covering the running of the monastery that included gathering sufficient hops for making beer. Evidence suggests that commercial hop cultivation began in northern Germany during the 12th or 13th century and that the Germans were exporting hopped beer from the 13th century onward. The first evidence of hopped beer being brewed in England is from 1412 and for a time English brewers produced both un-hopped “ale” and hopped “beer.” On April 23, 1516 the Bavarian Reinheitsgebot was put into effect declaring hops one of the three allowable beer ingredients (Yeast hadn’t yet been discovered). In 1710 the English parliament banned the use of non-hop bittering agents, at least in part to prevent brewers from evading the new penny-per-pound hop tax. From this point on hops became the dominant bittering agent in beer throughout the western world.

Main Varieties of Hops

Hops have been traditionally being categorised as either bittering or aroma. Hop varieties that contain high levels of alpha acids are called bittering hops. Those with lower alpha acid content but higher levels of essential oils are called aroma hops. Beyond the categorisation of either bittering or aroma hops can also be categorised 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.
  • 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.
  • American Hops – Bright, fruity, and resinous, these are the signature hops of American pale ale and IPA. Popular American hop varieties include Cascade, Centennial, Chinook, Willamette, and Amarillo.

Hop Forms for Brewing

Hops are readily available in whole-leaf, pellet, or extract form. Many brewers have now also started using fresh, unprocessed hops to brew new styles of beers over the traditional styles.

  • Fresh or Wet Hops – Fresh hops are green, unprocessed cones, often added to the beer within hours of harvest. Wet hops give beers an intense, bright hop flavor and aroma. However, because they lack the concentration that comes with drying, a much larger volume is needed to achieve the same result as from dried hops.
  • Pellets – To make pellet hops the dried cones are shredded, compressed, and extruded into pellets that resemble livestock pellets. The shredding process exposes the lupulin glands and removes a percentage of the vegetative matter, meaning smaller volumes can be used in the brewery. Their lighter weight and compressed state also makes them easier to store and less susceptible to spoilage. On the down side, they tend to lose some of their aromatic quality in processing and they create sludge at the bottom of the brew kettle that can be difficult to remove from the wort. The majority of hops used in the craft brewing industry are pellet hops.
  • 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. Their bulk also makes them more difficult to store and more susceptible to spoilage.
  • Extract – For hop extracts, the alpha acids and essential oils are pulled from the cones using heat and various solvents. These concentrated liquid extracts can be used in the brewing process just like hops. There are separate extracts for bittering, flavour and aroma. They are mostly used by large breweries, although they are sometimes used by smaller breweries and the home brewer. Hop extracts are easy to store and can be kept for long periods of time without spoilage.

Brewing Beer with Hops

Beer brewers use hops to impart bitterness, flavour and aroma. To achieve this brewers add hops at different stages during the brewing process. While most hops are added in the boil kettle they can be added a various stages prior to and after the boil as well to impart the desired characteristics of a beer style.

  • 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 flavour and aroma.
  • Bittering Hops – Bitterness from hops comes from alpha acids found in the lupulin glands of the hop flowers. In order to become bitter these acids must be chemically altered, isomerized, by boiling. 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.
  • Flavour Hops – Hop flavour and aroma are derived from essential oils found in the lupulin glands. The flavours are released as these oils become dissolved into the wort during the boil. Because these oils are highly volatile and are to a large degree lost to evaporation, flavour 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 evaporation.

Hops can be added at other points in the brewing process to enhance the flavour and aromatic qualities of beer. The most common of these with the home brewer is dry hopping. In this process hops are added to beer in the fermenter or racking tank. The hops are left in the beer for a period of time allowing the essential oils to dissolve. Dry hopping provides a very bright and fresh hop aroma with slight enhancement of flavour.

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