July 1, 2022

Hops by the Zentner


European countries, prior to the development of the metric system, used an interesting array of measures to quantify daily life. One of my favorites is the zentner. A zentner is an old unit of measurement used in Northern European countries from Germany through Scandinavia which was tied to agricultural products. A zentner is 100 units, where the base unit can vary widely, but was commonly associated with the old German pound, or pfund.

The one agricultural product most often associated with the zentner was hops. Since hops really only have two commercial uses, beer and decoration, the zentner is therefore most associated with beer. In case you’re wondering, a zentner of hops is 50 kilograms worth in modern day measure.

I mention the zentner for one simple reason; very few people know anything about hops, and yet without them, beer would not exist as we know it today. This month I take a look at the humble, yet noble hop, and its contribution to the world of beer.

Hops are the flower cones from hop vines. The flowers look somewhat like small green pinecones. The hop vine is a perennial climbing vine that often grows to heights around 15 feet. The above ground portion of the vine dies off each year and regrows from the dormant rootstock.

There are two distinct hop species, Humulus lupulus and Humulus japonicas. The japonicas species is strictly for decoration as it contains no resins and is therefore of no use to brewers. Hops are closely related botanically to the Cannabis family of hemp, marijuana, and hashish fame.

Hops tend to be susceptible to fungal diseases such as molds and mildews, as well as the hop fly aphid. Infections often require burning the plants to the ground with a total loss of crop, so hop growers tend to be a mercurial bunch suspicious of anyone visiting their hop vineyards.

Hops are predominately grown in Germany and the United States, with smaller but significant crops coming from Eastern Europe, Australia, New Zealand, and South Africa.

The primary purpose of hops in beer is to balance the sweet flavor of malt with the bitter character present in the a-acids of the hop’s resin fraction. Hops add aroma and flavor characters through essential oils, which are often described as herbaceous, citrusy, or spicy notes in the beer. Hops also act in a natural preservative fashion, extending the life of beer and preventing spoilage.

The bittering character of hops is the result of a-acids which are present in the resins of the lupulin glands near the base of the cone alongside the seeds. The acids are referred to as humulones, and there are three specific chemical compounds: humulone, cohumulone, and adhumulone.

The acids are extracted during the wort boil. Extraction is a slow process with limited capacity, so wort boils typically require an hour during the brewing process, with as little as 25% of the bittering potential captured in the extraction.

During the boil, the acids undergo an isomerization into the iso form that makes them much more soluble in beer. Each compound forms both a cis and trans version of the isomer during the conversion, giving a total of 6 distinct bittering acids that hops contribute to beer. The iso-a-acids are the light sensitive compounds in beer that give the skunky, light struck character if improperly stored.

The essential oils of hops are extracted much more easily and are quite volatile; as a result hop varieties with desirable aroma characters are typically added near the end of the boil as finishing hops, or afterwards in aging by the process of dry-hopping.

Hops oils are very complex, containing at least 300 aromatic compounds. There are no analysis methods available to determine the ideal mix of hop oils, so the process is very much the art in the hands of the brewer.

Hops are commercially available in whole cones, pellets, or as extracts. The pellet form is most commonly used in commercial brewing, with the whole cone option being less common at least by the number of brewers. The extract version is used by several large commercial brewers, particularly as it maximizes bittering potential, and has been rendered light stable.

The hop has contributed to beer for centuries. The beer that people love would simply not be the same without it. The rise of the craft beer industry in particular celebrates hop’s role in beer. So grab a hoppy beer and celebrate the contribution of this little flower to the beverage world.

Drink responsibly.

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