Stop by the beer aisle at your local grocery store and you’ll find dozens, if not hundreds, of brands, styles, and flavors of beer to choose from. The selection can range from classic American lagers to stouts to more adventurous choices like imperial India pale ales. Despite the diversity, nearly all beers share the same four basic ingredients. Water, yeast, and malted barley all have an important role to play—but none shapes the flavor and character of the finished product quite like hops.

What is a hop?

The common hop (Humulus lupulus) is an herbaceous perennial vine native to Europe, southwestern Asia, and North America. The vines can reach anywhere from 10 to 30 feet in height, and are often grown on a support structure such as a trellis.

Hops are dioecious, meaning there are separate male and female plants. Only the flower clusters of the female plant are used to flavor beer. Those cone-shaped flower clusters, known botanically as strobiles, mature in late summer.

Humulus lupulus is from the same family as another famous plant — Cannabis sativa (marijuana). The two botanical cousins are members of the Cannabaceae family, along with members of the Celtis (hackberry) genus.

How hops affect beer

Alpha acids from hops add a bitterness to beer that helps balance out the sweetness of the malted barley. That bitterness is measured in International Bittering Units, or IBUs. The higher the IBU, the more bitter the beer. A typical American lager has an IBU around 10, while a hop-heavy India pale ale may have an IBU in the 50-90 range.

Hops can also be used to add aroma at the end of the brewing process. Different varieties of hops can impart vastly different flavors and aromas—such as piney, floral, or fruity. Commonly used American cultivars include ‘Cascade’, ‘Chinook’, ‘Amarillo’, and ‘Centennial’.

Collection Connection

Hops are represented in different ways across several of our collections at the Missouri Botanical Garden.

Living Collection – You’ll find several hop vines growing around the Garden, but the plant is featured most prominently in the St. Louis Herb Society Herb Garden. The ‘Aureus’ or Golden variety grown here is used more for its ornamental value than for brewing beer. Hops were named the Herb of the Year 2018 by the International Herb Association.

Herbarium Collection – The Garden’s herbarium is home to several specimens of Humulus lupulus, including the wild North American varieties pubescens, lupuloides, and neomexicana. These vouchers can be used by researchers to help identify plants or track other data such as geographic location. One specimen was collected in Maine back in 1893.

An herbarium voucher for Humulus lupulus var. pubescens. This specimen was collected in the woods near Kansas City in 1992.

An herbarium voucher for Humulus lupulus var. lupuloides. This specimen was collected in Maine in 1893.

Biocultural Collection – Our biocultural collection, curated by the Garden’s William L. Brown Center, focuses on the connection between plants and people (the study of which is known as ethnobotany).  Hops in our biocultural collection include a soap made with hops, and several packages of compressed hops from an herbal store in San Francisco.

Soap made from Hops and other botanical ingredients. Purchased by ethnobotanist Eric Feltz in the Ozark region of Missouri. Label reads, “HopHead Shampoo, Shampoo and Conditioner, Lather in hands, apply through hair and rinse, packaged with recycled grain bag, Ingredients: Schlafly APA Dry Hopped Beer, Coconut, Olive, Wheat Germ, Castor Oils, Sodium Hydroxide & Fragrance. All About Green.

A package of compressed hops from the Garden’s biocultural collection.

Rare Book Collection – Hops have been used in brewing for about 500 years, but have long been regarded for other medicinal properties. Several books in the Garden’s Peter H. Raven Library rare book collection feature hand-drawn images of hops along with a description of the plant and it’s various uses. In the 19th century, for instance, hops were often used as a digestive aid and a mild sedative.

“In medical practice the hop has been found a decided and useful tonic. A fermented decoction, known by the name of hop beer, and usually formed from this article with the simple addition of treacle, is much used in the New England states. When made sufficiently bitter with hops, and taken as a common drink at meals, it promotes digestion more than any of the table liquors in common use.”

Excerpt from American Medical botany, volume 3 (1820)

This image of Humulus lupulus appears in American medical botany, by Jacob Bigelow (1820).

This image of Humulus lupulus appears in American medicinal plants, by Charles Frederick Millspaugh (1887). The digitized image is from the NC State Library, but Garden has several copies in its general collection.

This image of Humulus lupulus appears in Köhler’s Medicinal Plants, a German herbal published around the turn of the 19th century.

If you’re a learn-by-doing sort of person, or just a fan of good beer, the Garden has you covered on that front as well. Fest-of-Ale is an annual event bringing together some of the region’s best microbreweries at the Garden, organized by the Young Friends’ Council in support of designated projects on the Garden grounds. Many of these vendors can be found at other Garden events throughout the year.

Cassidy Moody – Digital Media Specialist

Learn more about the botany behind some of your favorite beverages: 
Grapes in the Garden: The Science, Production, and Appreciation of Wine
Collection Connection: Whiskey and Research