What Is the Use of Hop Extract for Brewing?

Hops, scientifically known as Humulus lupulus L., also called snake grass, Tuo De Hua (the name in the Compendium of Materia Medica), Tang Cao Hua (Japanese), and Hu Bu (a phonetic translation of the English name “hop”), are perennial, climbing, herbaceous plants with fibrous roots belonging to the Cannabaceae family and the Humulus genus [1–2]. Its primary growing regions are concentrated between latitudes 35° and 55° north and south [3–4], with major production areas distributed in Germany, the United States, the United Kingdom, New Zealand, Czechoslovakia, Australia, and China, among others. In botanical classification, the Cannabaceae family was branched off from the Moraceae family; therefore, some literature still records it under the Moraceae family.

Although the Chinese names “Humulus” and “Cannabis” are used to refer to the same genus, their scientific name is Humulus, so there is no ambiguity. Hops have been used in beer brewing since the 12th century, and to this day, their primary use remains in beer production. Due to their ability to impart a distinctive bitterness and unique flavor to beer, as well as their antimicrobial properties, they are often referred to as the “soul of beer” [5]. Due to its excellent antibacterial properties, hops were initially added to beer brewing primarily to extend its shelf life. Additionally, beyond beer brewing, hops have numerous other applications. This paper provides an overview of the antibacterial properties of hops and their expanded applications.

1 Antibacterial Properties of Hops

The chemical components in hops, including humulone, lupulone, xanthohumol, and other flavonoids, inhibit the growth of Mycobacterium tuberculosis, Staphylococcus aureus, Bacillus subtilis, and other bacteria. Due to the strong lipophilic nature of humulone, it has a high distribution coefficient, easily penetrates the wax layer of Mycobacterium tuberculosis, and exerts a special affinity, thereby inhibiting the growth of Mycobacterium tuberculosis. Its inhibitory effect is stronger than that of lupulin [6–8]. It has been formulated into hop extract tablets, hop extract emulsions, and hop extract extracts for use. Table 1 lists the main antibacterial components in hops and their effects.

Extensive research has shown that hop components have excellent inhibitory effects on most Gram-positive bacteria but are almost inactive against Gram-negative bacteria and yeast, and even have a certain proliferative effect on yeast.

2 Applications of hop extracts

2.1 Medicinal uses of hop extracts

Like rosemary and Jerusalem artichoke, hops have been used as herbal medicine since the 13th century. The “Tuo De Hua” mentioned in the Song Dynasty's “Kaibao Bencao,” cited in “Bencao Gangmu,” refers to hops [19], which are described as having a bitter and slightly cool nature, with functions including stomach-strengthening, calming the mind, resolving phlegm and coughing, and anti-tuberculosis activity. The *Food Herbs and Folk Remedies* also records [20] that hops have inhibitory effects on various bacteria and exhibit sedative and estrogen-like activities. In folk medicine, hops are commonly used to make tea, with functions including stomach-strengthening, vision-improving, thirst-quenching, blood pressure-lowering, cough-relieving, diuretic, and sedative effects. The medicinal part is the green flower spike. Modern pharmacology has conducted more in-depth research on the anti-inflammatory, antitumor, antioxidant, antiviral, hypoglycemic, digestive, estrogenic, and sedative effects of hops. The medicinal properties of hops are summarized in Table 2.

2.2 Application of hop extracts in food processing

Hops extracts are used in the bread industry as additives to preserve yeast and manufacture bread, imparting preservative, prolonged shelf life, and fermentation-promoting properties to bread [51]. Dong Haizhou et al. used a combination of yeast strains selected through repeated screening, including aromatic yeast, along with wine yeast, hops fermentation mash, lactic acid bacteria, and appropriate chemical leavening agents, to conduct a systematic study on the improvement of steamed bun flavor. Through natural fermentation, steamed buns with a sweet and fragrant flavor were produced, significantly improving the texture of the steamed buns. This has certain guiding significance for promoting the industrialized production of steamed buns in China [52]. Additionally, hop β-acids have shown excellent efficacy in the storage of concentrated orange juice [53]. When added at a concentration of 3 mg/kg to 60% DS concentrated juice, hop β-acids effectively inhibited microbial activity in the juice and significantly prolonged the formation time of converted sugars and acids compared to a control sample.

2.3 Applications of Hop Extracts in the Sugar Industry

The application of hop β-acids in the sugar industry significantly increases sugar yield [54–56]. In 1994, hop products were successfully applied for the first time in the beet extraction process, where their antibacterial activity controlled microbial growth-induced sugar loss and the formation of dextroses. This represents a new application area compared to the traditional use of hops in the brewing industry. Over the past decade, β-acids from hops have been used as a natural antimicrobial agent in the sugar industry to control the growth of thermophilic bacteria or other Gram-positive microorganisms. During beet processing, fermentation often occurs in extraction towers, producing lactic acid. The β-acids in hops have demonstrated excellent efficacy in inhibiting the formation of NO₂ and preventing anaerobic bacterial infections in extraction towers. This compound exhibits highly effective antimicrobial activity, with higher activity at lower concentrations, particularly against Clostridium species (minimum inhibitory concentration of 1 μg/mL).

 These natural products are harmless to humans and can be biodegraded in the external environment. The alkaline solution of hop β-acids, branded as “BetaStab,” has been used in the sugar industry [57].

2.4 Application of Hop Extracts in Brewing

In brewing, the significant antibacterial activity of hop extracts can inhibit the adverse factors caused by the proliferation of contaminants during production, thereby reducing yield losses. Antibiotics are commonly used in the brewing industry to control bacterial growth; however, they also adversely affect yeast activity and performance. The components of hops can enhance yeast activity and have a slow flocculation effect, resulting in conditions more favorable for yeast growth and faster fermentation. During yeast washing, the components of hops produce a synergistic antibacterial effect at low pH, and this effect has been proven effective in ethanol production plants and distilleries in the United States [58].

3 Outlook

With the deepening of research on hop extracts and the growing focus on natural plant-derived antimicrobial agents and plant bioactive components, based on their unique antibacterial functions, hops have been developed into various products such as shampoos, hair dyes, or as a key ingredient in hair growth formulas in many countries and regions. Additionally, many regions have included hops and their extracts in the category of food supplements, and some have developed them into health pillows with insomnia-relieving properties. Although hops are currently primarily used in the beer brewing industry in China, it is believed that with increasing attention, the development and utilization of hops will undoubtedly thrive in the near future.

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