The hop cones of the female plant of the common hop species Humulus lupulus L. are grown almost exclusively for the brewing industry. Only the cones of the female plants are able to secrete the fine yellow resinous powder (i.e. lupulin glands). It is in these lupulin glands that the main brewing principles of hops, the resins and essential oils, are synthesized and accumulated. Hops are of interest to the brewer since they impart the typical bitter taste and aroma to beer and are responsible for the perceived hop character. In addition to the comfortable bitterness and the refreshing hoppy aroma delivered by hops, the hop acids also contribute to the overall microbial stability of beer. Another benefit of the hop resins is that they help enhance and stabilize beer foam and promote foam lacing. In an attempt to understand these contributions, the very complex nature of the chemical composition of hops is reviewed. First, a general overview of the hop chemistry and nomenclature is presented. Then, the different hop resins found in the lupulin glands of the hop cones are discussed in detail. The major hop bitter acids (α-and β-acids) and the latest findings on the absolute configuration of the cis and trans iso-α-acids are discussed. Special attention is given to the hard resins; the known δ-resin is reviewed and the ε-resin is introduced. Recent data on the bittering potential and the antimicrobial properties of both hard resin fractions are disclosed. Attention is also given to the numerous essential oil constituents as well as their contributions to beer aroma. In addition to the aroma contribution of the well-known essential oil compounds, a number of recently identified sulfur compounds and their impact on beer aroma are reviewed. The hop polyphenols and their potential health benefits are also addressed. Subsequently, the importance of hops in brewing is examined and the contributions of hops to beer quality are explained. Finally, the beer and hop market of the last century, as well as the new trends in brewing, are discussed in detail. Hop research is an ever growing field of central importance to the brewing industry, even in areas that are not traditionally associated with hops and brewing. This article attempts to give a general overview of the different areas of hop research while assessing the latest advances in hop science and their impact on brewing.

Although hop technology has been a substantial part of brewing science for the last 130 years, we are still far from claiming to know everything about hops. As hops are considered primarily as a flavour ingredient for beer, with the added benefit of having anti‐microbial effects, hop research is focused on hops as a bittering agent, as an aroma contributor and as a preservative. Newer fields in hop research are directed toward the relevance of hops in flavour stability, brewing process utilisation, the technological benefits of hops in brewing as well as hops as a source of various substances with many health benefits. However the more we find out about the so‐called “spirit of beer” the more questions emerge that demand answers. While hop research was only an ancillary research field for decades, during the last ten years more universities and breweries have determined that hops must play a meaningful role in their research efforts. This article gives an overview of the up‐to‐date knowledge on hop aroma, hop derived bitterness, and the role of hops in flavour stability as well as light stability. Hop research is a wide field, therefore in this review only selected topics are reviewed. Other research areas such as hops utilisation, the antifoam potential of hops, or the advances in knowledge pertaining to the physiological valuable substances of hops go beyond the scope of this article.

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Pentose-hexose monoterpene alcohol glycosides were isolated and semiquantitatively measured in dried Humulus lupulus cones using UHPLC-qTOF-MS/MS and HPLC fractionation followed by GC−MS. The samples evaluated included hop cones from five important dual-purpose cultivars (varieties) in the United States, from two locations (farms) per variety and from three distinct harvest time points (maturities) per location, as dictated by dry-matter (% w/w) at the time of harvest. Hop variety accounted for the biggest variation among the concentrations of pentose-hexose monoterpene alcohol glycosides as well as other volatile and nonvolatile chemical factors measured in the samples. This indicates that genetics plays a major role in hop flavor production. Interestingly, "maturity", or ripeness at the time of harvest, was the next most significant factor impacting the concentrations of pentose-hexose monoterpene alcohol glycosides along with most of the other volatile and nonvolatile factors (such as total oil concentration and composition). However, maturity notably had a bigger impact on some cultivars such as Sabro, Mosaic, Simcoe, and Citra. Surprisingly, farm (i.e., location, farming practices, etc.) accounted for the least amount of variation among the concentrations of the different analytical factors. These results highlight the importance of breeding/genetics as well as considering hop maturity/ripeness at the time of harvest on the production and subsequent development of analytical chemical factors associated with driving hoppy beer flavor. It is essential for future studies assessing the impact of different farming practices and locations (i.e., regionality, terroir, etc.) on the constituents in hops important for hoppy beer flavor to consider and account for the impact of hop maturity as well as genetics.

Non-alcoholic fatty liver disease (NAFLD) is considered to be the hepatic manifestation of the metabolic syndrome. Iso-alpha acids (IAAs), hop-derived bitter compounds in beer, have been shown to beneficially affect different components of the metabolic syndrome such as insulin resistance and dyslipidemia. However, IAAs have not yet been studied in the context of chronic liver disease. Here we analyzed the effect of IAA on the pathogenesis of NAFLD. Once, we applied IAA to mice in combination with a NAFLD-inducing Western-type diet (WTD), and observed that IAA significantly inhibited WTD-induced body weight gain, glucose intolerance, and hepatic steatosis. Fitting to this, IAA dose-dependently inhibited cellular lipid accumulation in primary human hepatocytes (PHH) in vitro. Reduced expression of PPAR-gamma and key enzymes of lipid synthesis as well as increased expression of PPAR-alpha, indicative for increased lipid combustion, were identified as underlying mechanisms of reduced hepatocellular steatosis in vitro and in vivo. Analysis of hepatic HMOX1 expression indicated reduced oxidative stress in IAA-treated mice, which was paralleled by reduced activation of the JNK pathway and pro-inflammatory gene expression and immune cell infiltration. Furthermore, IAA reduced hepatic stellate cell (HSC) activation and pro-fibrogenic gene expression. Similarly, IAA also dose-dependently reduced oxidative stress and JNK activation in steatotic PHH, inhibited HSC activation, and reduced proliferation and pro-fibrogenic gene expression in already activated HSC in vitro. In conclusion, IAAs inhibit different pathophysiological steps of disease progression in NAFLD. Together with previous studies, which demonstrated the safety of even long-term application of IAA in humans, our data suggest IAA as promising therapeutic agent for the prevention and treatment of (non)alcoholic (fatty) liver disease.