Xanthohumol, a prenylated flavonoid (a type of polyphenol), found in the hard resin fraction of hops. It is somewhat unique, because nearly all other poly- and monophenols are found in nonlupulin plant material in the hop cone. Hop resins are divided between soft resins—those that are soluble in hexane—and hard resins—those that are soluble in ether. The soft resin fraction contains the hop’s alpha and beta acids, whereas the hard resin fraction contains the hop’s oxidized alpha and beta acids, as well as xanthohumol and its isomerized counterpart isoxanthohumol. Xanthohumol is the most abundant prenyl flavonoid in hops and may amount to nearly 1% of the hop-cone dry weight, depending on variety. Xanthohumol has no brewing value, because it does not contribute to or modify beer flavor. However, it does offer potentially very significant human health benefits. It has been identified as having strong anti-inflammatory, antioxidative, and broad-spectrum anticarcinogenic properties. It inhibits the metabolic activation of procarcinogens, it induces carcinogen-detoxifying enzymes, and it inhibits tumor growth at an early stage. In particular, it has been shown to be chemopreventive against breast and prostate cancer. Within the class of plant-based polyphenols, both xanthohumol and isoxanthohumol have high antioxidant properties, higher than genistein (which is found in soy) but not as high as quercetin (which is found in onions and fruit). Despite the high levels of xanthohumol in some hops, its presence in beer is very low because it isomerizes rapidly during kettle boil. Traditionally hopped lager beer may have between 0 and 30 parts per billion (ppb) xanthohumol, whereas more heavily hopped ales and porters can have as much as 100 to 700 ppb. The low concentrations in beer combined with its very low bioavailability means that the amount of xanthohumol obtained by drinking beer is negligible. Isoxanthohumol, on the other hand, is found at up to 100 times higher levels in beer. Heavily hopped beers may have between 800 and 3,500 ppb (or 0.8 and 3.5 ppm) isoxanthohumol. There is some evidence that intestinal microbiota can isomerize isoxanthohumol back to xanthohumol during the digestion process. If true, this may bring new attention to the possible health benefits of xanthohumol. See lupulin.