Leftover Brewing Hops Tripled Sunscreen SPF In Lab Tests

Every year, craft breweries generate mountains of leftover hops, the green, cone-shaped flowers that give beer its bitter kick and hoppy aroma. Much of it is discarded after brewing. But a team of researchers in Brazil has discovered that this brewing waste appears capable of more than tripling a sunscreen’s measured SPF in lab tests.

Scientists from the University of São Paulo and the Federal University of Espírito Santo tested whether extracts made from used hops, leftovers from a brewing technique called dry-hopping, could improve how well sunscreen blocks ultraviolet rays. When the recycled hop extract was mixed into a sunscreen formula using water as the solvent, the product’s sun protection factor jumped from about 54 to 178. According to the researchers, this is the first successful demonstration that both fresh and brewery-recycled hop extracts can work as add-on ingredients in sunscreen formulas, evaluated using a standardized lab method.

Published in Photochem, the paper arrives as the cosmetics industry faces growing pressure to find natural, eco-friendly alternatives that are gentler on human skin and fragile ocean ecosystems.

Hops Already Have a History in Skin Research

Hops have long been valued for more than just beer. The plant contains biologically active compounds, including bitter acids and antioxidants, that earlier research has shown can protect against UV damage at the cellular level. That prior work made hops an intriguing candidate for skin care.

What sets this study apart is its focus on waste. During dry-hopping, hops are added after fermentation to intensify aroma and flavor, and an estimated 85% of the plant’s beneficial compounds remain trapped in the leftover material. Breweries typically discard it. Could those abandoned compounds still do useful work?

To find out, the team obtained two types of hop material: commercially purchased pellets that had never been used in brewing, and material that had already gone through dry-hopping and would normally be thrown away. Both were soaked overnight in ethanol, put through a second extraction step, dried, and stored.

A Compound Found Only in the Waste

Using a lab technique that separates and identifies chemical compounds, the researchers mapped what was in each extract. Both contained bitter acids typical of hops. But the reused extract held something unexpected: it was the only one that contained a compound related to xanthohumol, a plant pigment studied for its antioxidant and anti-inflammatory properties.

Xanthohumol makes up only 0.1 to 1.0% of dried female hop flowers by weight. During conventional brewing, heat can transform it into a different compound. Because dry-hopping happens after fermentation and cooling, the researchers suggest this may help preserve xanthohumol-related compounds in the leftover material. They also proposed that other compounds in the fresh extract may have masked the xanthohumol signal, and that the brewing process consumed those competing compounds, concentrating xanthohumol in the waste.

When the team ran a standard antioxidant test, the fresh hop extract showed moderate activity, while the reused extract showed none. The researchers noted this does not necessarily mean the reused extract lacks antioxidant potential. Previous research cited in the paper found that even pure xanthohumol performs poorly on this particular test, which may not capture how the compound actually works.

Reused Hops Dramatically Raised Lab SPF Scores

Eight sunscreen formulas were prepared, all containing the same standard UVA and UVB filters at identical concentrations. The formulas differed only in which hop extract they contained and which solvent was used: distilled water or one of three oily liquids. Each was spread onto specialized plastic plates and analyzed using an instrument measuring how much UV light passes through the sunscreen film.

Without any hop extract, the control sunscreen delivered an SPF of about 54. Formulas using oily solvents generally clustered between roughly 40 and 78. Water-based formulas stood out sharply. Fresh hop extract in water pushed SPF to about 117, while the reused hop extract in water reached approximately 178.

All formulas qualified as broad-spectrum sunscreens. However, the hop extracts did not meaningfully improve UVA protection. SPF mostly reflects defense against sunburn-linked UVB rays, while broad-spectrum sunscreens are designed to cover both. For now, the hop extract looks more like a helper ingredient than a replacement for standard UV filters.

From the Brewery Floor to the Lab Bench

Discovering that material destined for the garbage can improve a product’s performance fits what scientists call a “circular economy” approach: turning waste streams into value. The cosmetics industry has been moving toward plant-derived ingredients as consumers grow more environmentally conscious.

All testing was done on plastic plates in a lab, not on human skin, and the xanthohumol-related compound was only tentatively identified. Future studies would need to test formulas on actual people and account for variables like growing conditions and harvest year, which can affect chemical makeup.

A waste product breweries generate in large quantities, one that retains the vast majority of its beneficial compounds, significantly raised sunscreen SPF scores in the lab when prepared the right way. For an industry searching for greener ingredients, a promising candidate may have been sitting at the bottom of a fermentation tank all along.

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Disclaimer: This article is for general informational purposes only. Do not use hop extracts or homemade mixtures as sunscreen. Always use regulated, broad-spectrum sunscreen products as directed.

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