How does beer go skunky

The sunlight breaks down the alpha acids to produce sulfur compounds, specifically, 3-methylbutenethiol if you want to be nerdy about it.

The reaction also occurs very quickly: 30 seconds of exposure in clear glass bottles is more than enough time to get skunky. There are a couple different ways that brewers can combat skunking. Packaging in cans rather than bottles prevents skunking entirely as light cannot pass through. However, the majority of people prefer bottles to cans, as shown by the study Bottled vs.

Because of this, bottles are still heavily marketed and sold in the industry. Even dark brown bottles can, over time, let in too much light.

When this happens, the bitter, light-sensitive compounds in hops known as isohumulones break down and bind with the beer's sulfur compounds.

The result of this chemical reaction is a byproduct called 3-methylbutenethiol MBT , which is chemically similar to the stinky spray of an actual skunk.

It's so off-putting that tasters have been known to detect MBT in minute amounts -- as low as one-billionth of a gram in a ounce milliliter beer. Sometimes beer plagued by MBT is commonly called "light-struck" beer [source: Solis ]. However, some beers are brewed to taste skunky. Using particular strains of lager yeast and brewing conditions, some brewers are shooting for this distinctive, sulfur-infused result.

A German-style Pilsner is a good example of this. It's good to know the difference between a beer that's been skunked by accident and one that considers the pungency part of its flavor profile [source: Beer Advocate ].

And, for good measure, take a few precautions. If you are after a non-skunked beer, buy it in a keg or can. If you do prefer bottles, don't buy them from a brightly lit cooler or a sunlit display. And by all means, when you get the brew home, keep it out of sunlight [source: Harbison ].

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The skunky aroma in some beers is caused by a chemical reaction that occurs when ultraviolet light interacts with bitter hop compounds.