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Skunked Beer: What You Need to Know

Enjoying a beer in the sun is a summertime rite of passage. There’s only one thing that could ruin it…getting skunked! While being sprayed by a certain black and white striped animal would certainly not be ideal, we’re talking about when a bottle of beer is exposed to direct sunlight, resulting in a sulfur taste.

How It Happens

Skunked beer is bottled beer that undergoes a chemical reaction when exposed to ultraviolet or artificial light. To break down that reaction further, you’ll need to know the main ingredients used in making beer: hops, yeast, grain and water. Hops contain alpha acids, which are very sensitive to light. When these acids break down, they react with the sulfur content in the beer. This produces a compound known as 3-methyl-2-butene-1-thiol (MBT), which smells strikingly similar to a skunk’s secretion. 

What It Smells Like

Our taste buds are very perceptive to sulfur compounds, so it doesn’t actually take a lot of sunlight to completely ruin a beer. Skunked beer may smell like burnt rubber, a musty basement or wet cardboard. And even though it smells awful, it’s not unsafe to drink. The chemical reaction only affects the profile of the beer.

Why the Bottle Matters

Because light exposure is the main cause of skunked beer, UV rays can only reach beer through glass bottles. Aluminum cans effectively block out the light. 

You’ll notice most beer bottles are brown or green. That’s because those shades slow down the skunking. Brown bottles can block out light under 500nm in wavelength while green glass is only capable of blocking light that is under 400nm in wavelength. Clear bottles are least effective. But that doesn’t mean they will always be skunked. Brewers that opt for clear bottles likely use tetra-hops, which are a form of hop extract or inactive hops that are resistant to light.

How to Prevent It

Now we don’t have control over how a beer is packaged and handled by retailers, but we can make minor adjustments to avoid skunking:

  • Consider cans instead of bottles
  • If you buy bottles, make sure the display isn’t directly in the sunlight
  • Store it in a dark, cold place or the fridge as soon as possible
  • Use a cooler with a lid if you’re drinking outside