But does the color matter?

A bottle's color determines just how much light gets through to the beer inside.

Light may not seem like a big deal, but it can cause chemical reactions in beer that

affect the taste.

Brewers call these beers “lightstruck.”

Molecules from hops known as iso-alpha-acids are what make beer bitter, but they also make

beer vulnerable to light.

Visible light breaks apart these iso-alpha-acids with the help of riboflavin, also known as

vitamin B2, from barley malt.

One of the resulting molecules, known as an oxyl radical, loses oxygen and carbon atoms

and becomes a carbonyl radical.

That molecule is eager for a new partner to bond with, and it finds one in sulfhydryl

molecules that form when visible light breaks apart amino acids found in barley malt.

When they pair up, they form a new compound called 3-methyl-but-2-ene-1-thiol, which is

a bit of a mouthful, so it's often referred to as 3MBT.

3MBT happens to be very similar in structure and chemical makeup to the compounds responsible

for a skunk's distinctive odor, and we can taste it at just a few parts per billion.

Some brewers use specially treated hop extracts so iso-alpha-acids won't break apart and

form 3MBT.

But even these beers may not be safe from funky flavors.

Light can still cause a reaction that forms a molecule called 2-sulphanyl-3-methylbutanol,

which tastes like onion.

Different bottle colors block different amounts of light.

Unsurprisingly, clear bottles offer no protection from light, and green bottles aren't much

better.

But some brewers still use them and customers have come to expect skunky beer that might

require a slice of citrus.

Amber bottles are most common for a reason.

They block the most light, almost completely stopping skunking.

But if you want to avoid these pungent molecules, your best bet is to stick to sipping beer

from cans.

For Scientific American, I'm Kelsey Kennedy