Beer bottles are typically just three colors.
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