Off-flavour #2: Lightstruck

The “Off-flavours” series covers the three most common ways the flavour of beer can be ruined after it leaves the brewery and what can be done to prevent this from happening. New to the series? Start here.

Beer is a fascinating, diverse and delicious beverage, but if it’s not properly stored, it can develop some not-so-delicious off-flavours. (As a note, none of these off-flavours are health risks, but they certainly are unpleasant!) 

Next up in this series, let’s explore what happens to beer when it’s exposed to light, aka it’s lightstruck or skunked.

What are the signs of a lightstruck beer?

A lightstruck beer will give off a skunk-like aroma.

(If you’re not familiar with the smell of a skunk, this aroma is also described as smelling like freshly brewed coffee, grass, or marijuana.)

What causes lightstrike?

As the name suggests, lightstrike is caused by beer’s exposure to light – including sunlight, fluorescent light, and most LED lights.

It’s formed by a reaction between certain wavelengths of light (both blue and UV) and hop’s bittering compounds (the iso-alpha acids) and may be evident after just a couple of minutes of light exposure.

How do we prevent lightstrike?

Cans, kegs, and bottles in closed case boxes that completely shield beer from light give maximum protection from lightstrike or skunking.

But, outside of their boxes, bottled beers are subject to skunking:

• Brown glass blocks most of the wavelengths of light that cause skunking, and therefore offers superior protection to clear and green glass
• Green glass blocks very little of the light that causes skunking
• Clear glass offers no protection against skunking

There is a way for brewers who package their beers into clear or green glass bottles to avoid the development of this off-flavour, and that is by using specially modified hop extracts that do not react with light. This is what Miller uses in its Miller Lite product, for example, so even though it’s in a clear glass bottle, you will not detect lightstrike.

But other brewers that use clear or green glass bottles as a marketing choice have come to accept this aroma as part of their beer’s character. Consumers are very tolerant of this aroma, but technically it’s still considered an off-flavour.

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Time to close out the “Off-flavours” series with off-flavour #3: draught line infection.

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