Skunky beer odor

Northern Brewer General
1

Recently purchased a 6 of Henry Weinharts IPA, I like to sample so I thought what the hay? Pouring a glass, this stuff was nasty, and had a skunk odor to it. I have read that this is from light exposure so my question is: 1. How can such a large brewery have this problem? 2. For my Prof’s (Master Brewers) (I’m the 60 year old student) Can you clarify what causes this and how we as home brewers can steer clear of this.

THANKS!!

2

Assuming these were bottles and not cans, etc - Skunky commercial beer is probably due to how the beer was treated after it was packaged. Exposure to UV rays via sunlight would be the first suspect…

http://www.professorbeer.com/articles/skunked_beer.html
3

Yep. Once it leaves the brewery, they have no control over how the distributor handles it, the store handles it, etc. It was probably mishandled after it left the brewery. This is why you never trust a beer in a clear bottle. I have been on a Mexican beach where a guy has a metal tub filled with Corona & ice out in the direct sun… no thank you. As homebrewers, we can make sure our beer stays out of direct sun (or mechanical) light. Keep it cool and dark. If you keg, no worries. If you bottle, dark brown is best. As for the scientific reason, I can’t remember but there is a wavelength/spectrum thing that eggheads… er … science enthusiasts explain that goes over my head. I’m sure someone will be along any moment to explain it. Cheers.

4

If i’m not mistaken, its actually the hops being exposed to UV that gives off the skunky smell. isohumulones. Always store beer in dark bottles or kegs and keep bottles out of direct sunlight.

5

Not really able to help with your question but I did also try that beer and was not real impressed.

I dont recall if it was “skunky” but do recall that I was quite disappointed with the beer and would not buy that again.

6

One of our club members put this together. It gives a good explanation without your eyes glazing over.

Mercaptan/ Skunky Beer

        Definition: The compound produced is MBT(3-Methyl-2-butene-1-thiol), which is very similar to the chemical butylmercaptan or skunk spray. Volatile mercaptans are normal components of beer,contributing to aroma, and they increase on exposure to light.

        Characteristics: MBT is notappropriate in any beer, but some beers, notably Heineken and Corona arepackaged in light green or clear bottles, making the production of MBT and theoff flavors inevitable. Most people now consider the off flavors as part of thestyle. The off flavor is often referred to as light-struck like a skunk orfreshly-brewed coffee. 

        Causes:  When natural or artificial light is allowed topenetrate the beer container and initiate what is referred to as photolysis.This photolysis reaction breaks down the natural bitter alpha acid hopconstituents in the beer, leading to the formation of the compound MBT/SkunkyBeer. Increased risk with clear or green bottles, sunlight on brown bottles orgreen bottles (Can take as little as 15min in direct sunlight for a Eurolagerto develop detectable MBT)

         Management:: Fermentershielded from light; brown or opaque bottles opaque to 400-520 nm lightwavelengths; isomerized hop extract; storing beer in a cool, dark place.