Why does my beer smell like rotten eggs?

Who likes the smell of rotten eggs in their beer?

No one.

There was a time last year when I went to bottle my beer.

I'd just sterilized the bottles within an inch of their lives and I was ready to get the precious amber fluid into them.

And with that first pour from the fermenter into the green glass bottle, I got the most rank smell.

Rank.

Smell.

Of.

Rotten Eggs.

It was like I had cracked open a rotten egg and fanned it up my nose!

It was disgusting like some kind of vile hydrogen sulfide bomb had been let off and the aroma was trying to burn my nostrils.

My brew was contaminated and I was gutted

There could have been a couple of reasons why the rotten eggy smell was happening. That rotten egg smell can usually be identified as the gas hydrogen sulfide.

It's probably the most obvious symptom that your beer has become contaminated.

It is the bi-product of the yeast strain or bacteria that have snuck into your brew (did we ever mention you've got to sanitize your equipment?).

The thing about lagers and rotten smells

All is not necessarily lost, however.

You can fix this problem if the sulfide was produced by the yeast and not bad bacteria.

Lager yeast strains are quite prone to producing sulfide odours.

This is normal.

If you properly condition your bottled beer (the lagering process) by letting it stand for a few weeks, the smell should go away before it's time to drink.

This why we also recommend that new brewers try an ale or two first to avoid this problem and being disappointed with their foray into brewing. 

The news is not so good if you have a bacterial infection 

When is such news ever good?

In my case, I think it was clear that the beer was infected. The smell was pungent and a wee taste test suggested worse things were on offer.

But even though I was pretty sour, I was a stubborn bugger and bottled anyway on the off chance a bit of time conditioning would let everything sort itself out.

How wrong was I?!

The beer I tasted after two weeks was probably the worst thing I have ever put in my mouth and I once lost a beer drinking game involving a rinsed out kitchen cloth...

I reckon this bad beer would have made me sick if I had of drank a whole glass.

The rest of the brews were opened and tipped out. What was very interesting was there was a massive amount of CO2 / bubbles foam released when each cap was removed. They were giant gushers!  I imagine this was due to the unwanted bacteria continuing to work its own fermenting magic on the malt.

Either way, the lesson here as always is to do your absolute best to ensure that you have clean equipment and that you've done your best to sanitize it, and kept it clean during the beer brewing process.

If you find your beer in this condition before bottling, I'm afraid all you can do is dump the batch.

And then clean the heck of your fermenter and bottles!

This was a brewing lesson I will never forget. I'll be lax in some areas but will always make sure my equipment is clean and sanitized!

Skunked beer

While we're here talking about ruined beer, let's talk about skunked beer. This is when a chemical reaction happens in the bottled beer due to exposure to sunlight.

So named after the smell a skunk can release, lightstruck beer is caused by the UV radiation in light from the sun and retailer's lights. The so-alpha acids in the beer (which come from hops) are broken down and form a new compound in the beer by joining with any proteins floating around.

This compound stinks!

Brown glass is pretty handy at preventing this from occurring but not so much green bottles or clear glass. So, the trick to avoiding skunked beer is clearly to store your beer in the dark.

In summary:

• If you are brewing a lager, the smell could be 'normal' and may disappear after the beer has been conditioned
• It could well be your beer is contaminated by bacteria, in which case nothing will save it. Head to the pub for a self-pitying pint.
• Lightstruck or skunked beer can happen when the bottled beer is left in sunlight too long.
• Let your beer condition properly so that the yeast has time to work it's magic properly.