Why is my beer turning grey?

I have noticed recently that a couple of my beers were starting to look a little “grey”. I first noticed it with batch 36. This was bottled over 4 months ago. While the colour doesn’t look great, there aren’t any “off flavours” although the beer has lost come of it’s overall “hoppiness”.

Then I noticed that two very recent brews – batch 50 and batch 51 – were also showing signs of the same deterioration. And this time it was within a month of bottling!

It looks like there are two possible reasons for this:

• Oxidation. This can happen during fermentation or bottling. I have been cold crashing my beer recently and during this process the fermentation vat can build up negative pressure (pulling in air from outside) as the beer cools.
• Sunlight during secondary fermentation. Sunlight apparently can negatively affect the yeast. It is important that when bottle conditioning that the bottle are kept out of direct sunlight. I don’t know this! Some people are suggesting that even 20 mins in sunlight can do significant damage.

I think the culprit here is the exposure to sunlight. In hindsight, I haven’t been as consistent as I could have been in storing the bottles during secondary fermentation. The bottles are left in the warm for a week and then put them in the cellar for at least two weeks. It is the week in the warm that has done the damage. Recently, the crates of bottles have been left in the sun – often for the entire week! Particularly batches 50 and 51! Duh!

So we live and learn! And we have learnt the hard way here! Batches 50 and 51 were tipped down the drain! What was left of batch 36 went the same way and I am keeping an eye on the others too! Light, hoppy ales are apparently very prone to this.

So here are the changes that I have made to my process:

• Oxidation. I am now putting a little bit of pressure into my fermentation vats during the cold crashing. It is about 1PSI. But it is enough to stop any air from outside being sucked in. You will need to remove the airlock and replace it with something like this intended for doing pressure transfers. However, I don’t think oxidation was the problem here.
• Sunlight. Easily fixed by making sure that the bottles are conditioned in a warm and DARK location. They are then moved down to the cellar. Just wish I had been a bit more consistent with this over the last few months.