Oxidation during fermentation

I have a small mini fridge I use for fermenting lagers that I keep outside. Yesterday I realized that the door seal had a 1/2" gap at the top which would let some amount of sunlight into the fridge for several hours per day. At what point is sunlight an issue? For this particular batch I had pitched about 18 hours before I noticed the sunlight issue and fermentation activity was really just beginning, however the reason I checked in the first place is a lager I just put on tap definitely has an oxidized taste to it, so I'm guessing that several weeks of exposure during and after fermentation definitely had an effect in my case. Any guesses?

Oxidation has nothing to do with light. Light will react with the iso-alpha acids to create "skunked" flavors. Oxygen will create cardboard or sherry flavors.

That small amount of light shouldn't be a problem. What flavors are you getting exactly?

I can't describe the off flavors well enough here. It doesn't taste like wet cardboard or sherry, there's almost a bad residual taste of some sort on the tongue after taking a sip. I have made many lagers and usually do not have this aftertaste. I do 90 minute boils when using mostly pilsner malts, and control my temps well.

What off flavors would be associated with sunlight?

sdbrew1024 said:

What off flavors would be associated with sunlight?

Click to expand...

Skunky is a pretty good description, put a bottle of Heineken in a window for a week and then taste it.

Another good description for those you know the scent... smells a little like weed, good weed. Although I forget what that smells like now .

sdbrew1024 said:

I can't describe the off flavors well enough here. It doesn't taste like wet cardboard or sherry, there's almost a bad residual taste of some sort on the tongue after taking a sip. I have made many lagers and usually do not have this aftertaste. I do 90 minute boils when using mostly pilsner malts, and control my temps well.

What off flavors would be associated with sunlight?

Click to expand...

Shooting in the dark here, but is it a kind of slick feeling on the back of your tongue. Maybe a slight hint of butter or buttered popcorn? I ask becasue that particular taste I described is Diacetyl. If you didn't do a proper diacetyl rest with a lager, this might be the case. I've tasted a beer doctored with Diacetyl, so I know for a fact that I cannot taste or smell it (some people can't). For me, it was alwasy this off taste/slickness. I'm not 100% sure thats the problem. Maybe try getting someone you know is really sensitive to diacetyl to taste it?

That could definitely be it. My notes on this brew are fairly incomplete for some reason, but the notes do not list a diacetyl rest... Interesting flavor, I don't think I have ever tasted diacetyl before