Fermentation - Out of direct light, why?

[TempTest]

Hello,

I am currently investigating some possible fermentation solutions for my small scale brews. In the past I have always covered the fermenter with a bin liner as I remember reading the fermenting beer should be kept out of direct light. I cannot relocate the source of this information. Can anybody tell me what the reason for this might be? Must I continue to do this? Is UV light the (only) issue? If so, if I were to (for arguments sake) put the fermenter within something transparent but with UV protection (so that I can still see the fermentation!) would this be acceptable?

Thanks!

[Jim]

The reason for keeping beer out of sunlight is because of a problem known as 'skunking'. This is a process where the UV in the light breaks down the hop oils and produces a horrible skunk like smell and flavour. The beer is also sometimes referred to as 'light struck'.

Some hop oils used in kits are immune to it apparently, but anything made from fresh hops needs watching.

[TempTest]

The reason for keeping beer out of sunlight is because of a problem known as 'skunking'. This is a process where the UV in the light breaks down the hop oils and produces a horrible skunk like smell and flavour. The beer is also sometimes referred to as 'light struck'.

Some hop oils used in kits are immune to it apparently, but anything made from fresh hops needs watching.

Hi Jim,

I am aware of skunking and appreciate this care is required for a packaged beer however is the same process also possible during fermentation? If so, is this problem caused *only* by light in the UV spectrum or the visible spectrum too? If the former then I should be fine simply storing the (transparent) fermenter inside a UV protected chamber. (Or indeed, affixing a UV protection film around the fermenter).

Thank you.

[Jim]

Hi Jim,

I am aware of skunking and appreciate this care is required for a packaged beer however is the same process also possible during fermentation? If so, is this problem caused *only* by light in the UV spectrum or the visible spectrum too? If the former then I should be fine simply storing the (transparent) fermenter inside a UV protected chamber. (Or indeed, affixing a UV protection film around the fermenter).

Thank you.

UV can affect the beer at any time. As long as your fermenter isn't in the sunlight you should be OK - many brewers use a fermentation fridge and this obviously keeps light away from it very effectively as well as controlling the temperature.

I'm not 100% sure if other components in the light can cause a problem - probably not as UV is the highest energy component of normal sunlight. Easily stopped though - I doubt if it would get through a normal translucent plastic fermenter for example (though I might be corrected on that one).

The main problem is with clear glass bottles.

[TempTest]

many brewers use a fermentation fridge

This is actually where my question first began - I'm trying to find an ideal small fermentation fridge for the limited space I have but most at this size are not suitable because of the space lost to to the door mouldings. The solution it seems is to get a glass door fridge (no door mouldings!) which has the added advantage I can see inside... The disadvantage light can too! However I'm hoping by applying some UV film you can buy it should resolve the issue allowing me the best of both. Any potential issues?

Thanks!

[Matt12398]

A far simpler solution is to cut or remove door mouldings.

[Capped]

It exasperates the missus no end when I close the kitchen window and door blinds when brewing/bottling operations and proceed in semi-darkness. Dunno how much the light affects beer but such a set up suits me as I'm a creature of the night and dislike light anyway. Win win!

[AnthonyUK]

According to this article there are two causes which are by both UV and visible light.

https://beersensoryscience.wordpress.co ... ghtstruck/

[TempTest]

That article suggests:

Visible light spectrum ~350-500nm
UV >380nm
Brown glass block >500nm
Green glass block >400nm

Assuming wikipedia is accurate visible is actually 400-700nm and UV is 10-400nm. Therefore, if the UV films actually do manage to block all the way up to 400nm then they'll protect as well as green glass bottles. Not ideal.

I guess if I go with a glass-door fridge I'll still need to either cover the glass up or cover the fermenter up (while in the meantime get a better idea of how effective the UV films are). All of these are more ideal than getting a solid door fridge as I trust myself to apply film more than I see hack at fridge mouldings!

Thanks!

[TempTest]

This is also a good article, focus on wines but interesting none-the-less:

http://www.winewisdom.com/articles/tech ... uck-wines/

"Stepp explained why M&S had not pursued this option. “A UV protective coating can be applied once the bottle is finished.. The coating has to be completely transparent on clear glass, otherwise it defeats the purpose. But if the coating is 100% clear, its protection only goes to 400nm. So the 440nm peak was not covered. And to get protection over 400nm, the protective coating becomes coloured.”"

So really UV coating removes a lot of the damaging spectrum but still leaves damage to occur in the visible spectrum. At which you either cover up or tint further...

[AnthonyUK]

TI guess if I go with a glass-door fridge I'll still need to either cover the glass up or cover the fermenter up (while in the meantime get a better idea of how effective the UV films are). All of these are more ideal than getting a solid door fridge as I trust myself to apply film more than I see hack at fridge mouldings!

Thanks!

Is the fridge likely to be in direct sunlight though?
Normal glass blocks around 40% of UVA and 97% of the shorter wavelength UVB so as long as it is shaded the risks are minimal.
Some polystyrene sheet over the glass is not a bad idea though as these display fridges tend to be less efficient than regular ones.

[TempTest]

The fridge I'm looking at already has UV protection on the glass door panel but I'm not sure if that helps any with the visible spectrum? The fridge will be located in a kitchen at worktop height, opposite a window *but* that room rarely gets direct sunlight because of some fencing less than a meter outside of the window. Do you think a glass-front fridge with UV protection treatment will be fine in itself or do you think I'll still need something additional?

I think the actual cooling performance should be acceptable - It's only damage from light I'm concerned with here.

[ManseMasher]

Tape some kitchen foil over the glass?

[TempTest]

I'd like the fridge to 'look' nice being as it'll be a permanent fixture in the kitchen, so if it *needs* to be covered I'll do it using some black film but if it doesn't need it I'd prefer it to remain transparent so I can peek in without opening the door... But not at the risk of compromising the brew. So what do you reckon based on it'll already have UV protection fresh from the shop? Environment described above

[alexlark]

I bet car window tinting film would look good on the glass of the fridge. You can get it in different shades of black too