My understanding is that the light-induced skunking is due to downstream products initiated by the photodissociation of iso-alpha-acids by ultra-violet light, a mechanism that was discovered in Ghent University in Belgium. It occurs quite quickly with uv light at a wavelength of 250nm (UVA), and is much slower at 300nm (UVB), and disappears completely at longer wavelengths (UVC). Plastic fermentation vessels are typically made from polypropylene or HDPE, and some of the clear plastic carboys are made from PET. The uv transmission of all these materials is high at 400nm, but drops to practically 0% as the wavelength shortens to 350nm, and stays that way at shorter wavelengths. Untreated clear glass, on the other hand, has quite high UVB transmission, and so would present a problem for skunking. So, the conclusion is that skunking from within a carboy is nothing to be concerned about as plastic fvs completely block out the wavelengths of light that cause it. :thumb:
