Intersting colour changing Chemical reaction

[Wolverine]

Ok I hope someone can answer this this is the full story
I inherited an old ( 1980's ish ) by the look of it Harris quick fine filter kit. I decided to clean the filter bag by soaking it in vwp for an hour it came up very clean and I assume sterilised I rinsed like mad and use it to filter some wine and it was rubbish but that's another story
I've just gone to use the kit again to strain some ginger beer and thought I quick soak in some videne would be enough to sanitise the filter bag and guess what .........
It immediately turned purple ???? any ideas?
I'd Love an explanation

 

[Wolverine]

Come on chemistry geeks! its driving me mad the colour was like UV so my mind is thinking somehow the videne solution somehow changed the way light was being reflected off the fabric. I wish I had a UV bulb to see if it glowed or something

I used the bag in the end anyway and it's now returned to white ????

 

[alanywiseman.]

Interesting :hmm:

When did it return to white? did you rinse it and if so what colour was the water that ran off the bag?

 

[Wolverine]

yes I rinsed it and the water ran clear and the bag remained purple so that's why I used it anyway and it was after I poured the ginger beer in that the bag returned to white
There is. NO purple colour at all in the strained ginger beer

 

[alanywiseman.]

I have not used videne but was the water hot or cold?

Videne is a povidone-iodine based steriliser so it sounds that the iodine has been released quickly and as a result the bag turned purple (you would not notice this if sertilising glass or FVs though as the water is not absorbed). THe iodine many have been relesed due to starch on your bag.

I believe that the purple clour will have disappered because as your beer flowed through any molecles with unsaturated (double) bonds will have been reduced by the iodine and as a result the iodine will have bonded to thoughs molecules. This means that the iodine would have no longer been purple in colour.

Does any if that make sense? :hmm:

 

[alanwh]

Yep thats right I remember from way back iodine changes to purple in the presence of starch ?

 

[calumscott]

Yup, iodine is the standard test reagent for starch - O grade biology, remember it well!

So by that token, your filter bag had some residual starch, the videne when sprayed onto it either has molecular iodine or molecular iodine was released from some reaction, this then reacted with the starch to give you the purple.

Run a pile of water and alcohol through, both of which I believe are solvents for starch and so it's gone from the filter into your beer. Alan's assertion that stuff in the beer may well have been a better bet for the iodine to stick to is totally plausible - iodine in compound with something else (indeed in solution) will of course be a different size and shape and therefore reflect and absorb different bits of the spectrum.

Exactly what's happened? From here your guess is as good as anyones! :)

 

[Wolverine]

cheers guys I should have been able to have got that myself having a level biology ha ha

Will the starch in my brew do any harm ?

 

[calumscott]

Doubt it, I can't imagine there would be much of it...

Question is though...

...where did it come from? Wine wouldn't have had any would it?

 

[alanywiseman.]

The starch wont be in your brew. What I think is in your brew is molecules that now have bound iodine. Generally speaking iodine is not a healthy thing to ingest. I would not chuck the brew out just yet though. You made need to look into it a bit further to see if the iodine is in your brew or not and if it has entered how I suggested above whither during the digestion process it will be released.

Just to clarify the colour change from purple to back to normal happened as you poured your ginger beer through your filter bag?

 

[alanywiseman.]

Run a pile of water and alcohol through, both of which I believe are solvents for starch and so it's gone from the filter into your beer.

The issue with this is that if the filter was rinsed in water and the colour did not change back to normal then the water has not removed it. IMO it is more likly that the iodine on the filter have now reacted with unsaturated bonded molecules in your brew. I dont think it has simply just dissovled in the water/alchol sovent mix.

 

[Wolverine]

Yes the colour chanes back when I poured the brew on to the filter I'm not gonna chuck it it was a 1.25 ml per liter solution of videne and it was a 5 gallon brew so it will be well diluted