About a year ago I bought various titanium offcuts and had a go at the anodising trick. Electricity and a phosphoric acid solution let you turn the surface of titanium different colours, and the finish is very hard-wearing. "Rainbow titanium" gizmoes (like the pen I review here) are common these days.
The easiest way to get your hands on dilute phosphoric acid in this modern world is to use cola, since all cola contains phosphoric acid for flavour. Diet cola is preferable, since it's less sticky. I used Diet Coke.
There was plenty of cola left after I'd satisfied my curiosity about anodising, so I put the excess in a ground-glass-stoppered bottle. It's been sitting in the kitchen next to my radiometer, looking all sciencey, ever since.
There is, by definition, very little food value in a diet drink.
But something still, eventually, managed to grow in the bottle:
I'm not sure what's feeding the mould, but I presume it's the "caramel colour" that's number two on the Diet Coke ingredients list.
Ordinary caramel is just sugar that's been browned by heat, and obviously has plenty of food value; Diet Coke may have "less than one calorie" per can, but they're talking about the dietary "large calorie", which is quite a bit of energy. I think the "sulphite ammonia caramel" that's used in acidic soft drinks is much the same, energy-wise, as plain burned-sugar caramel.
If it were just the caramel, though, you'd think that the mould would have grown in the unsterilised bottle quite soon after I'd stoppered it up and left it where it could soak up the morning sunlight every day.
The sunlight may have something to do with why the cola is the colour that it is, too. It's much paler than it was when I first bottled it, and I noticed the colour change long before I noticed any mould.
I suppose the acidity of the cola could have retarded mould growth. Perhaps the breakdown of aspartame into its constituent amino acids (due to the action of the acid, and possibly the sunlight again) had something to do with it.
Or maybe Aristotle was right.
16 September 2007 at 11:15 am
Be careful, anything that grows on Diet Coke strikes me as likely to be a potent bio-weapon ;)
16 September 2007 at 9:06 pm
I wonder if that stuff growing is photosynthetic. If it is, then you wouldn't necessarily need anything with nutritional value in order for the mold or fungus or algae or whatever it is to grow. It gets its energy from outside the closed system, and uses that energy to....do something with the remnants of the diet coke.
16 September 2007 at 11:25 pm
I grow on Diet Coke. And that seems to defeat the whole diet thing. But it could be the beer and pizza as well. Ah well, more experimentation is called for.
18 September 2007 at 2:03 am
Rich, I am becoming concerned that you may actually be my doppleganger. We frequent the same net neighborhoods and now it appears that we may have much the same diet.
That being said, I not only drink too much Diet Coke but I use it as a cleaning agent for the few chrome parts on my motorcycle - it does a suprisingly good job of removing road grime. I've also experimented with seeing if anything would spontaneously grow in DC but I guess I just didn't have the kind of patience that Dan does - I threw out my sample after just a month or so with nothing growing yet. I do mean nothing as well - I examined it under microscope and it was devoid of all signs of life.