You could probably make something that approximates it, but it wouldn't be the same. That cake culture they use is basically a controlled infection of the media (in this case, a tea and sugar solution). Normally, yeast will ferment this mixture, using the sugar and turning it into CO2 and EtOH (ethanol). however, different bacteria and fungi will work faster than the yeast, and have all sorts of funky byproducts (all the acids the website talks about). You could accomplish the same style of beverage by mixing up about 7 lbs of sugar and 5 gallons of tea, and leave the top off the bucket and let it sit outside with some cheesecloth over it to keep bugs out. the problem with this is that there are all sorts of regional variants to airborne yeast, bacteria and fungal cells, so the ones you end up with may or may not ferment out something drinkable. more than likely you'd end up with something about the consistency and taste of week old baby vomit (which is what happens when you screw up brewing beer and the wash gets infected....gross. With wine its not so bad, you usually just end up with vinegar - acetic acid). But, if you decide to try it, let us know how it goes.
