In general if it tastes OK and doesn't have visible growths (e.g. fuzz, green or white patches) then it's fine. A lactic acid fermentation will actually kill most pathogens, so it's surprisingly safe.
The yeast and other lactic acid bacteria are coating (and usually inside) the produce, so you don't need to worry a lot about "the right culture". (If you want to be sure, you can collect a starter culture, but that's quite advanced.)
The yeast and other lactic acid bacteria are coating (and usually inside) the produce, so you don't need to worry a lot about "the right culture". (If you want to be sure, you can collect a starter culture, but that's quite advanced.)
Source: I make beer.
More authoritative source: http://houston.afdo.org/uploads/1/5/9/4/15948626/1000_jay-ne...