For one of the beers I needed a Brettanomyces yeast and thanks to the wonder of the internet I got a culture from a home brew shop. The culture was in liquid medium, which I have to say made me a little wary. With liquid cultures all you get to see is a turbid suspension, but you have no idea which organisms might be in it. Before I used it for brewing I thought it prudent to streak it out on an agar plate so I'd be able to look at the colonies of whatever was in there and see if they were what they were supposed to be. It was a good job too, as when I stuck a loop in the vial I could feel there was something a bit solid in there, most likely a filamentous fungi. I streaked it out and sure enough what mostly grew was mould.
On the plus side there were some yeast colonies in there as well, and thankfully some of them had separated out from the mould (the dots on the right). I picked a couple off and subcultured them onto a fresh plate with gratifying results:
The culture is a bit older than in the first picture so the yeast colonies are larger but I think the difference in pretty clear. I've saved the Brettanomyces on an agar slope as I don't need it just yet but I now feel confident about using it.