As I worked as a microbiologist for many years I do feel slightly embarassed when I have to buy some dried yeast for homebrewing. So I've been trying to sort out for myself some brewing yeasts taken from bottle conditioned beers where I know the primary strain is used for bottling too.
First up was Hop Back from a bottle of Summer Lightning. I've used this before and it grew well on the agar plate. My latest brew was made using this culture, and the fermentation went fine. Tasting notes will be posted when I start drinking it.
Next I cultured the sediment from bottles of Fullers 1845 and Sierra Nevada pale ale. The Fullers yeast has been depressingly feeble though.
You can just about make out two small yeast colonies, as well as a fungal contaminant and a bacterial contaminant at the top.
As I had to incubate the plate for so long some contaminants have started growing. With a bit of experience it's pretty easy to identify what's growing on your agar plate from the shape of the colonies without having to look at anything under the microscope. In this case though, as I had so little growth, I popped into the lab for confirmation.
Fullers yeast at x 1000 magnification
If you don't have a microscope set up with a camera you can take pictures by carefully holding a digital camera above the eye piece. The picture above was done on my mobile phone and you can just about see the yeast cells.
Here the bacterial contaminant - large rods of a Bacillus sp.
As I'm happy that even from the poor growth I have got some brewing yeast I've sub-cultured it on to an agar slope and I'll used it to brew with soon.
Quite why there were so few viable yeast cells in the bottle of 1845 I'm not sure.
Sierra Nevada yeast culture
The Sierra Nevada culture pictured above was actually set up a few days after the Fullers one and shows much better growth. Perhaps the 100 day maturation process that Fullers proudly declare on the bottle means the yeast is more knackered.