Is my yeast harvest from a commercial beer working?

About 40 hours ago I emptied out all but 75ml of a 500ml Emerson's Weissbier. There was plenty of sediment on the bottom (and, of course suspended yeast too.)

I flame sterilized the bottle lip and added about 250ml of boiled, lightly hopped wort, then covered the top with aluminum foil that had been boiled for 20 mins or so, and have been swirling the bottle regularly ever since.

It's a little difficult to see through the brown glass, but at this point, however, nothing much seems to be happening. Should I be seeing anything? A mini-krausen in the bottle? Or bubbling? Or is this lack of obvious activity entirely normal?

Is there any way of telling if the yeast is propagating? Especially given the difficulties of getting liquid yeast in NZ, I'm planning on doing this again in the future, and want to make sure I'm getting it right.

Thanks for your help!

You could replace the foil with an airlock for a while. If you see bubbles (especially after swirling), it's working. You'll probably need to step up the starter at least once, and probably twice before you can grow enough to pitch with, and it takes a week or two, but I've done it many times in the days when you couldn't get decent yeast.

-a.

The Emerson brewing site says that beer is bottle conditioned and that they use Bavarian yeast in their brewing, so you may have viable yeast. Soeme breweries do use a different yeast for bottle conditioning than that which is used in fermentation. Shelf life, shipping conditions, and the percentage of alcohol can all impact viability,

Yup, I'm pretty confident in the yeast's suitability. I read that others have used the Emerson's weissbier for their own hefeweizens and had success with it. They definitely do bottle carbonate with the main fermentation yeast.

I am getting a few bubbles when I swirl, so I guess that's a good sign. I plan to step it up into a 1L mason jar and then use that to pitch with.

Hopefully, it'll work out for me too

I would think with such a small amount, you probably aren't noticing anything because the quantity of CO2 is so little. Doesn't mean things aren't healthy and active.

> Is there any way of telling if the yeast is propagating?

The classical answer would be to plate it out, then you will have visual confirmation (and can reculture from there).