Chris Hogg wrote:

Not convinced by the image, which looks like coarsely crystalline
sugar.

videos elsewhere show the 'grains' rising and falling as they carry CO2
to the surface of the fermenting vessel, I don't remember the one we had
doing that, it was just a fine beige "silt" in the bottom, that was
stirred up at the start of each batch and had sugar, lemon juice and
powdered ginger added.

It would seem that 'alcoholic ginger beers' are made by the
traditional method, using the yeast/bacteria combination. Crabbies is
one such, apparently. Unless they sterilise it or micro-filter it, I
would have thought there would be enough traces of the 'plant' in such
GB so as to be able to start your own, with a little patience.

Might be an interesting experiment, but teh internet variously suggests
it is flash pasteurised or cross-flow filtered