Yup, it's a 500 gr Passata bottle.
I actually spun up 2.5 litres after smacking the pack, then discarded the beer, and transferred the yeast into the bottle. I spun another 2 or so litres with about 20% of the first growth, and the bottle is the combined result after discarding the starter beer.
I pitch and ferment lagers at 9ºC, so I need lots of yeast.