Vacuum packaging is not always used. I keep mine in the fridge (wine yeast) but I have seen several LHBS's just keep it on the shelf...it has a long shelf life, longer if kept refrigerated (2-3 years).
Something is always fermenting....
"It's Bahl Hornin'"
Kegged: Sour Saison, Pale Ale, Aggie Ale, Firestone DBA, De Koninck Blonde
Bottled: Belgian Quad (Grand Reserve), Derangement (Belgian Dark Strong)
On Deck: Pliny the Younger