listeria is apparently very rare. So, maybe a treat if you really have to. Melt abit of creamy vanilla ice cream - tastes very similar.
Apparently the prob with soft serve machines, or any type of drink machine where they pour liquid straight from it (like ice slushys etc i guess) is that they dont wait till it is empty and clean it out, they just keep retopping it, so there is always old stock mixed with new stuff.
Please anyone, correct me if i am wrong, but, thats what i have been told.