Chances are it's SS, not aluminium
. (Oh no, where's Laughing Gnome? They do have a good point though... we don't say "titanum" or "uranum".
You could just turn it upside down and cut a hole in the top (formerly bottom) and make a lid that seals it with a hole for an air lock. Then attach/weld valve(s) at the bottom (formerly top) to the hole. But this wouldn't be ideal because the angle of the "cone" would be awfully shallow.
Welding an SS cone to the bottom is theoretically possible, but it would need to be a very clean weld to avoid nooks and crannies for bacteria to hide.