To set the stage, let’s define what a vacuum is. A vacuum is a closed system in which pressure is less than atmospheric. In order for this to happen, you need a constant amount of space (i.e. a rigid container) where air particles are removed. There’s a lot of airtight containers/bags out there that get rid of some air, but these aren’t necessarily a true vacuum. An easy way to tell if you don’t have a vacuum container is if your container shrinks (i.e. is it a bag or does it have a lid that collapses into the container). If your container shrinks, it is not a vacuum and will not decrease the pressure below atmospheric.