[Wine] how do you stop an instance (prefix)?

[mrmedia]

env WINEPREFIX="/home/linux/.wineinstance1" wine
env WINEPREFIX="/home/linux/.wineinstance2" wine
env WINEPREFIX="/home/linux/.wineinstance3" wine

How do I ensure that instance3 is not running? Turn it off and on? 
i.e. install risky software on trial - but then turn off the instance until next time it is needed for testing?

i.e conserve resources by stopping the OS instance. 
I guess it does not use much until you run an app in that instance after a boot up - but the dotnet stuff is an added risk

I guess it is easy to delete the instance but can it be turned off?