There is no visible extra security in Brussels that would slow you down.
Check this page for the expected rush at the airport for your day of travel.
So yes, get on a train, get off at Centraal, visit the Grand Place, head back to the airport and have a beer after security if you really have to. You can also buy beer in the tax-free shops at the airport and take it on board with you (but the airline will not allow you to drink it). Also, if you connect in the US, you will not be allowed to take that beer with you.