Hamm's Beer Porcelain Cork Cap..."Hamm St. Paul" with eagle embossed

I have two two original porcelain Hamms beer cork caps. Embossed on the top is Hamm St Paul and with an eagle in the middle. I grew up one block away from the main plant in St Paul and so these were special to find. I know nothing about them. Does anyone know about what era they might be? The corks are a bit eroded, but stil there. Also, there is a opening from one side to the other on each cap. Thanks for whatever info you can provide. For me it's great neighborhood history.