They can't stop it. Any article that can be legally sold in one EU country can be sold in the others - no national law may prevent this*

The "Reinheitsgebot" were in breach of Article 28 EC as they prevented the importation of beer from other EU States, thus the ECJ declared them incompatible with Community Law.



http://en.wikipedia.org/wiki/Reinheitsgebot

Article 28 EC:

"28. Quantitative restrictions on imports and all measures having equivalent effect shall be prohibited between Member States."

*there are certain exemptions, none of which apply here.

True, but they aren't classed as beer, they are "inferior" products.

All the major German breweries still brew to the Rheinheitsgebot - with the exception of wheat beer.

It also means thing like Cab are sold as alcopops, not beer derivatives.