This summer when I soak bratwursts in stout beer, I'll say it's for the health benefits. Beer-bathed pork formed fewer potentially cancerous chemicals than non-marinaded pork when grilled close to hot charcoal in a recent experiment by Portuguese and Spanish chemists.
Black beer, like a stout or porter, proved more effective than pilsners at preventing the formation of polycyclic aromatic hydrocarbons (PAHs), worrisome chemicals formed in smoked and grilled fatty meats. The European Union regulates levels of PAHs as potential carcinogens, following concerns raised in a 2002 report by the European Commission's Scientific Committee on Food.
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The beers' alcohol wasn't knocking out the PAHs. Even meat marinaded in non-alcoholic beer held lower PAH-levels than plain pork. The chemists suggested antioxidants in the beer may interact with the surface of the meat and make it chemically resistant to PAH formation.
The scientists soaked pork loin steaks for four hours in three different beers. Another set of steaks remained un-marinated. After four hours of soaking, the chemical reactions on the meat surface had mostly stopped.