Is a 6 hour layover in Frankfurt long enough to leave the airport to get lunch?Is a 6 hour layover in Frankfurt long enough to leave the airport to get lunch?

I am flying from Bucharest to the USA, and I have a 6 hour layover in Frankfurt. Would it be crazy to leave the airport to have lunch and a beer? It sounds like a long time to me, but with passport control and airport exit and re-entry is it actually long enough?