There is what menus in the better restaurants promote as fine aged beef and then there's what customs agents stopped at Bulgaria's border with Greece one day late last month. According to news accounts, a three-truckload shipment - roughly 75 tons in all - once might have been waved through on its way to the processed-food industry for salami and other deli delights. But under pressure from the European Union, the former Soviet Bloc nation has been tightening its meat-safety standards lately. And so this one was subjected to a careful inspection, if only because the accompanying paperwork wasn't entirely in order. It failed - spectacularly. Now, Bulgaria's processors are known for importing old meat, but this was so elderly that it had turned bluish purple . Customs agents traced it all the way back to the Republic of Ireland, whose veterinary service records showed it had been packed "around 20 years" ago. The shipment subsequently was impounded and has been turned over to the Agriculture Ministry in Sofia, which says it probably will be popped into a nice, hot oven ... where the next color it assumes will be black.