* Chile December manufacturing down 2.5 percent year on year * Less workdays and fall in wine and chemicals output cited * December copper output down on ore grades, maintenance * Annual copper output highest since 2007 By Antonio De la Jara and Anthony Esposito SANTIAGO, Jan 30 (Reuters) - Chilean manufacturing production unexpectedly slipped in annual and monthly terms in December led lower by fewer working days, a fall in wine production and less output of chemicals and certain metals, the government said on Wednesday. Manufacturing output fell a seasonally adjusted 2.5 percent in December from November and also dropped 2.5 percent from a year earlier, the statistics agency INE said. It was the second time in 2012 the index fell versus the prior year. "This drop is mainly due to reduced production of common metals such as ferromolybdenum (an iron molybdenum alloy) ... and chemical substances. Also, we observed a specific slip in wine production," INE said. However, wood pulp output and demand for metallic structures in mining projects remained strong in December, the government added. INE said the drop in manufacturing production had also to do with a high base of comparison, apparently referring to manufacturing in December 2011. A Reuters poll saw the manufacturing index, which is broadly comparable to the prior industrial output index, growing 0.9 percent from a year earlier boosted by food and beverages production. "We believe the continued decoupling of supply and demand sector data will continue to be a key element to consider in light of the local economy's signs of overheating, which could bring greater inflationary pressures in the medium term," brokerage Banchile Inversiones said in note to clients.