THE logic behind Foster's carving off its wine arm into an independently listed company was confirmed yesterday when fresh figures from the Bureau of Statistics showed sales of local wine were suffering their most protracted period of weakness in 15 years. The downturn is tipped to be made all the worse by a bigger-than-expected domestic vintage harvest this year. Production of 1.62 million tonnes is an increase of 1 per cent on last year, adding to the already bloated stockpile on which many Australian winemakers are sitting.