TRAVERSE CITY — Wine grape harvest will soon be underway in the Grand Traverse region.
Over the next month and a half, the fruits of a whole year’s labor will be picked, crushed and pressed, starting the process to create the 2013 vintage of the fine wines of northwest Michigan. The optimal date for picking a particular variety will be determined by a number of factors, including the genetics of the variety, seasonal weather conditions, site characteristics of the vineyard, progression of fruit maturation, threats of fruit loss to pests and diseases, the onset of freezing temperatures, and the style of wine to be made from the fruit.
As with most types of fruit, there are many different varieties of wine grapes and each one of them has a typical ripening season. Chardonnay will typically ripen a few weeks before Riesling, no matter where it is grown. In our area, the earliest varieties are usually ready for harvest by early September; the harvest of late varieties may last into early November. The 2013 growing season has been a cool one which will likely result in a slightly later harvest than normal for all of our varieties.
Based on degree-day accumulations (mathematically derived from daily maximum and minimum temperatures), this year’s season is running about a week behind average and a number of weeks behind the hot 2012 growing season. For example, at the Northwest Michigan Horticultural Research Center in Leelanau County, a variety called Frontenac was harvested on September 6 in 2012; this year it was ready for harvest on September 18th. Vineyards that are situated on south or southwest-facing slopes tend to accumulate degree-days more quickly than other sites, which can lead to an earlier harvest.
Sometimes problems come along that can force a vineyard manager to harvest the grapes earlier than was planned. If threats of high levels of fruit rots, insect injury or depredation by birds develop, fruit may have to be harvested in quick order to avoid a significant loss of quantity or quality. An early killing frost can result in no further ripening of the fruit and the threat of fruit dropping from the vines, so the fruit would need to be harvested soon thereafter.
Different wine styles call for fruit with slightly different ripeness characteristics. Grapes can be harvested a couple of weeks earlier than normal if they are going to be used for sparkling wines. If a sweeter dessert wine is the target, the fruit may have to be held on the vine for a few extra weeks at a significant risk of loss to pests and diseases. For ice wine production, the fruit must remain on the vine until a sufficiently cold day comes along to meet the ice wine criteria- the fruit must be at a temperature of 17 F. or lower at harvest.
This may mean waiting all the way until December or January to bring in the crop.
Erwin ‘Duke’ Elsner is a small fruit educator with MSU Extension.