When the temperature is from 15-18 degrees Fahrenheit for 24-48 hours, it's time to harvest grapes for ice wine. The conditions were reached for the ice wine harvest at Michigan's Chateau Chantal winery and for three hours, in single-digit temperatures, workers harvested grapes of the riesling, or riesling relative, varietal in an area that spans about an acre. The grapes, which will have about twice the sugar as grapes harvested during warmer months, were taken from the vines and placed into bins before being transported into the cellar to be pressed.