Once grapes have grown, determining when and how to pick them has a critical impact on the final wine. One technique is to measure grape sugar levels, called "brix," with a brix meter to determine ripeness, but farmers also taste the grapes to assess development of flavor compounds found in grape skins called "flavonoids." Farmers may disagree on the best time to pick or may choose to pick earlier or later to foster a particular style. If they want higher acidity and lower alcohol, farmers pick early. Waiting, however, may yield greater complexity and higher alcohol, and grapes may still retain acidity if the weather is cool.
The age of the vines also is a key factor in grape quality. Vines under three years old don’t produce much, if any, fruit, whereas old vines are prized for producing complex fruit but yield far less. The optimal age of a vine for producing top quality is a subject of debate, however. Some say "the older the better," while others maintain that quality declines after a certain age.
Once farmers separate grapes from the vine, the race to the winery begins, because temperature and exposure to oxygen can deteriorate quality. Handpicking offers gentile treatment, which prevents oxygen exposure if bunches are collected without breaking many of the skins open, but it also takes longer. Mechanical harvesting is quicker but not as gentile. In some places, such as the steep slopes of Germany’s Mosel region, mechanical harvesting isn’t an option. In any case, farmers often pick early morning or even at night during cooler temperatures and quickly move to the winery where grapes are sorted from insects, leaves and other debris and prepared for processing.
