The timing of when a harvest occurs is determined by the ripeness of the grapes in a particular vineyard. Winemakers measure multiple elements to determine ripeness: acidity rates, sugar quantities (which determine alcohol by volume), tannin levels, and simply whether the grape seeds taste good, all of which differ for every varietal. Even on the same vineyard, for example, Cabernet Sauvignon grapes will reach peak ripeness on a different date than Merlot grapes.
Winemakers must also consider the threat of inclement weather which, if deemed likely to occur sometime in the relatively near future, could accelerate the timetable of their harvest. In the Bordeaux region, harvests traditionally take place in the month of September but can begin as early as August and end as late as October.
A harvest can last between days and weeks depending on the size of the vineyard. The actual harvesting is either done by machine or by hand, but no one has fully automated the process yet, so humans are always involved to a greater or lesser degree. The process usually begins in the early hours of the morning, to minimize the chance that the sun’s heat will cause grapes to begin fermenting after they’re picked but before they’re crushed.
Bunches of grapes are shorn from the vines, collected in containers, sorted and de-stemmed (by hand or by machine) and eventually transported (by tractor or by horse) to a vineyard’s vats for crushing. The process is laborious and requires considerably greater numbers of personnel than a vineyard would normally need to employ.
Luckily, at chateaux across Bordeaux, visitors flock from around the globe, clamoring to volunteer for the right to engage in the manual labor (almost entirely unpaid) of the annual harvest. It is a special time of year, and these international groups of grape harvesters often feast and revel deep into the night, sharing culinary traditions, drinks and songs with the owners and staff of the vineyards, until sleep eventually beckons.