If you ever have the opportunity to get out into the vineyard and pick wine grapes during harvest I urge you to participate. My wife and I did just that several years ago and it is an experience we will never forget. We picked on a beautiful sunny morning but in reality, most wine grapes are harvested at night to take advantage of the cooler air lowering the temperature of the grapes. Most of the well-known wine-producing regions of the world are located in areas that not only have a climate favorable to viticulture but a phenomenon known as diurnal shifts. Diurnal shifts are when there is a significant change in the ambient air temperature between the day and night. A good example of this would be if you have been outside all day wearing only shorts and a tee shirt but need to wear a sweatshirt and long pants after dark, then you have experienced a diurnal shift. 

Sunshine allows a grape to increase its sugar content until harvest but in contrast, a grape’s acidity level decreases as it nears harvest. It can be argued that when grapes are cooled nightly sugar and acid levels are kept in balance creating a more complex wine. The diurnal shift phenomenon can be the result of different factors. In Napa Valley, it is the Pacific Ocean, the Rhone Valley has the mistral winds, and Duncan Savage proudly told me that his Cape Town, South Africa vineyards are “clapped” by winds off the Atlantic Ocean. 

Now that we know how grapes arrive at their peak to be harvested the obvious question is “What are the advantages of picking them in the cool of the night?” 

The first and foremost reason winemakers pick at night is to capitalize on the lower temperatures that are advantageous to producing superior wine by preserving the quality of the grapes that will be processed immediately after being taken to the winery. Grapes that have been cooled by the night air have more stable sugar levels, firmer texture, and less oxidation. This is very important when making white, Rosé, and sparkling wine but is also desirable when making red wine. Picking at night also enhances the grape’s fruit flavors and aromatics while giving the winemaker better control of the fermentation. The grapes are cooler when they come into the winery and don’t need to be cooled down before starting the winemaking process. 

I have included these two links on YouTube that give us a glimpse of what harvesting wine grapes at night looks like. One video is of grapes being picked by hand and the other with a mechanical method.

https://youtu.be/ujn8N6iBRng?feature=shared Hand harvesting

https://youtu.be/we5XNeuvn1c?feature=shared Machine harvesting

 You can find more videos on YouTube by searching “harvesting wine grapes at night.”

Since it is late summer and harvest is upon us, now is the time to call your local vineyards and ask if they could use help picking their grapes. For a wine lover, it is an experience you will not soon forget.