September-October every year
The end of summer and the beginning of autumn are synonymous for harvest: the grapes are ready to harvest and produce the wine of that year. In this period it is common to hold numerous popular festivals.

Between september and october, the harvests, which in areas of the Douro, are large areas that require some labor, but in my case, or better of my family, the vineyard is quite small, whose final product is for own consumption; and it is a pretext to gather friends and have a lunch.


Just one more detail: from the must is made the brandy (a drink with high alcohol content) and jeropiga (traditional from my country), which is a preparation by adding brandy to the grape must to stop fermentation, resulting in a more alcoholic drink than wine (I personally do not appreciate) which is the traditional drink for magustos (see next link)
https://someanywhere.blogspot.pt/2015/11/magusto.html