As I mentioned earlier, late harvest wines are most easily confused with wines that undergo drying after harvest. The biggest difference between the two is the state of maturity the grapes achieve.
With late harvest wines, the grapes go through their full growth cycle and then some, becoming super sweet but at the same time losing some of their acid as they get super mature. Dried grapes, such as those that go into Amarone, are picked at various stages of maturity. Most often they are picked when they are just past ripe, fixing the ratio of sugar and acid in the grapes even as they dry and thus fixing the ratio within the wine.
So why are we talking about late harvest wines then? Because ZInfandel is ideally suited to produce a late harvest wine. How so? Zin is one of the few grapes that ripens totally unevenly. Cluster at harvest will often have both raisins and green berries showing. Leave them on the vine and you get more raisins and fewer green berries. Those green berries are so far behind the bulk of the fruit on the cluster that even at a late harvest stage they supply superb acidity to the rich sweetness a late harvest Zin is capable of!
Photo courtesy thegourmetro via Flickr/CC