Allowing vines to produce too many grapes, resulting in wines that are hollow, watery and characterless. *
Grapevines are fussy things. Normally they just want to take over a small region of the planet and be left alone. But grape growers have other plans. They want grapes. An orderly vineyard might be nice too. So they plant in rows and prune the vines to keep down their prolific growth. Interestingly, when challenged this way, grapevines tend to produce more grapes – and that’s good for the grower. But at a certain point, the vine produces too many grapes, or at least too many to produce a quality wine.
For the grape farmer there is a trade off. Increase the yield and there will be more grapes to sell. But that lowers the grapes’ quality. In an environment where grape prices are fixed, that can be bad for the wineries that purchase grapes. If grapes are priced the same, then a ton of grapes costs the same regardless of quality. There is no incentive for the grower to increase quality since quality costs a lot to produce but would not result in a better price for the grapes. For the lowest quality of wine, this may be OK (it is far from actually a good thing) but it is impossible to make great wine from over-cropped grapes.
In an over-cropped situation, the vine has to parcel out nutrients equally. Whether the vineyard is targeting 2 tons per acre of 10 tons per acre, the vine can only deliver the same amount of nutrients. In general, you’ll find quality wine made from low yield vineyards – the 2 tons-per-acre is typical – and cheap bulk wines from the 10-tons-per-acre crops and some times more.
What constitutes low or high yield depends on a number of factors, and principally the grape variety. Some grapes can produce top quality at higher yields while others must be severely restricted. The corollary is that over-cropping is also relative, as far as the actual tonnage per acre goes, and varies from grape to grape. But whatever the ideal yield is for a given grape and terroir, over-cropping is over-cropping and the result is almost always a wine that is “character challenged”.