What difference does altitude make to a vineyard?

Hello there! I'm Dr. Vinifera, but you can call me Vinny. Ask me your toughest wine questions, from the fine points of etiquette to the science of winemaking. And don't worry, I'm no wine snob—you can also ask me those "dumb questions" you're too embarrased to ask your wine geek friends! I hope you find my answers educational, empowering and even amusing. And don't forget to check out my most asked questions and my full archives for all my Q&A classics.
Dear Dr. Vinny,
Why do winemakers valuate the altitude of their vineyards? Is there any difference or comparison to sea level?
—Carlos, Porto Alegre, Brazil
Dear Carlos,
The biggest difference in wines from high altitudes is the climate; it is generally cooler (especially at night) than at lower elevations. This translates to a longer growing season, allowing the grapes to ripen slowly and evenly, often at lower alcohol percentages. There is also frequently a difference in soil type; high-altitude vineyards often have poorer, rockier soils, with fewer nutrients and better drainage. Together, these factors often result in smaller berries with thicker skins, thus producing lower yields and more concentrated, tannic wines.
Logistically, mountain vineyards can be a nightmare. Water, electricity and roads are hard to engineer. Steep terrains are difficult to develop, rocks get in the way, the wind whips around and the soils can be less fertile. It's quite an accomplishment to get a high-altitude vineyard. So sometimes when a winemaker is talking about the virtues of their high-altitude vineyard, it could be they are simply proud of putting in the effort to cultivate one.
—Dr. Vinny