Hot days, cold nights—lodestone of quality wine.

Terroir involves many things, but diurnal transition is essential for quality. Hot days allow fruit to drink in sun and develop fruity ripeness. Cold nights allow fruit to develop necessary balancing acidity.

When a vineyard enjoys that gift—hot days, cold nights—the vineyard bears wonderful fruit that can be made into superior wine. It is the reason Napa and Sonoma with their sun-drenched days and chilling Pacific morning fogs are American royalty in wine production.

It is the reason Texas High Plains around Lubbock are dynamo of the Texas grape growing engine, just as the hills and near-desert country in Washington and Oregon are ascendant. It is why cool, steep, sun-soaked hillsides of the Mosel River in Germany make quintessential riesling, and high altitudes of Argentina and Chile deliver astonishingly good wine at astonishingly good prices. Also why Finger Lakes region of New York State and providences in Canada make fabulous riesling, cabernet franc, and sparkling wines.

You certainly can grow grapes in lesser circumstances. California’s warm Central Valley produces massive amounts of grapes whose juice fuels boxed wine industry and delivers bulk for lower-shelf bottles. There is nothing blatantly bad with such commodity wine, but also nothing outstanding. Days are warm, sun abundant, nights sadly sultry. Great for grape growing; for fine wine, not so much.

Wineries can conjure magic in the cellar, but excellence starts in soil and toil of a farmer—especially when graced with the gift of hot days and cold nights.

Tasting notes:
• Toad Hollow Vineyards Eye of the Toad Dry Rosé of Pinot Noir 2016: Fun summer sipper, bone dry, pairs with vegetarian fare, beautiful color. $12

• Llano Estacado Cellar Reserve Texas Tempranillo 2014: Simple easy drinker, plenty of fruity sweetness; slurp and enjoy from Texas High Plains. $14

• Nik Weis St. Urbans-Hof Estate Riesling QbA Old Vines 2015: Mosel off-dry that drinks drier than it is; shows how slightly sweet riesling is strikingly delicious, and a great food wine. $15

• Argyle Vintage Brut Sparkling Willamette Valley 2013: Dry, crisp, bright, well-done méthode champenoise sparkling. $19

Last round: I’m giving up wine every day all month. Wait, wrong punctuation: I’m giving up. Wine every day, all month.

Email Gus at wine@cwadv.com. Facebook: Gus Clemens on Wine. Twitter: @gusclemens. Website: gusclemens.com.