WILTINGEN, Germany — In the bright, cavernous basement of the new Van Volxem vinery building, Christoph Dirksen, one of the Mosel region’s most important wine tasters, was making his rounds sampling from giant stainless-steel tanks.

It’s early to make a final judgment on the wines of 2018, even for Mr. Dirksen, a critic for Vinum, an industry publication. But he nodded his head approvingly. Here, and almost everywhere else in the country, German winemakers are celebrating what they believe will prove to be a banner vintage.

“It’s not just good,” said Roman Niewodniczanski, one of Germany’s most celebrated vintners and the owner of Van Volxem. “It’s grandiose!”

What proved to be the country’s hottest, driest spring and summer on record were disasters for many German farmers, river boat captains and foresters. But they were a blessing for winemakers, leading to a record harvest — Mr. Niewodniczanski estimates his output will be up 20 percent or more on last year — while also imparting a high must weight: the all-important measure of a grape’s sweetness.