SOLICCHIATA, Sicily — When a writer comes calling, most winemakers would consider it in their best interest to offer their proudest efforts for sampling. But Frank Cornelissen has never been like most winemakers.

Instead Mr. Cornelissen, who has a reputation as the most unyielding of natural winemakers, thinks it’s more instructive to taste his failures. This explains how we came to drink his 2006 Magma Rosso, made from old nerello mascalese vines grown organically in the foothills of Mount Etna, as we sat in a restaurant in June outside this small town on the north face of Etna.

Magma is his top wine, made virtually by hand and aged in terra-cotta amphorae buried in volcanic rock. It’s made without additives, filtering or sulfur dioxide, the preservative used in almost all conventional wines. New vintages sell for around $250.

The 2006 vintage was very warm on Etna, and the wine showed the effects of the heat. It was overpowering, above 17 percent alcohol, and though it was indisputably complex and concentrated, with the aromas and flavors of dried cherries and minerals, the heat of the alcohol made it hard to enjoy. It also showed quite a bit of volatile acidity. Not a failure, maybe, as the wine has received positive reviews in the past, but not a long-term success, either.