Wine Faults
Dr. Jeffery Snow - 11/2/2025
Wine Faults
I always hope that each time I extract a cork, a delicious wine - free of any notable faults, will spill into my glass. Thanks to the enormous improvements in viticulture and winemaking over the past 63 years of my direct observation (yes, I began drinking wine at home at age 16), it is almost certain that my hope is fulfilled. But faults are common in the wine world – though I am referring to geological ones, not the liquid in the bottle!
Recently I happened to look at a map of the San Andreas Fault and noticed how many wine-producing communities lie along its route. Touring California wine country in the 1980’s Julie and I encountered a few earthquake damaged structures at older legacy wineries. We especially remember an impressive historic round stone “tower” at the Joseph Phelps winery. Although it had only suffered minor damage it was deemed structurally unsafe and was eventually torn down; it’s loss removed a visible reminder of the long history and heritage of California winemaking.
Despite the risks and dangers of repeated tremblers, the wine industry there keeps growing and expanding. Of course their wonderful Mediterranean climate, ideal for winemaking, is the primary reason they eschew dangerous ground movement and farm grapes so enthusiastically. In spring the early buds are safe from frost damage. Quite reliably there is just enough rain, but rarely does it fall during harvest. And, if it does rain, warm dry winds follow and save the grapes from the damaging effects of dampness; plenty of sunlight hours to perfectly ripen grapes. And unlike many kinds of farming where crop failures do occur, wine crop failure is essentially unheard of in California; a vigneron can reliably produce sound wine essentially every year.
And I’m talking about not just a reliable harvest, but one that makes for especially delicious and flavorful wine. Winemakers attribute these extra layers of flavor to the various minerals found in plumes which erode from hills. They may be volcanic or from upthrust ocean bottom, by earth movement associated with fault lines. Earth movement continuously refreshes the soil with stone pulverized against stone and upthrust volcanic soil. Erosion from the hills of this mineral rich material provides a steady supply of important trace minerals which continually feed the vineyards below. Napa Valley has many such areas where grapes a few rows over on similar looking terrain are quite different in flavor due to subsoil of differing minerality due to narrow erosion plumes of mineral rich rock.
Indeed, a Mediterranean climate ensures that California can produce excellent wine consistently. But for those special terroir specific nuances look not to the sky and weather but to the trembling ground. Indeed, we want faultless wine, but geological faults and associated ground movement can provide richly varying minerality yielding wines with unique flavors tied to that land.
So, I believe geologic faults are a key component of a wine’s terroir. Each of us is drawn to distinct flavor profile—unique yet subtle variations that we seek out for our personal enjoyment. Faults help define the character of a terroir, and the character of a wine like those that come from the San Andreas Fault regions. The terroir we love with specific minerality can give each of us our ideal wine due to a specific minerality arising often from faults such as the San Andreas.
NOTES:
1) Harding, Julia and Robinson, J.: The Oxford Companion to Wine, 5th edition, 2023, Oxford University Press, Pages 277 -278.
2) Hamilton, Megan, Operations Manager, Joseph Phelps Winery, Napa Valley, Personal Communication.