This is the sort of mystery that remains at the heart of good wine. Why does it taste like this? Even if we can’t answer with certainty the questions posed by Chablis, we can’t deny the evidence of our senses. For many readers who did their Chablis homework over the course of the last month, briny oceanic flavors were a theme.

“One has the impression of smelling a (ideally Jurassic age) tidal pool,” wrote Carl Steefel of Berkeley, Calif. Another reader, schap329 of Richmond, Va., found a dominant applelike component on first opening the bottle, but noted an evolution over dinner as the wine warmed in the glass, like traveling “from the orchard to the ocean.” Jim M. in Madison, Wis., tried three different wines, likening one to “a seashell reduction,” noting citrus and “lots of minerals” in a second and “sea salt” in the third.

The influence of geology in the case of Chablis is so powerful that it may even overcome the characteristics of the chardonnay grape. Consider that Chablis, though it is classified as part of Burgundy, is in fact nearer to Sancerre than it is to the Côte de Beaune, where most other great white Burgundies come from. Parts of Sancerre and Chablis have more in common geologically than Chablis does with the Côte de Beaune, and, even though Sancerre is made with sauvignon blanc rather than chardonnay, good Sancerres can sometimes be mistaken for Chablis and vice versa.

Chablis is one of the most famous names in white wine, so famous that after Prohibition, big American wine producers appropriated the name for their white wines, a practice that continues today with the cheapest jug wines. Despite its fame, as Clive Coates points out in “The Wines of Burgundy,” the ravages of phylloxera, two world wars and severe midcentury frosts reduced Chablis in the 1950s to a scant fraction of its 19th-century production. It has made a welcome comeback since then, and the overall quality of Chablis has probably never been higher.

Yet, the issue of inconsistency dogs Chablis. Mostly, this occurs on the lower end. As with all of Burgundy, Chablis vineyards are rated hierarchically. At the bottom is petit Chablis. Then comes straight Chablis, premier cru and, at the top, grand cru. The historic core of Chablis encompasses the grand cru and premier cru areas. But a good deal of what is now called Chablis and petit Chablis is a result of an expansion of appellation boundaries since the 1950s.

Nowadays, grapes made into petit Chablis and Chablis may be planted in areas that may have little in common geologically with historic Chablis. Some producers are indifferent in their viticulture and winemaking, producing mass-market chardonnay rather than distinctive Chablis. Vintage is crucial as well. Climate change, which has reduced the danger of killer frosts, sometimes results in seasons too warm to produce wines with characteristic Chablis austerity. As is so often the case, consumers must take great care in selecting wines from conscientious producers.