The subject came up at a dinner not long ago: It was bottle variation.

This is a bit of "winespeak" for the fact that two bottles of wine with identical labels could very well taste different. This happens more often than anyone wants to admit, especially the wineries.

Not long ago, I got a call from an old friend who had experienced this problem with a bottle from a case of wine he owned and thus knew well. The variation could have been caused by a number of things, from how it's handled at the winery to how we perceive it under different conditions.

One problem can be in the glassware. Was the glass washed in a solution that contained chlorine? Was it towel-dried by a towel that had been laundered with fabric softener? All of this could affect the aroma you get from a wine.

One of the greatest lessons of my life in wine was when an older, wiser friend, a longtime wine lover, told me, "There are no great wines, only great bottles of wine."

His point was that every bottle of wine, even a reputedly great wine, can be its own little chamber of horrors, and though it's rare, on occasion, a single bottle of an otherwise great wine can go bad, even if the other 11 bottles in the case are fine.

Of course, bottles from different cases, stored in different locations, may be widely different, especially over time. Two otherwise identical bottles of wine may be different because of how they were bottled.

Assume a winery is making 30,000 cases of a wine, which is stored in three different 10,000-gallon tanks. The best way to bottle it is to blend all three tanks into one 30,000-gallon tank, stir, and bottle. This master blend makes 360,000 bottles that all should taste about the same.

But if the winery has no 30,000-gallon tank to make that master blend, it may simply bottle the tanks one by one, and any difference between the various tanks may show up in the bottle.

With wines made in larger amounts, such as 100,000 cases, you can expect variation from one lot to the next. To minimize the possibility of getting radically different wines, buy in case lots, not a bottle here and a bottle next month somewhere else.

Also, winemakers know that wine is a living product. Wines that are not filtered have an especially high number of active elements. Some of the chemical changes that occur in a bottle actually make a wine taste better so you hear the phrase, "The wine needs time."

The most mystical thing is where great care is used in making the wine and one bottle from a case of 12 turns up to be different. A possible reason is the closure. Cork is less reliable than, say, screw caps.

Perhaps the biggest reason a wine can taste different is in us.

One night, you're in a great mood. You just got a raise, your kid came home with A's on a report card, and your accountant says you owe no taxes. You taste a wine, and it's wonderful. This wine, you remember.

Then there are other days: A slight cold or headache annoys you, you've got a beef with your boss, or you're irritated by a flat tire or someone trying to cash a check ahead of you in the checkout line.

The same wine doesn't taste quite right.

The late author H. Warner Allen said it best: "The wines that one remembers best are not necessarily the finest that one has tasted; the highest quality may fail to delight so much as some far more humble beverage drunk in more favourable surroundings."

Wine of the Week: 2005 Shenandoah Vineyards Sauvignon Blanc, California ($11) -- For those who do not like the grassy style of sauvignon blanc, this wine is a treat with melon-y, fig-like aroma and a nice crispness to work with grilled seafood.

Dan Berger resides in Sonoma County, Calif. Berger publishes a weekly newsletter on wine and can be reached at danberger@VintageExperiences.com.