About 100 fun loving wine enthusiasts each brought a 375ml bottle of their favorite wine to the annual Half-Bottle Party June 6, an unofficial — very unofficial — kickoff for the big auction week.

The event had its start six years ago when Scott Tracy, sommelier at La Toque in Rutherford, and  friends were chatting about the traditional magnum party that Wine Spectator hosts for its advertisers and VIPs on the Wednesday before Auction Napa Valley. All guests are asked to bring a magnum of their favorite wine.

 Tracy made an offhand comment that a party with half-bottles might also be appropriate. But there would have to be some changes.

Instead of holding it at an elegant restaurant, he’d do it at Taylor’s Automatic Refresher. And instead of a hosted sumptuous dinner, people could buy their own hamburger or cheeseburger or whatever they wanted.

The idea caught on and became exactly what Tracy wanted — an informal gathering where people came wearing jeans or shorts, some ate, some didn’t, but everyone had a great time.

There were wines of all colors — red, white, pink and sparkling. All who attended are in the wine business, so the assortment of small bottles on the table represented some of the finest that Napa Valley has to offer.

Tracy doesn’t send out formal invitations, because most attendees are regulars who put the date on their calendars well ahead of time. But for newcomers, he sends an e-mail reminder that contains some basic information to answer questions that are usually raised by the uninitiated

Q. Why are you having a half bottle party?

A. Because the idea of it makes people laugh. I have always enjoyed laughter. I have enjoyed hamburgers, wine and people as well. Shall we picnic?

Q. My winery doesn’t make 375mls. What should I do?

A. It is a half bottle party. Open a 750ml. Drink half of it and bring the other half.

Q. Should I stay at the half bottle party until the magnum party begins?

A. Perhaps, perhaps not. Again no rules. Proper etiquette would call for a 750ml party as an intermezzo. However that may not apply to everyone’s situation. I know some of you have to go to work, as I do.

Most people stick to the “rules” — almost all the bottles were 375s, and only a few 750s were seen, but no magnums. Those came later in the evening.

It’s unofficially called the BYOHB — Bring Your Own Half-Bottle — party, but over the years people have come up with their own descriptions of the event.

One regular attendee called it the “Bring Your Own Baby Bottle Party,” while another said it was the “Doo-Dah Parade with attitude," referring to the annual spoof of the Tournament of Roses Parade which has become a somewhat famous tradition.

The folks at Taylor’s know the routine by now — nearby was a large blue recycling container for the empty bottles. And there were a lot of them.