The bright, bulbous, red and yellow graffiti spattered over the cement wall is hard to make out. The word seems to start with an “H,” then an “E,” and an “R.” Could it really be … “Hermitage”? Yes, someone has sprayed the name of the great wine appellation from the northern Rhone Valley across the cinder blocks. That’s not all. That blazing orange scrawl: Petrus. And the long, blue tattoo half obscured by a stack of boxes: Gewurztraminer.

It’s not the usual subject of graffiti. Then again, it’s not the sort of interior design you expect as you approach the hallowed wine cellar of Daniel, the celebrated Upper East Side restaurant where chef Daniel Boulud’s culinary empire began. But when the French-born restaurateur learned that one of his pastry chefs, Jason Pitschke, moonlighted as a graffiti artist, he commissioned him to brighten up the stark, ugly, sub-basement walls leading to the cellar. Messrs. Boulud and Pitschke hatched a design in which the names of the great wine houses, appellations, and grapes were given the bubble-letter treatment.

It’s doubtful that graffiti is much to the artistic taste of Daniel’s sommeliers, Philip Marchal, 35, and Andre Compeyre, 36. Impeccably outfitted in finely tailored suits of blue and gray, they could pass as curators at the Met. Mr. Marchal, an Alsace native, rose to his position a year and a half ago after serving under the restaurant’s former sommelier, Jean Luc Le Dû, for several years. Mr. Compeyre, who was born in the Languedoc Roussilon region in southwest France, and previously oversaw the wine list at Alain Ducasse, was brought on board four months ago.

The duo serve as co-sommeliers — an unusual arrangement in the New York restaurant world — and look after the 1,600 varieties and 25,000 bottles on the heavily Gallic Daniel wine list. (The French to non-French ratio is about 60-40). The bulk of the collection is stored in a warehouse in Jersey City, where Bordeauxs from the 2000 vintage and the like bide their time on the slow journey to maturity. “I know nobody will touch them there and the temperature will be controlled,” Mr. Marchal, whose heavily accented English tumbles out of his mouth as quickly as Krylon out of a can, said. “We’re just waiting until it’s ready.”

Though Daniel’s East 65th Street address — the former Mayfair Hotel — was the home of Le Cirque between 1974 and 1996, Daniel’s wine cellar space had never served in that capacity before Mr. Boulud moved his eatery here in 1999. The architects and developers who were then converting the Mayfair into luxury condos didn’t even know the sub-basement space existed. Mr. Boulud alerted them to the hidden chamber; he was the executive chef at Le Cirque between 1986 and 1992, and has lived upstairs since Daniel opened, so he knew every corner of the building. After conferring with Mr. Boulud, the architects re-filed their plans with the city.

The New Jersey storage space notwithstanding, plenty of prized bottles reside in the compact cellar, some of the oldest and priciest in a waist-high rack just to the right of the room’s heavy metal door. “I keep them right near the office just to make sure they’re here,” Mr. Marchal, taking up a $7,800 bottle of 1961 Latour, said. “Then I’m sure every morning that my bottles are here.”

Mr. Boulud has a special relationship with the owner of Latour, Francois Pinault. He is a frequent guest at Daniel and a fan of the chef. Thus, diners with the wherewithal can choose from among the otherwise hard-to-find ’09, ’59, and ’70 Latour vintages. But, then, the list —which comes in two volumes, one for red and one for white, and runs 76 pages — is full of celebrated wines, including multiple vintages of Chevyl Blanc, Romanee-Conti, and Haut-Brion.

There are, and ever will be, Big Red fiends who are willing to max out the platinum card to uncork them. But Mr. Compeyre finds that many of his clients have discovered a new spirit of adventure in recent years.

“There are more and more people interested in being surprised,” he said, surprising this reporter by pouring out a glass of a floral Greek white from the island of Santorini. “It is part of the excitement of our positions as sommeliers. Maybe 20 years ago, the sommelier was the guy who was going to charge you $100 when you were willing to spend $50. We are now just somebody who is working with the selections on the wine list. Today, customers will say, ‘Usually I will have cabernet sauvignon. But I am having this for dinner. Can you find something to surprise me?’ You are trusting this person.” That there are nearly 100 bottles under $50 on the list aids this exploration into unknown terroir.

On Mr. Compeyre’s dark blue lapel, he wears a small pin: a silver cluster of grapes, discernable only if one leans in close. “It is discreet,” he said, “but maybe the customer will see it and think, maybe he’s the wine guy.”

Has Mr. Boulud ever suggested that he wear a tastevin, the traditional clunky chain and silver cup, which in olden days identified a sommelier? There is a short silence and both men bristle perceptibly.

“I never wore it because I never wanted to,” Mr. Marchal said firmly. “I don’t like it. I think it’s kind of …” Funny looking? “Yeah.” (It would also obscure his fabulously iridescent tie.)

“I did wear it for the first restaurant I worked at, outside of Toulouse in the southwest of France,” Mr. Compeyre said. He then cracked the driest of smiles. “I’m quite happy to have it in the house, looking at it, and have my son play with it. In the restaurant, it’s a little bit like having the cow with the bell, and you can hear us coming from one end of the dining room to the other.”