I first heard about cod sperm, and how it's an edible delicacy for the "jet set," back in December. Socialite wrangler Gilt City threw an upper crust mingle fest at Benu. Chef Corey Lee decided to serve a liquified version of cod sperm in shot glasses as a passed appetizer. The well-to-dos knocked it back and liked it with reckless abandon (even though most of them didn't know what they were sipping). And the Chronicle's Beth Spotswoodwrote about the affair and her server's insistence that "it's like a thing. It's the male version of caviar."

Intrigued, I asked around. Hiro Sone of Ame confirms the coastal communities of Japan have forever appreciated cod sperm sacs -- otherwise known as shirako or milt. At Tokyo's Tsukiji Market, fisherman display raw cod fish with belly cut open so shoppers can see the size and color of the sacs before making a purchase. According to Brock Keeling, SFist editor and staunch cod semen supporter, it's "salty and tangy going down."

After this snippet of education, I jumped at the chance to sample the rare treat when it caught my eye on the specials board at Izakaya Sozai last month. As many izakaya chefs do, Ritsu Osuka serves it tempura-style with a simple garnish of shio salt. Our server likened the flavor to sweetbreads, but when I bit into one of the fluffy fried blobs on my plate, there was none of the density or fattiness I expected. The flavor was mild, almost sweet, with a touch of ocean flavor and a creamy, soft finish. It was delicious. Why aren't Americans clamoring for the stuff with the same fervor as the Japanese?

Chris Cosentino of Incanto says its a culture thing and I'd have to agree. In Japan it's a given that the whole animal will be consumed, so eating a sexual organ is no biggie. It's a highly seasonal commodity, with a peak that runs from January to March. The Japanese are so crazy about the stuff, they'll import it from Boston when necessary, using the sacs to enrich miso soup, fish cakes, even the soy sauce to accompany cod sashimi. In this world, we're mere characters in the Plato's cave of cod sperm understanding.

Sone has more luck with shirako at his wine country restaurant Terra, although he'll put it on the menu at Ame when it's in season. He prefers to serve it lightly poached with ponzu, but admits the agedashi fry method is more palatable to first timers. As a matter of fact, he's probably getting a pound in today from his local supplier. We may just be lucky enough to have a little extra cod sperm in SoMa this weekend! Can I get a little enthusiasm from the crowd please?

It ain't no thing at Incanto, where Cosentino has put cod milt in his head-to-tail dinner and featured in his "soft roes on toast" for quite some time. He also does "fisherman's breakfast," consisting of cod milt with a sunny side-up egg, capers, parsley and brown butter or he'll poach it and put it in ravioli. Incanto has made a name for itself pulling off obscure cuts of meat with panache. Instead of sugar coating their menu descriptions there's more of the "What? You don't dig cod sperm?" implication.

But perception issues are clearly an issue if Benu felt it better etiquette to cloud the truth for everyone's enjoyment at the Gilt City party. Izakaya Sozai defaults to telling people it's "like sweetbreads." If pressed they'll call it "a cod egg sac of some sort." According to Sone, the prevalence of uni and salmon roe at sushi bars has helped open people up to the cod sperm phenomenon, but we're nowhere near the outright adoration that might be more fitting of such a treasure. "It's still undercover here," says Sone. "Still hard to find."