Kasu: the next 'it' ingredient?
When Tony Conte, chef at the Oval Room, took the duck out of the oven, he immediately suspected something was wrong. The 18-hour marinade had produced a crisp skin with a glossy sheen. But the color was almost black. What could have gone wrong? Then he tasted it. Delicious. Who cared what color the skin was?
Conte's secret, if temperamental, ingredient is sake kasu, or the lees that remain after sake fermentation. A popular umami booster in Japan, kasu is still mostly unknown in the United States. Sold in blocks, the soft, crumbly sake looks like a cross between tofu and puff pastry dough and has an enticing, yeasty, fruity aroma. Mixed into marinades, it adds an indescribable oomph to meat and fish. "There are no good words for it. It's not like anything you've tasted before," says Conte.
Traditionally, kasu was seasonal, available in winter after the sake had been made. According to Esake.com, producers take the white mixture of sake and solids that did not ferment into alcohol and press them into cakes. When done by machine – as is the case with the kind you find in the United States -- those cakes are tightly pressed square pancakes. If made by hand, it will have a chunkier, crumbly consistency.
In classic Japanese cuisine, kasu is used to make soups, much like miso, and as a marinade for fish. Conte, blissfully ignorant of the history and therefore freed from expectation, immediately thought the flavor would work well with duck. He crumbles the kasu and blends it in a food processor with light soy, honey and thyme until it resembles a thick paste. He does not rub the marinade on the duck; it's too acidic and might "burn" it, he says. Instead, he puts a layer of marinade in the bottom of a pan, then a layer of cheesecloth, the duck, another layer of cheesecloth and, finally, more marinade. After marinating, the duck is roasted until the skin is very dark; any less and the flavor won't be as dazzling. It is served with duck confit "tater tots," farro, glazed turnips and pickled cherries ($27).
Conte is not the first to try to evangelize kasu. In 1998, Gourmet magazine ran a recipe for a kasu-marinated Chilean sea bass (before that was a politically incorrect ingredient). The recipe got raves, with one exception. Most testers couldn't find kasu anywhere. It's easy to understand why the magazine never employed it again.
Now, kasu has a second chance. It is available at Japanese grocery stores and some Asian markets. And its potential uses are huge. This fall, Conte plans to try a similar marinade on butternut squash. But it would be equally good with wild mushrooms or pork. "With a big piece of meat, I'd make slits and push the marinade in, then cook it really slowly. I need to write that one down and remember it," Conte said.
Kasu is available at Hinata Sushi and Grocery, 4947 Saint Elmo Ave., Bethesda, 301-656-1009. A 10.5-ounce package is $4.15.
-- Jane Black
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