Restaurant consultants Baum and Whiteman predict 2010 will be the year tongue, oxtail, tripe, and other offal go mainstream. The reason? Serving these off-cuts can lower food costs, cut down on wastefulness, and help ever-curious diners become more adventurous. To wit: Last Sunday evening, Opus Restaurant's chef-owner Michael Long hosted a specially crafted offal dinner for more than 50 members of the Denver Adventurous Eaters Club. The meal began with a Vietnamese pho, made with briny sea urchin, chewy tempura-tripe, and spicy chile-pepper noodles in an elegant, gingery broth. Next up was a more classic (and rich) French preparation of tender, pan-fried sweetbreads and mustard-roasted lamb kidney served with a Syrah-oxtail jus. Tip: Members of the Denver Adventurous Eaters Club will partake in a lutefisk meal at the Trollheim Lodge on Saturday, and Opus Restaurant will host more adventurous meals in the coming months. Check the restaurant's Web site (linked above) for details. Opus Restaurant, 2575 W. Main St., Littleton, 303-703-6787