Prime Time

I used the directions for the recipe “Prime Rib with Horseradish Jus” (“The Art of the Roast,” Dec. 22) to cook a 7 3/4-pound rib roast. Following those directions, I attempted to cook the roast at 350 degrees for 1 1/2 hours or to 130 degrees. The roast did not get done until it cooked for about 3 1/2 hours, at which time it was medium-rare in the center. My 1962 “Good Housekeeping Cookbook” says this cut in this size would be done at 3 3/4 to 4 1/2 hours in a 325-degree oven.

--FELICITY A. HARPER, Oxnard

The timing of a roast is very difficult indeed--as evidenced by the wide spread in the cookbook you cited. When we tested the recipe in our Test Kitchen, it was done in the prescribed time. But the same cuts of meat, weighing roughly the same, will cook in different times, depending on the shape of the cut, the distribution of fat and bone and the meat’s initial temperature and the oven used.