If you've ever had the 10-year-aged cheddar from a cheesemaker like Hook's in Wisconsin, you know that really old cheddar is a unique thing— nutty, brittle, almost translucent. But that cheddar is just a kid compared to some cheddar that will go on sale in Wisconsin in October. Ed Zahn, longtime cheesemaker at now-closed County Line Cheese in Oconto, retired in 1989 for the somewhat easier life of running a retail shop. When he closed that this year, he discovered some misplaced, unaccounted-for cheese in his cooler that had been aging there under proper storage conditions since the store had opened. The oldest— 28 years old, made when Ronald Reagan and Walter Mondale were the presidential candidates— has been certified as the oldest commercial cheddar ever sold in America. The 20-plus-year old cheddars will be available only at the Wisconsin Cheese Mart store in Milwaukee, beginning October 6.