Q. Our church group made a potato and ham casserole with a cheese sauce. This consisted of cubed ham, sliced potatoes (raw), some milk and cheese. The casseroles were placed in aluminum baking pans, covered with foil and frozen (about 1 ½ to 2 weeks), then thawed in the refrigerator and baked. The potatoes turned dark (almost) black. Obviously, they were not able to be eaten. What did we do wrong?
A. So sorry to hear the plans for a casserole dinner were ruined. What an expensive result…
Potatoes turning black, good question, here is the short answer… raw potatoes can’t be frozen. There is an enzyme reaction that has to take place to keep the potatoes from turning black. In the future, you’ll need to cut the potatoes, placing them into water with a little lemon juice or white wine vinegar (something acidic) and then you need to blanch them by heating in water till mostly done. Then drain and layer your casserole as usual.
You hit upon the scientist’s discovery of how to do frozen French fries. Ray Dunlap of Simplot found that if he partially cooked the potatoes they could be air dried and frozen for frying later. Thus, McDonald’s switched over to the crispy shoestring potatoes they still use today.
Q. I would like to bake the potatoes for twice baked potatoes a day ahead of time since my oven will be in use the day of my dinner. After I have hollowed out the potatoes and prepared the stuffing, what is the best way to reheat the shell before returning the prepared potatoes to it? 
A. The Idaho Russet Burbank variety is typically harvested from mid-September to mid-October each year. It is a late maturing variety. Others such as the Russet Norkotah from Idaho grow to maturity earlier and are typically harvested in mid-August to mid-September. Idaho rules and regulations require that bagged or carton potatoes carry the variety designation right on the package or noted on a quick lock enclosure tag on bags sold in retail outlets such as grocery stores. Potatoes are harvested once a year, then stored for consumption throughout the year. So, in November you may see both varieties mentioned earlier being sold side by side. Our web site has a terrific educational piece, the Foodservice Toolkit, which can be viewed as a PDF by clicking on this link: 
