We have some organic yellow potatoes that will not brown or crisp while frying, they just turn burnt-black at the edges and get mushy (whether we've precooked them or not). The raw potatoes are firm but not hard, very few spots, and of course we only use unblemished flesh. Please help!
This sure sounds a lot like potatoes that have been stored too long, in too cold of an environment before cooking. When potatoes are held below 41°F for too long a period, the starches convert to sugar and it changes the cooking chemistry. Instead of a nice caramelization, potatoes will often cook up overly-sweet and have unappealing, odd shades of black or gray.
Here’s a quick test to determine if your potatoes have been stored too cold at some point along the distribution chain, and how to resolve it, if so: