We need some help identifying a problem with the potatoes turning grey to black in color after cooking.  These are potatoes that are cubed and cooked in a combi steamer open pan during the cooking process.

A few variables:

1. Fresh whole potatoes are stored in a walk-in cooler at approximately 42°F
2. Potatoes are peeled in a commercial potato drum type peeler
3. They are cooked uncovered in standard hotel-type deep metal casserole pan

The grey to black coloring always occurs after cooking.  Sometimes the potatoes are prepped the day before cooking and held in a large plastic container with water and ascorbic acid added (lemon juice), but do not discolor prior to cooking.

I think it might be the drum peeler. Sometimes the bruising from tumbling in the peeler will not show up until cooked. This typically does not go through the whole potato, just the outer edges. Otherwise, I’m at a loss… Why not try hand peeling part of an order and putting the rest in the drum peeler to see if there is a difference.  Also, check the temperature of the potatoes as you may want to store them near the plastic strips at the entrance to the walk-in versus back and up high where no air is circulating. Dropping a carton 2-3 feet stresses the potatoes too, causing bruising.