I've read a variety of articles on blanching potatoes. I've seen recommendations of seven to ten minutes time. That is not blanching, it is cooking.
The purpose of blanching is to stop the normal enzyme changes that continue to ripen and eventually rot a food. This is done by heating the item in boiling water, then plunging them into cold water to stop the cooking process.
Here is how I do potatoes:
- Peeling the potatoes is an option, do it or not as you choose.
- Slice the potatoes and immediately put them into a bowl of water to keep them from turning brown. You want fairly even thickness, so if you have quite a few to do, use your mandolin slicer. I used to snip off the ends of my fingertips until I learned to stop short. Take those little rounded ends and dice them separately later. If you like, julienne potato strips or even shred them for home fries.
- Have a very large pot of boiling (not just hot, but rolling boil) water ready. Place a few potatoes at a time in the water. Don't put so many in that the boiling stops.
- Set your kitchen timer for 3 minutes from the time the boil resumes.
- When the bell dings, remove the potatoes from the water and plunge them into a waiting pot of cold water, then drain in the colander. If you are only doing a few potatoes you might want to go ahead and pour them out into a colander. But if you have several batches to blanche, keep the same hot water. It saves time.
- When the potatoes are cool and drained (use your salad spinner for shredded or diced potatoes) put them on the racks and dehydrate on low.