Potatoes are either high, medium or low in starch, and different starches work better for different cooking methods. To figure out the starch content, simply cut through a raw potato with a knife. High starch potatoes leave a creamy white residue on the blade. The less residue the less starch.
Idaho & Russet Potatoes
Also known as "baker's potatoes", these potatoes are high in starch & low in moisture. The higher the starch content the more granular & dry a potato will be after it is cooked, making these potatoes more desirable for frying as they are less likely to splatter or absorb grease. As with all potatoes, the starch content will increase as the potato ages.
All-purpose or Chef's Potatoes
These potatoes have a relatively balanced amount of starch and moisture. They're usually found in salads, scalloped or other casserole style potato dishes, and soups. All-purpose potatoes tend to hold their shape after they are cooked.
This term applies to any variety of potato that is harvested when it is small and less than 2 inches in diameter. The skin of a new potato is tender and does not need to be removed prior to cooking or eating. The starch content in these potatoes is low and their water and sugar content is high. Their naturally sweet, fresh flavour is most enhanced when they are boiled or steamed.