This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
The potato is in such universal use, and is so highly nutritious, that above all other vegetables it would seem that it should be cooked in perfection. However, it may be in reality that no other vegetable is so carelessly cooked. The proper cooking of the potato has much to do with its nutritive value. It is a starchy food; the microscopic starch grains are intermingled with the watery juice, which contains the albumen, gelatine, minerals, sugar, and acids. All of these elements are highly valuable as food or stimulants, but by careless and unscientific methods in preparing and cooking they may be partially lost and wasted. How often do we hear epicures criticising our best hotel cooking, remarking the impossibility of being served with mashed potatoes of a good quality? Where food must be prepared in such large quantities the potatoes are pared and soaked in water for from twelve to eighteen hours before being boiled, thus losing a high percentage of the agreeable flavors, the nutritious starch and albumen and valuable mineral matter.
In preparing potatoes for cooking, by clumsy, awkward paring large quantities of the edible portion are wasted, one fifth on the average and as high as one fourth, when by careful measurement the crude fibre or true skin of the potato is less than one half of 1 per cent. of the whole. When potatoes are pared and soaked in water and then boiled the loss has been found to be as high as 7 per cent. of the food value, the albumen and mineral matter being the elements most largely lost. "The different methods of cooking potatoes are baking, boiling, steaming, and frying. Each of these methods may be so conducted as to retain practically all of the food material. When potatoes are cooked in the skins they lose nothing of the food value, but a slight loss of water is noted. When fried there is no loss of nutrients and the toasted or browned starch flavor is relished by many. Baked potatoes have been found by scientific experiment to be more quickly digested than those cooked in other ways, but it seems that in healthy individuals the time of digestion of food is not material so it is normally digested. A potato cooked in the skin, either baked, boiled or steamed, then peeled and mashed and seasoned with plain milk, has a richness of flavor, from the conserving of the elements of flavor, that no amount of high-priced artificial seasoning such as butter and cream can give. This does not argue against the use of cream and butter, but only calls attention to the fine, smooth consistency and good flavor that can be secured by conserving the cortical layer instead of paring it away. Chemical analysis has shown that as much albumen, the flesh-forming food, is thrown away or needlessly wasted in paring fifty pounds of potatoes as is contained in a pound of sirloin steak; besides this loss of nitrogenous food, that of the carbohydrates or starch is still more.
It is evident from all tests that if it is desired to cook potatoes with as little loss of flavor and food material as possible, they must be cooked with the skins on."
The following formulas for cooking potatoes are given as examples of methods by which all of the nutrients are conserved: