Which Potato to use for which purpose?
On Friday my wife and I went to a new bistro in town to check it out. Generally, the meal was good, but there was one notable disappointment. For the starch with my main course, I ordered Potatoes Dauphinoise, a dish similar to scalloped potatoes topped with melted cheese. In this case, the potatoes were cut into fairly large chunks, maybe about an inch (2.5 cm) to a side. The insides were dry and grainy. The mouthfeel was very unpleasant. The reason was likely because the potatoes used were a high-starch variety, maybe Russets.
Potatoes come in essentially four kinds -- high-starch varieties like Russets, waxy ones like reds, in-betweeners like Yukon Golds, and new potatoes, which are small young potatoes of any variety with thin, underdeveloped skins.
High-starch potatoes are excellent for baking, where the starch swells with moisture from the potato, creating a flaky interior that absorbs the typical condiments like butter and sour cream. They also make really good fries, as the starch on the surface crisps and absorbs moisture from the interior, making a fry that stays crunchy and firm.
Red or other waxy potatoes have significantly less starch, which makes them well suited for boiled potatoes, and for use in potato salads or potato cakes.
In between high-starch and waxy potatoes are ones like Yukon Gold which work well in many applications such as making pan-fries and potato salads. In making pan-fries, I follow the method suggested by Cook's Illustrated and boil the potatoes for about seven minutes before draining and frying them. Without this step, you sometimes find that the outside is over-cooked while the interior is still too firm.
For mashed potatoes, recommendations vary. Some books suggest using Russets, while others say to use a waxy variety. Either works well, although the higher starch potatoes may have a bit of an edge. Personally, I prefer Yukon Golds, when I can find them. Unfortunately, they fall apart when over-cooked, so take care cooking them.
Because new potatoes are picked before they have matured, the sugars in them have not completely converted to starch, which makes them slightly sweet. They cook more like waxy varieties, so they are good for boiling or in salads. A favorite method is to boil them whole, in their skins, drain them, lightly crush them to break them open and then stir in salt, pepper, lots of butter and whatever fresh herb is on hand.
Back to the Potatoes Dauphinoise. High-starch potatoes might have worked, if they had been cut into thin slices, maybe 1/8 inch (3 mm), so that the starch could be released to thicken the sauce. At the same time, the interior would have absorbed some of the moisture and fat which would have made them softer and creamier. Waxy potatoes can also be used for this, or dishes like Potatoes au Gratin or Scalloped Potatoes. If the cook wished to use large pieces, as in the dish that was served, a waxy potato would likely have performed better.
As for the bistro, I sincerely hope it works out, as we can always use adventurous new restaurants. However, along the way they are going to have to pay a bit more attention to the details of what makes great food and a great dining experience. I wish them well.
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