When cooked, potatoes are generally categorized taste-wise as floury or waxy. What determines that texture, is directly related to the amount of starch the potato contains.
A potato is about 75% water, 20% carbohydrate (starch), and 5% protein. The amount of starch in a potato can range from 16-22%, with a lower starch content meaning that the potato will be firm, and waxy in texture while those with a a higher content are drier and fluffier.
Each variety of potato (and there are hundreds!) has a varying degree of starch. So choosing the right potato for the right recipe makes all the difference in your dish being a success or a disappointment.
Starch determines the potatoes purpose
What would you prefer - mashed potatoes that are smooth and creamy, or lumpy? Potato salad with firm chunks of potatoes, or those that fall apart as soon as you try and spear them with your fork? Once you understand how a potatoes starch content affects it once it has been cooked, you will be able to choose the right potato variety for your recipe.
High-starch, low moisture (russet, Idaho) – Once cooked these potatoes are light and fluffy with a crumbly and mealy texture. Best for baking, mashing, and frying because all those starch molecules burst once cooked meaning they are readily available to absorb liquids (like adding butter and milk for mashed potatoes). But because of their ability to readily absorb water, when boiled these types of potatoes will be quite mushy and fall apart. So best not to use for dishes like potato salad where you want the potato to retain its shape. Another great use for this type of potato is when you want to thicken a soup. As the soup simmers, the small chunks of potatoes begin to break apart causing them to release their starch granules into the broth and thicken it. High-starch potatoes are perfect to make french fries - as the starch granules start to swell on their outsides once they begin cooking, moisture is pulled from their centers. Ending up with a crispy outside (which prevents the oil from being absorbed) and fluffy dry interior.
Medium-starch (yellow, fins, white, purple, Yukon Gold) – These potatoes can be used as an 'all-purpose' potato if you cannot eat high starch potatoes due to dietary restrictions, although they will still lose their shape a bit when boiled. If using them to make mashed potatoes, expect the overall texture to be more creamy than light and fluffy.
Low-starch, high moisture (red bliss, fingerlings) – Firm, waxy texture. The cells of these potatoes adhere to one another and swell, helping them retain their shape making them the best for boiling and dishes like scalloped potatoes. Because they won’t absorb liquid as easily, using them for mashed potatoes isn’t ideal since they won’t mash up as smoothly and will be quite dense in texture. Great for cold potato dishes like potato salad. These potatoes brown better than the other varieties due to their higher sugar content.
Are you boiling your potatoes correctly?
Most people bring the water to a boil then add in the peeled potatoes. Right? Wrong.
By placing the (peeled and quartered) potatoes in cold (and salted) water and bringing them to a boil, this allows the potatoes to uniformly cook at the same rate, because their interior temperature will increase at the same rate as their exterior. Preventing the potatoes exterior from getting overcooked and turning mushy. This boiling method gives the potatoes and overall better and consistent texture throughout.
For mashed potatoes, add flavorings in the proper order
To prevent mashed potatoes from getting a thick and gummy texture, after you have roughly mashed them (using a hand masher or ricer), do not add in any liquid (like milk or stock) until after you have thoroughly mixed in the melted butter/margarine into the potatoes first.
The fat (melted butter), quickly absorbs into the potatoes and coats all the potatoes' starch molecules. This creates a 'water-proof' barrier that prevents any liquid from coming into direct contact with the starch molecules - which is what causes the gummy texture.
Keep potatoes away from direct sunlight or they will develop a green color on their skin which is a toxic compound called solanine. If ingested it can cause cramping, headaches, diarrhea and fever. Although it doesn't contaminate the entire potato, so any green parts can simply be cut away.
Potatoes do come in bags with ventilation holes, however they should be removed from their plastic bags and stored in a bin or box that is located in a cool, dry, well-ventilated, dark space. This will prolong their shelf life and prevent premature rotting.
Never refrigerate potatoes as this starts to convert their starches into sugar, which will affect how they cook - and ultimately their texture.
Equivalents: 1 lb = 4 cups diced = 1 3/4 cups mashed