Welcome to Savor the Science! In each Savor the Science, RENDER’s resident chemist, Claire Lower, will explore culinary questions through a scientific lens, perfecting recipes and demystifying techniques. Theories and reactions will be discussed and experiments will be performed; it’s like your high school chemistry class, only edible. Twice a month, Claire will take a scientific concept (such as the acid-base reactions in baking, macerating, or Maillard browning), explain it in a way that would make Bill Nye proud (hopefully), and then provide an edible experiment which allows you to demonstrate your new scientific food knowledge.
It’s science you can eat!
Mashed potatoes are one of those things that sound much simpler than they actually are. The instructions are practically in the name: mash the potatoes. What could be easier?
A lot of things, really.
Potatoes come in many different shapes, sizes, and colors. Can you mash the same potatoes you would use in a salad? What’s the difference between “waxy” and “mealy”? What the heck are new potatoes and can you buy old ones?
And perhaps the most pressing question: Is it just me or are do purple mashed potatoes look like something from the replicator on Star Trek: The Original Series?
The decisions continue past the choosing of the potato. Once you’ve picked one, you’re confronted with a whole new series of choices. You can mash your tubers using a stand mixer, a food mill, or a big wooden spoon but – for some reason – a food processor renders them gloppy and glue-like. If Friends has taught us anything, it’s that people have a lot of opinions on potatoes and how they should be prepared.
I can’t tell you how you’ll like your potatoes, but I can tell you how to predict their behavior, giving you the power to call the shots on the mashed potato-related issues in your home.
IT'S A TUBER—KNOW YOUR SPUD.
There are literally hundreds of different potato species (don’t’ worry, I’m not going to name them all) that are indigenous to the moist and cool areas in the Americas. They’re easy to grow, hard to kill, and one of the most widely consumed vegetables in the U.S.
The potato is a tuber that resides at the tip of the stem and swells to store starch and water. “New” potatoes are those little, thin-skinned guys you see that are sometimes referred to as “creamers.” They are essentially babies, dug up in the spring before they are fully grown, and are lower in starch than their mature counterparts. Their skins are delicate and flakey and their flesh is sweet and moist, making them perfect for salads and simpler cooking methods.
Because of their thin skins, a little more care must be taken when storing them. Don’t rinse them until just before cooking – that bit of dirt helps protect them from light, which will turn them green – and water can get trapped in the eyes and crevices, creating a breeding ground for mold. It’s best to use them within a few days of buying and keep them in a paper bag in the fridge until you’re ready for them.
Before mature potatoes are harvested, their vines are killed by cutting or drying and they are left in the soil for a few weeks while their skin toughens up. Once dug up, they can be stored in a cool (45-50 degrees Fahrenheit), dark environment for a few months, where enzymes will get to work on cell-membrane lipids to generate fatty, fruity, and flowery notes. Warmer temperatures encourage sprouting, and anything colder can alter their metabolism, resulting in the conversion of starch to sugar which can brown if exposed to high cooking temperatures (McGee 1984, 302).
SPEAKING OF STARCH
Have you ever cut up a bunch of potatoes only to turn around and notice that your knife is covered in a fine, white powder? That powder is potato starch, a carbohydrate stored in granules within the potato’s plant cells.
The powder that you see is “raw” starch in its semi-crystalline form, and it’s much harder for your digestive system to break down. When heated, the starch granules swell and separate and the potato becomes dry and fluffy–perfect for mashing.
Newer potatoes are sweeter because their sugars have not had time to convert to starch. This allows them to hold their shape better when cooking (due to a lack of swelling and separating), making them more suitable for gratins, potato salads, and boiling whole and serving with a little butter.
But this doesn’t necessarily mean that any mature potato is fit for mashing; some varieties (such as red or fingerling) are naturally lower in starch and are referred to as “waxy.” Does this mean you can’t mash them? Of course not. You can do whatever you want in the privacy of your own kitchen, but the mash you make with red potatoes (around 16-18%s starch) will never be as fluffy as the mash made with the super starchy, or "mealy,” Russet (around 22-23% starch) (Potter 2010, 196).
Yukon Golds (which have a starch content of around 20.8%) are also a good option, as they have a naturally buttery flavor, but this is all a matter of personal taste.
WHAT'S THE DEAL WITH THE GREEN STUFF?
You’ve probably heard that green potatoes are poisonous. This is true, but the molecules that are responsible for that green hue are not what ails you. All potatoes contain some amount of the toxic alkaloids (naturally occurring chemical compounds containing a lot of nitrogen) solanine and chaconine which give the potato that characteristic, slightly bitter flavor. Most varieties contain 1-15 milligrams of the two compounds per 100 grams of potato, but levels higher than that (according to the FDA the toxic dose is 20 to 25 mg ) can result in a burning throat, digestive problems, and possibly death.
Exposure to light can double or triple the normal levels of these alkaloids (Mcgee 1984, 302), making it best to store them in a dark environment. Light not only increases toxicity in potatoes, but can also turn them green. The green cast you see is not technically indicative of these toxins – the green stuff is actually chlorophyll – but it does indicate that the potatoes have been in more light than they should have. So, while there are truer indicator of solanine and chaconine (for instance, a strong bitter flavor), it’s still best to avoid – or at lease deeply peel – green potatoes.
WHAT HAPPENS WHEN YOU MASH IT?
Once your (decidedly un-green) potatoes are cooked and your starch granules have swelled, they are ready to be mashed. This can be accomplished by potato masher, potato ricer, big wooden spoon, stand mixer (at a low speed), or really any device strong enough to break up the flesh of the potato.
When you mash them with one of the above implements, you are breaking them into smaller particles but leaving those starch granules intact. This preserves the texture of the potatoes and prevents them from becoming glue-y. You can then lubricate the particles with the dairy of your choice, giving them a creamy mouthfeel and rich taste.
It might be tempting to speed things up by throwing them into a food processor, but the force from the blades will cause the swelled starch granules to break open, releasing the starch and allowing it to mix water, forming a gloppy paste. If you are one of those people who simply despises lumps in their mash, use a potato ricer; a food processor will eliminate all lumps, but it’s not worth the cell damage and resulting (terrible) texture.
Because I prefer experiments and pictures to words, I have prepared two batches of mashed potatoes: one with my stand mixer and another with my food processor. I’ll let the photos speak for themselves.
The potatoes prepared in the food processor certainly look smoother, but putting them in your mouth is less than pleasant. They are sticky, gluey, and reminiscent of boxed mashed potatoes.
Mashing with a spoon and whipping for a bit with my Kitchenaid left a few lumps, but the texture was fluffy and light. Besides, I add so much gorgonzola to mine they’re going to be a little lumpy anyway. Embrace the lumps, I say. That’s my life motto.
And because mashed potatoes are delicious, I will share with you my favorite recipe. Spoiler alert: I like mine well-lubricated.
Claire’s Somewhat Lumpy Steakhouse Mashed Potatoes
2 lbs. Russet potatoes, peeled, chopped, and boiled until fork tender (about 15-20 minutes).
3 oz. cultured butter
4.5 oz. blue cheese
0.5 cups of heavy cream
2 tablespoons of Worcestershire sauce
Drain the potatoes in a colander and transfer to a mixing bowl. Add butter and mash and stir with a big wooden spoon or potato masher until butter is completely melted and combined. Crumble blue cheese and stir in completely. Heat cream in microwave for about 40 seconds, pour in and stir until cream is absorbed. Add Worcestershire sauce and stir. Whip using the whisk attachment on your stand mixer until potatoes are fluffy and serve.
Jeff Potter. 2010. Cooking for Geeks. (Sebastopol: O’Reilly), 196
Harold McGee. 1984. On Food and Cooking: The Science and Lore of the Kitchen. (New York: Scribner), 302-303