Mealy potatoes

Floury potatoes — also called mealy potatoes,

Starchy potatoes or baking potatoes — versus waxy potatoes — sometimes called creamy potatoes or boiling potatoes.

You want to know what makes these

Different? well, look inside.

Not in here. Here. This is a floury potato when raw. These are the individual cells. Those are the cell walls there and inside you see the individual starch granules. Each granule contains millions of starch molecules and each molecule contains like thousands of individual sugars, glucose units. Now here is that same potato, floury potato, when cooked.

You can still see the individual cell walls. They're a little hard to see, but there they are. And inside each of the cells is this kind of spongy mass. It's totally filled up with a spongy mass of gelatinized starch granules — granules that have absorbed a lot of hot water and they've exploded and they've totally filled up the cells. And then over here is that same floury potato mashed after it was cooked. And you can see that it kind of looks about the same. You can still see the cell walls, the integrity of the structure is basically still there. Compare those to a waxy potato.

Here are some waxy potatoes when raw. Look pretty similar to the floury ones, but check them out after they are cooked. The cells are not engorged with gelatinized starch. There's tons of empty space in here, and it's actually not empty — it's filled with cytoplasm, you know, water with a bunch of dissolved stuff in it, including sugar. Waxy potatoes have more sugar, and then here's that same waxy potato mashed. It is a mess. Everything's all busted up. These microscopic photos are from a 1994 paper out of Iowa State University, it's an oldie but a goodie, and having seen these photos, I think I finally now understand.

Both extremes of potato are great. Both can be used to make just about any potato dish that you could think of. The differences aren't that big, but there are real differences that make some of them better for some things than others. I usually call these floury potatoes because I feel like mealy is an unflattering description. These have more starch. They're usually 20 to 22% starch by weight. Waxy potatoes have less starch. They're generally 16 to 18% starch and the mass they lack in starch is instead mostly water.

They're less starchy, more watery. You can see and feel the difference here. Here I've baked both types until soft.

Inside, the mealy potato looks kind of

Dry and powdery, granular.

Its higher starch content absorbed basically all the water that was in the potato and there was proportionally less water in there to begin with. When I taste it, it tastes dry, which is maybe bad without butter, but it's also fluffy, which is good. The waxy potato cuts much smoother. It doesn't break apart in the same way and when I taste it, it tastes smooth and creamy, even without any dairy.

The reasons for this are probably multiple. One is that these cells in cooked waxy potatoes are not fully engorged with gelatinized starch like they are up here in the floury potato. The authors of this paper speculate that when you mash these microscopic cells around in your mouth, they burst, spilling their cytoplasm out and giving you that moist mouthfeel. The same process also likely happens when you make mashed potatoes with waxy potatoes. Mashing bursts the cells, water and starch pours out and they interact with each other to make a paste that a lot of people find unpleasant in mash. What waxy potatoes are really good for is boiling — putting them in a stew, any place where you don't want them to fall apart. People say they hold their shape better, which I think might just be a different way of saying they cook slower, which is definitely true. Floury potatoes cook faster.

Let's cut some waxy and floury potatoes into similarly sized chunks and boil them together. The mealy potatoes go fork-tender several minutes ahead of the waxy ones. Based on my reading of the research literature, scientists aren't totally sure why this happens. I mean, I could probably try to figure it out myself if I'd studied in college anything remotely close to what I do for a living now. Don't make the same mistake that I did — study something that will actually help you at work.

Anyway, floury potatoes soften faster than the waxy ones when they cook. The reasons are probably multifactorial.

The extra starch in the floury potato swells up bigger and that maybe stresses the internal structure of the potato — all the cells are kind of exploding away from each other. Yes, floury potatoes have more starch, but it's also a different composition of starch. The waxy potatoes are almost entirely amylopectin, which is the big branched chain of glucose that makes up a starch. With the floury potatoes, they're still mostly amylopectin, but they have also a fair bit of amylose, which is the long chains of glucose, that kind of starch. They're still mostly amylopectin, but there is a little bit of amylose in here as well and that does change things.

The presence of amylose may also accelerate

The cooking of mealy potatoes.

Amylose requires a higher temperature to gelatinize

With the water, but a lower temperature to solubilize, which is what happens next.

They break away from the granule and everything starts to fall apart.

And there are other components of potatoes that might explain why mealy potatoes cook faster. There's these studies out of the Netherlands where they looked at pectic substances that dissolve into the water when potatoes are boiled. Pectins help hold the whole potato together. The Dutch found that different amounts and different types of pectin dissolve out of mealy potatoes versus floury potatoes, so that could be relevant too. But there's another big and highly relevant difference between these two: Waxy potatoes have more water, and that makes them bad for frying. You can see it if I fry these parboiled potatoes in a little bit of oil. They brown at comparable rates. Maybe the waxy one browns a little faster owing to its higher sugar content, but you can plainly see the mealy one is cooking faster internally.

Look at the skin separating there. Water slows down cooking, and the waxy potato has more water. To get a waxy potato soft and fluffy and dry on the inside, we would have to fry it for longer, by which point to the outside would probably be burned. This is why french fries made with waxy potatoes are usually either overdone on the outside or they're underdone on the inside — they're wet on the inside, soggy. In the case of french fries, yeah, definitely, floury potatoes are what you want. But are floury potatoes better for mash? Some people say they are. They certainly soften up faster in the boiling water. There's reason to believe floury potatoes may integrate better with the butter too, because floury potatoes have more amylose and amylose forms bonds with lipids, complexes.

But I don't think I like the mealy texture, that granular texture the mash has on the tongue. This is where mealy potatoes get their name, but what actually is that granularity that we perceive on our tongue? Well, again, this awesome old paper from Iowa may show us the difference. This is the cooked mealy potato, it's a russet. The rest of these are cooked waxier potatoes and look at the lamella — that is the membrane between these two cells that kind of connects them together. It's the adjoining membrane between these two cells. The lamella here in the russet, the mealy potato, this is thicker and way more solid and what you can't see from the picture is that it's also more polarized. The cells are more polarized, electrically charged. The authors here attribute this to a higher concentration of calcium and magnesium ions in mealy potatoes.

The result is cells that are more likely to stick to each other, so while the whole potato seems to soften faster, the individual cells on a microscopic level are actually more solid, less likely to burst and spill their starch out and they also clump up with each other, maybe because of that charge. You can plainly see that clumping, even with this very weak microscope. Super starchy, fully engorged cells clumping together. That is probably the grain that you feel in your mouth. That is the meal. And not everybody dislikes it. There's another word that we have to describe big grains of something that are all kind of separate and not bound together by external water. What is it? Fluffy.

That's what the word fluffy means. Fluffy mash — people like it. The alternative is creamy mash produced from waxy potatoes. However, such mash does tend to go gluey for reasons previously discussed. The cells burst, starch and water fall out. You can, of course, get the best of both worlds by combining waxy and mealy potatoes in a single mash and that is exactly what I usually do. But I want to emphasize that a potato is just a potato. The differences between them really aren't that big. You can make good food with either one, so just cook whichever kind of potato you have...