Buttered Peas

And a primer on how (and why) to sort peas.

Peas by macoto_, on Flickr

Of all the vegetables you might encounter in the grocery aisle, perhaps only the Brussels sprouts are less understood by the common shopper. Peas are fantastic culinary and caloric investments—low in calories, high in phytonutrients, and if you know how to sort them, they’re delicious.

The short version is this: if you put shelled raw peas in water (or, ideally, a brine solution), the sweet ones will float and the starchy ones will sink. The sweet ones can be eaten on their own; the starchy ones tend to be better received in soup or in Indian cuisine—I love a good paratha with big, starchy peas.

If you don’t sort the peas, there’s no easy way to tell which are starchy and which are sweet—both kinds will show up in each pod and the flavor will be muted and muddled.

So why does this work? It works because sugar attracts water.

Okay, perhaps a little more explanation is required.

Peas are seeds, and a major goal of any seed is to store enough energy for a plant to grow until it emerges and can generate energy from photosynthesis. In the case of peas, that energy starts out as glucose, a form of sugar; as the pea matures, the glucose forms long chain molecules—or starch.

We learned all about starch in the post for mochi, remember?

Meatballs, Peas, Cauliflower Gratin, Fresh Apple & Milk by DC Central Kitchen, on Flickr. Notice the wrinkled texture on the peas, telling us they’re sweet, but the texture isn’t ideal, either from freezing or overcooking.

Now, ounce for ounce, the density of glucose is a tiny bit higher than the density of starch—but because the glucose attracts and retains water in the pea, the overall density of the sweeter peas is lower than the density of the starchier peas.

In factories, they sort peas with a brine system, labeling peas that float in 68 deg F. brine with a specific gravity of 1.04 g/cm³ as “fancy” and those that float in a brine of 1.17 g/cm³ specific gravity as “standard.” And if you’ve got the equipment to measure these things, well, you can go right ahead and do the same.

For the rest of us, a fresh egg will float in room temperature salt water when it reaches a density of around 1.08 g/cm³. So if you fill your vessel with water, then add an egg, and then salt the water and stir until the egg floats, you’ll be somewhere around 1.08 g/cm³, which should sort your peas quite nicely.

One last tidbit: because the sweeter peas have a higher water content, cooking them for too long (or freezing or drying, for that matter) will cook off more of the water, and the result will be a wrinkled skin. So when you see a plate full of wrinkled peas on the table, take comfort in knowing that at least they’re flavorful.

From the box of A.D. from Lutz, Florida, by way of Pennsylvania in the 1940s, and originating in Ohio in the 1920s.