You know those polygons of preternaturally bright color that you see as you fly into San Francisco? Ever wondered what toxic waste teems inside those flimsy bayside borders? I learned the answer. It’s salt. Saltwater, actually, in various concentrations. And various concentrations attract various algae and brine shrimp, which make the ponds the color of Day-Glo popsicles.

Cargill (maker of Diamond Crystal) owns them all, and the company recently invited a few people to tour their sea salt facility in the San Francisco Bay.

Some 250 million tons of salt are produced each year on the planet; approximately 40 percent comes from the US and China. Much of it is harvested via “solar salt production”—in other words, drying out saltwater in the sun and wind. Cargill harvests approximately 500,000 tons of salt from San Francisco Bay each year, or about .2 percent of global production.

Cargill’s ulterior motive was, no doubt, to show us the thousands of acres of reclaimed wetlands the company oversees, having given back (part sale, part donation, much thanks to Senator Dianne Feinstein) a big part of their salt-making land in the southern part of the bay. But that’s okay: The recovering wetlands are impressive.

And so’s the salt harvest. Here’s how it works: Saltwater comes in at Alameda Creek. (Sea salt is 3.5 percent saline; the bay is 2.5 percent.) San Francisco Bay is especially good for sea salt harvest because it’s flat, temperate, and windy. The brine gets pumped and streamed through sloughs and polygon ponds, and as it evaporates, the salts concentrate, and the nontasty salts—potassium chloride, magnesium chloride, for example—separate from our tasty friend sodium chloride. Eventually what’s left is simply salt—more of an ice rink than a pond, rock hard and bright as snow. Trucks come in to plow it and cart it away, just like on an icy highway.

From there it goes to the wash house, is screened and packaged, and becomes rock salt, table salt, kosher salt, and other salty products. The whole cycle takes five years. For more, check out my comrade Emma Chistensen’s photos at The Kitchn.

Image source: Flickr member Laurel Fan under Creative Commons

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