College students and survivalists rejoice: Costco is selling a 27-pound tub of mac-and-cheese with a shelf life of two decades for $89.99.

Unfortunately it's not available in stores. ("A 27-pound bucket of macaroni and cheese?" said one employee over the phone. "No.") It's also intermittently out of stock on Costco.com. As of mid-afternoon on Friday, it's sold out.

If it remains that way, you can also find it for $149.99 on Amazon, although stock appears limited there, too.

The Chef's Banquet Macaroni & Cheese, listed under Emergency Kits & Supplies, offers 180 servings in separate pouches of elbow pasta and cheddar cheese sauce. That comes out to two servings per dollar.

For maximum longevity, Chef's Banquet recommends storing the tub in a "dry, cool environment." A doomsday bunker, for example, or a root cellar. You can put it next to your 7-pound bucket of Nutella and 40-pound bucket of honey.

The product's two-decade shelf life may freak you out. That is, after all, longer than many canned foods and grains last, according to the U.S. Department of Agriculture.

But "preservatives used in food are approved by the regulatory agencies," says Joseph G. Sebranek, a distinguished professor at Iowa State University who researches food safety.

While Sebranek isn't familiar with this exact product, he says that, if it's on the market, it's probably safe.

And, if you trust the reviewers on Costco's website, the mac-and-cheese is actually pretty good. "Very pleasantly surprised," wrote MimiO in a five-star post from three years ago. "You can't mess it up. Have purchased it again, and will continue to use it." Indeed, potentially for the next 17 years.

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