Chorizo is the protein to watch at Chipotle Mexican Grill (NYSE: CMG).

A test of the Spanish sausage has played out so well in its test market in Manhattan that chorizo is being added to the menu through most of its New York City eateries. Chipotle's home turf of Denver is next in line to begin offering the sausage made of naturally raised chicken and pork.

Investors can usually ignore new additions at publicly traded chains, but this is Chipotle. The bare-boned menu makes any addition newsworthy, and the chain hasn't added a new protein to the menu in years.

The test markets are replacing grooved griddles with flat planchas, making chorizo -- and potentially other meaty additions -- possible.

Fans will argue that Chipotle doesn't need to fix what isn't broken. Shares hit an all-time high yesterday, as explosive unit-level comps continue to drive top-line surges and better-than-expected profitability.

The chain's appeal is in a limited menu that it can turn over quickly, giving the hungry relief in knowing that the line snaking through the store will be fed quickly.

There are off-menu items. Customer heads turn whenever I order a carnitas quesadilla -- or even a kid's meal -- but the employees never flinch. A test to expand into soup and value meals two years ago hasn't ladled with the masses. If folks want more than a few proteins served in a limited number of ways, they can always go to rival Jack in the Box's (Nasdaq: JACK) Qdoba for Mexican Gumbo or trade down to Yum! Brands' (NYSE: YUM) Taco Bell, where pocket change goes a long way.

If chorizo takes off, it won't complicate the menu, as it's a protein that can slide right into every bowl, burrito, taco, or salad that's already available. Turn heads with that chorizo quesadilla order the next time you're in New York City.

In the grander scheme of things, adding chorizo won't be the same kind of long-term needle mover that this summer's debut of sister concept ShopHouse will be, but it should increase traffic as variety seekers check out the new flavor combinations that are available.

What do you think of chorizo as the next Chipotle protein? Share your thoughts in the comment box below.

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