As plant-based hamburgers go mainstream, one start-up is pushing for an alternative to the alternative.

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There's never been a better time to crave a hamburger without breaking your vegan diet. As the Beyond Burger (and sausage) hist store shelves and the Impossible Burger goes mainstream at White Castle, the hunger for—or, at least, the investment into—meatless alternatives that taste like meat is only growing. Of course, more traditional bean-based veggie burgers have always been and continue to be an alternative to beef, even at Shake Shack. And if red meat was the only concern, you could always opt for an alternative like turkey, chicken, or salmon. But what if you want an alternative alternative to the alternative? That is to say, a meaty, non-meat burger that's not trying to be beef?

San Francisco-based start-up Terramino Foods—a product of University of California-Berkeley's Plant-Based Seafood Collider program and founded by biologists (and students) Kimberlie Le and Joshua Nixon—has recently perfected a fish-free salmon burger which it claims mimics the texture and flavor of real salmon. The "salmon" is made from a commonly consumed fungus called koji, and algae. The fungus is grown in a liquid where it can form into strands which are then harvested to create the "flesh" of the salmon. The algae is there, in part, to provide the seafood flavor. The final product contains less fat than farm-raised salmon while providing the same protein and nutrition levels as the real thing. According to Fast Company, Terramino could have the product in restaurants by the end of the year and the company is also working on a salmon fillet.

Certainly, vegan fish is nothing new. Specialty stores and online retailers have been selling faux shrimp and other seafood to hungry meat-eschewing customers, while vegetarian and vegan restaurants will use starches, flours or vegetables in place of shellfish. (There are even vegan smoked salmon and vegetarian sushi.) The gap has always been believability when compared to the real thing—a gap which Terramino and its burger-making brethren are eager to convince you they've closed.

So why replace meat at all? All three plant-based burger companies in question cite sustainability, rather than animal cruelty, as the driving force behind their mission to get diners to try a meat-free option. Mass beef cattle production is often pointed to as a major culprit of the negative impact our diets have on the environment. Meanwhile, Terramino's website states that more than a third of the world's fisheries are overfished and that seafood farm practices are rarely sustainable and often involve pesticides, antibiotics, and other chemicals. With seafood being the most consumed protein on the planet, it's a big market for opportunity as well as impact.

But with sustainability and a move toward a meatless diet are the goals of such products, one question remains: Should we be replacing meat with "meat" at all, or learning to live without burgers in the long run? The trend, in the short term at least, seems to favor the former.