Which innovative food product is credited with creating the 'better burger' revolution that forced major fast food chains to improve their quality standards?

In the competitive food industry, product innovation can make or break a brand's success. Some culinary innovations fundamentally change consumer expectations and industry standards. This trivia question tests your knowledge about a groundbreaking food product innovation that transformed how we think about fast food and created an entirely new market segment. Do you know which revolutionary food product innovation caused its competitors to completely rethink their strategies?

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Shake Shack's custom-blend patty developed with butcher Pat LaFrieda in 2004
McDonald's introduction of the Quarter Pounder in 1972
Burger King's flame-grilled Whopper launched in 1957
White Castle's invention of the slider burger in 1921