Wonkblog

(AP Photo/Darren Calabrese)
The last time I ate a hamburger, the meat didn't taste as good.
That's because rattling around in my head was a fact that should have been obvious but hadn't dawned on me until recently: that meat patties aren't just made from the muscle tissue of a single animal, but from the fibers of as many as a hundred cows, or even more. We mix different kinds of cow tissue like one combines colors on a palette, potentially putting animals that once grazed next to each other into tightly packed beef discs.
It shouldn't matter how many cows go into a burger, but the number is a vivid and maybe even repulsive reminder that eating meat exposes us to a process where animals are slaughtered and mixed together for our eating pleasure. And while that may not change anyone's opinion about the morality of it all—it hasn't changed mine-—it still exposes us to a lingering pang of doubt about whether any of it is ethical.
"If you have a negative reaction to it, it’s probably because it makes you realize how much of an industrialized process animal production is," said Peter Singer, a professor of bioethics at Princeton University, and acclaimed moral philosopher. "You might still have this ideal that there’s a farmer with cows, and every now and again he has to kill one. If that's the case, you might not have a good grasp of how modern meat production works."
But the thing is that I do. My job is to think about the food industry, which means that I think about meat production ad nauseam. And that makes my reaction all the more telling. 
Hamburgers are the ultimate embodiment of modern day meat production. They are both one of the most ubiquitous forms of processed meat—they're on menus practically everywhere—and one of the least considered. Unlike a cut of steak, which necessarily come from the meat of a single cow, hamburgers are almost always a mishmash of many animals. The ground beef we buy at the supermarket is made of an unknown collection of muscle tissues. 
I tried to figure out how many cows are in a single hamburger. And it was really hard.
It is possible to eat a hamburger made from the meat of a single cow. Restaurants that grind their beef in house, mixing the cuts of only one animal at once, serve them. Those who raise their own cattle, and then slaughter them for food, can have them too. But the single cow burger is a rarity.
Last year, McDonald's confirmed that its beef patties can contain the meat of more than 100 different cows. But it isn't just the world's largest purveyor of hamburgers that has trouble keeping track of the animals in its meat.