New Meat Nutrient Hypothesis

Red meat goes through a process called "hanging" before it's butchered. As in they literally put the carcass up on a hook and wait.

"My opinion is that 7 days for pork is plenty"

"Beef benefits from being hung as a process called proteolysis [that] tenderizes the carcasses -  nowadays it is popular to hang to 21 or even 28 days."

https://www.accidentalsmallholder.net/forum/pigs/how-long-to-hang/

Why does grocery store meat go off so fast? Because it's already fermented. They butcher it at the last second. The bacterial action gives gives it a nice, rich taste. Poultry, by contrast, is often slaughtered at the factory (by a machine, incidentally). 

Red meat has longer generation times, which means they've been "scientifically" bred for fewer generations and are less debased than white meats. However, the bacterial action is quite possibly even more important. Bacteria always have a full set of vitamins and amino acids because they're the ultimate source of most of them, among other reasons. If your meat is deficient they'll go ahead and generate most of what's missing. 

Remember, eating empty calories will actually deplete your nutrients, because it costs nutrients to digest things. Junk food isn't just junk, it's effectively poison. It nearly goes without saying that grocery store food is often actively poisonous when it's not a deserted wasteland. Red meat is an exception, and if you try a heavily meat-based diet you'll notice right quick.

I now believe this is mainly due to fermentation.

Speaking of fermentation, it's illegal to ferment kefir enough to be genuine kefir. However, they put enough sugar in it (to make up for the weak taste) that you can casually finish fermenting it at home. I found out kefir is supposed to have a bit of a soda sparkle to it, by leaving a tub of it out for about three days. Just put it on top of the fridge instead of inside the fridge. However, if you leave it too long, it does go bad. 

I'ma risk poisoning myself and open it up to test. I'll try not to contaminate the batch by using a freshly-washed spoon, and I'm going to rely on the pre-existing culture to outcompete any interlopers. Maybe worst case I have to scrape off a fuzzy invader. 

Or maybe it goes horribly wrong. Wish me luck!

P.S. Salmonella is basically not a problem with fresh meat. Unless the animal was obviously already dying of it they won't have a big enough colony to hurt you. However, if you shut down the immune system via slaughter and then wait for a week or more, guess what happens.