It's been a hard recession for Burger King, and now execs at the world's No. 2 burger chain have sold the company to a private equity firm for $4 billion. Investors seemed ready for the change — BK's stock rose 15 percent on the news Wednesday, closing at its highest price since BK went public in 2006. Meanwhile, Burger King's biggest rival, McDonald's, has been enjoying stock-market favor. Where did BK go wrong, and is this deal a good idea? (Watch a Fox Business report about the sale.) A concise guide:

Why is McDonald's doing so much better than BK?
Analysts point to several reasons why McDonald's shares rose 17 percent over the past year while Burger King's dropped 13 percent. For one, it's a bad time to target young men and minorities, demographics that have been crucial to BK's bottom line and have been hit particularly hard by the recession. McDonald's has been doing a better job of attracting a broader clientele, offering "relatively healthy salads and decent coffee," says The Economist.

Why did Burger King's owners want to sell?
It's a good time to take a tidy profit. Three private equity firms — TPG Capital, Bain Capital, and Goldman Sachs — bought Burger King in 2002 from alcohol giant Diageo with $210 million cash down, then sold all but 32 percent in a 2006 public offering. Now their shares are worth four times what they paid for them, and the buyout market is suddenly hot. 

Who is buying BK?
3G Capital, a Brazilian-backed private equity firm led by billionaires who also own a large stake in Anheuser-Busch InBev NV, the world's largest brewer. 3G is betting it can draw on its beer-selling experience to improve Burger King's fortunes.

Wait, Burger King will be owned by Brazilians?
Yes. But that's not such a surprise, say Peter Lattman and Andrew Ross Sorkin in The New York Times. "Brazilian companies, armed with relatively strong balance sheets and backed by a vibrant domestic economy, have been growing by snapping up or merging with companies abroad" this year. 

What will the Brazilian buyout mean for customers?
You might want to keep an eye out for the Whopper com Gostinho de Churrasco, a bacon-heavy burger already sold in Brazilian Burger Kings. And the value-menu prices might rise under new ownership, as the current deals are "a bit too irresistible" for profitability. But most of the near-term menu changes, including fancier breakfast items and Seattle's Best Coffee, are already slated to roll out this fall.

Sources: Reuters, New York Times, Economist, Bloomberg, Christian Science Monitor, Breaking Views, The Street